Degradation of polyesters employing organometallic complexes of amine TRIS(phenolate) ligands

Abstract

A process for the decomposition of a polyester (e.g., an aliphatic polyester such as polyflactic acid)) to the cyclic ester monomer from which it is produced, (e.g., a lactide), which employs an organometallic complex of an amine tris(phenolate) ligand is provided. Also provided is a cyclic ester formed by the process, a (e.g., recycled) polyester formed of such a cyclic ester, processes of preparing self-decomposing / recyclable polyesters, and processes of recycling polyesters.

Description

[0001] DEGRADATION OF POLYESTERS EMPLOYING ORGANOMETALLIC COMPLEXES OF AMINE TRIS(PHENOLATE) LIGANDS

[0002] RELATED APPLICATION

[0003] This application claims the benefit of priority under 35 USC § 119(e) of U.S. Provisional Patent Application No. 63 / 658,918 filed on June 12, 2024, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to materials chemistry and, more particularly, but not exclusively, to a novel process for catalytic decomposition of polyesters to cyclic esters.

[0006] Poly(lactic acid) (PLA) is an aliphatic polyester derived from lactic acid. It is the most common bioplastic, is produced from com or related crops, and may be composted to harmless end-products, by decomposing to give H2O, CO2, and biomass. The good mechanical properties, biodegradability, and non-toxic degradation products of PLA make it very useful for several applications like packaging, disposable plastic products, drug delivery, sutures, textiles, and more.

[0007] The “non-environmental” solution to the end-of-life of PLA is burial in landfills - under these conditions, the plastic is decomposing slowly, probably not faster than common plastics derived from petroleum such as polyethylene and polystyrene.

[0008] The current recommended solution to PLA end-of-life is its degradation to simple materials in industrial composters. Some of these materials is carbon dioxide - a greenhouse gas harmful to the environment, and the rest include a solid waste that may be employed as a fertilizer. However, the composting time of PLA is longer than that of municipal waste, and therefore this solution is hardly practiced.

[0009] Background Art FIG. 1, left cycle, presents the current PLA life-cycle, which requires continued growing of designated crops.

[0010] PLA can be composted under industrial conditions, requiring temperatures around that of the glass transition (Tg) of the polymer (around 60 °C) and high relative humidity. The degradation of PLA occurs by a two-step process. In the initial step, high molecular weight polyester chains hydrolyze to lower molecular weight oligomers. When the molecular weight is low enough, microorganisms in the environment continue the degradation process to produce CO2 and H2O (biodegradation). However, PLA is mostly resistant to attack by microorganisms in soil or sewage under ambient conditions. Further, this process requires the continued production of new PLA, which requires agricultural land and cultivation time, and consequently competes with other agricultural processes.

[0011] A better “end-of-life” solution for PLA is therefore required and is highly sought after. The most efficient solution should involve a recycling step that will turn the PLA economy to circular, and will eliminate the dependence on annual crops substantially. Such a solution should ideally involve decomposition of PLA to a lactide monomer, which can then be used for producing PLA, and so forth.

[0012] Mechanical recycling which includes washing, shredding, melting, and re-use, possibly with addition of virgin-plastic is not applicable to PLA, because it readily degrades on thermal treatment. Therefore, chemical recycling, in which the polymer is converted to useful materials that can be employed industrially represents the most economic and most environmental-friendly method for post-consumption PLA.

[0013] Most efforts thus far have been invested in the decomposition of PLA to lactic acid or to alkyl lactate (including, for example ethyl lactate and / or methyl lactate), which are remote from the real monomer, and would therefore require substantial investment of materials and energy to convert them to the lactide monomer and then back to PLA.

[0014] Chemical recycling to monomer (CRM) of PLA, directly to lactide, as shown in FIG. 1, right cycle, has been described recently. In this process, PLA is warmed to beyond its melting temperature in the presence of a catalyst which leads to its decomposition to lactide under vacuum or gas flow, and the formed lactide is collected as a solid in a cold spot. A potential advantage of this ‘cradle-to-cradle’ process is the ability to produce polymerization-grade lactide directly from PLA items that contain additives or impurities such as stabilizers, dyes, or other polymers. However, the CRM catalysts described so far suffer from several disadvantages, which include low activity, partial epimerization to form meso-lactide impurity alongside the L-lactide rendering the monomer unsuitable for PLA production, and the need to add co-catalysts to increase activity.

[0015] Reference is made in this regard, for example, to Alberti et al., ChemistrySelect 2020, 5, 14759-14763, which describes the depolymerization of end-of-life poly (lactide) (PLA) by applying Zinc(II) acetate as a catalyst under solvent-free conditions.

[0016] Cederholm et al., Angew. Chem. Int. Ed. 2022, 61, e202204531, describes chemical recycling of poly(L-lactic acid) to the cyclic monomer L-lactide by selecting solvents that interact strongly with the monomer (dimethyl formamide or the green solvent y-valerolactone).

[0017] Gallin et al., Angew. Chem. Int. Ed. 2023, 62, e202303762, describes depolymerization of polyesters and polycarbonates using a combination of zinc dichloride and polyethylene glycol as a catalyst under reactive distillation conditions carried out at temperatures significantly below the ceiling temperature of the polymers evaluated.

[0018] McGuire et al., J. Am. Chem. Soc. 2023, 145, 36, 19840-19848, describes employing a commercial Sn(II) catalyst combined with a non-volatile poly(alcohol) for CRM of PLLA, while using neat polymer films at relatively low temperature (160 °C) under nitrogen flow or vacuum.

[0019] WO 2023 / 053128 describes a new family of Group (IV) (e.g., zirconium and hafnium) complexes bound to amine tris(phenolate)-type ligands, which exhibit unprecedented activities in the ring opening polymerization of various lactides under various conditions, including solution polymerizations at different temperatures and melt polymerizations. These complexes provide precise control on the tacticity of the obtained polymers and can therefore be utilized to provide varying block copolymers, including varying stereoblock copolymers. These catalysts feature several desired properties: (1) they exhibit very high activities and turn-over numbers in polymerization of L-lactide to Poly(L-lactic acid) in the melt, and (2) their preference to polymerize meso-lactide over L-lactide resulted in formation of stereo-gradient-PLA when mixtures of L-lactide contaminated with meso-lactide are employed as starting material in meltpolymerizations, whose properties exceeded those of stereo-random-PLA produced with the industrial catalyst tin octanoate.

[0020] WO 2023 / 053127 describes the use of these complexes in preparing highly stereocontrolled poly (lactic acid).

[0021] Additional Background Art includes WO 2017 / 137990; Hador et al., ACS Catal. 2022, 12, 4872-4879; Hador et al., Angew. Chem. Int. Ed. 2022, e202207652; Tu et al., Nat. Commun. 2023, 14, 3198; Davidson et al, Chem. Commun. 2003, 3, 1832-1833; Chmura et al., Chem. Commun. 2008, 1293-1295; and Koi et al., Inorg. Chem. Commun. 2001, 4, 177-179.

[0022] SUMMARY OF THE INVENTION

[0023] According to an aspect of some embodiments of the present invention there is provided a process of obtaining a cyclic ester that forms a polyester by ring opening polymerization thereof (chemical recycling to monomer; CRM), from a composition that comprises the polyester, the process comprising contacting the composition with a catalyst system that forms an organometallic complex represented by Formula A:

[0024] [(L)m(M)(X)z(X’)q]n

[0025] Formula A wherein:

[0026] M is a transition metal; n is an integer, representing the nuclearity of the complex, and can be, for example, 1, 2, 3, 4 or higher (e.g., from 1 to 8); m is a positive integer, for example, 1 or 2; z and q are each independently 0 or 1, wherein, preferably, z equals to or is higher than q;

[0027] X is a monoanionic ligand which, when present, forms a covalent or coordinative bond with the metal;

[0028] X’ is a neutral ligand, such as an alcohol which, when present, forms a coordinative bond with the metal; and

[0029] L is a ligand derived from a ligand precursor represented by Formula IV :

[0030] Formula IV wherein:

[0031] W, Y and Z are each independently an arylene or a heteroarylene, at least one of W, Y and Z being a substituted arylene or a substituted heteroarylene, the at least one substituted arylene or heteroarylene comprising at least one aliphatic, alicyclic or aromatic substituent; and

[0032] B l, B2 and B3 are each independently a bridging moiety linking between the respective aryl or heteroaryl and the nitrogen atom, or is absent, and wherein: at least one, and preferably each, of the -OH groups in the ligand precursor forms an M- O- bond with the metal, wherein the dashed line independently represents a covalent or coordinative bond; and the N is optionally attached to the M via a covalent or coordinative bond, and can be protonated or non-protonated, the process further comprising subjecting a reaction mixture comprising the composition and the organometallic complex to a condition that effects degradation of the polyester, to thereby obtain the cyclic ester. According to some embodiments of any of the embodiments described herein, M is a Group IV metal or is a tetravalent metal.

[0033] According to some embodiments of any of the embodiments described herein, M is zirconium.

[0034] According to some embodiments of any of the embodiments described herein, X is selected from alkyl, alkaryl, cycloalkyl, aryl, amide, alkoxy, thioalkoxy, aryloxy, thioaryloxy, halo and amine.

[0035] According to some embodiments of any of the embodiments described herein, X’ is a neutral ligand selected from alkyl alcohol, aryl alcohol, aralkyl alcohol, and amine.

[0036] According to some embodiments of any of the embodiments described herein, z and q are each 1, and X and X’ form together a monoanionic bidentate ligand.

[0037] According to some embodiments of any of the embodiments described herein, each of the bridging moieties B 1, B2 and B3 is independently a hydrocarbon of 1 to 6, or from 1 to 4, or from 1 to 2, carbon atoms in length.

[0038] According to some embodiments of any of the embodiments described herein, B l is represented by the Formula:

[0039] -(CRaRb)-(CRcRd)ml- wherein: ml is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0040] Ra, Rb, Rc and Rd are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ra and Rb and / or Rc and Rd, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rc and Rd in each (CRcRd) unit can be the same or different, and one or both Rc and Rd in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rc and Rd of an adjacent unit.

[0041] According to some embodiments of any of the embodiments described herein, B2 is represented by the Formula:

[0042] -(CReRf)-(CRgRh)m2- wherein: m2 is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0043] Re, Rf, Rg and Rh are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Re and Rf and / or Rg and Rh, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rg and Rh in each (CRgRh) unit can be the same or different, and one or both Rg and Rh in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rg and Rh of an adjacent unit.

[0044] According to some embodiments of any of the embodiments described herein, B3 is represented by the Formula:

[0045] -(CRiRj)-(CRkRm)m3- wherein: m3 is 0 or is a positive an integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0046] Ri, Rj, Rk and Rm are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ri and Rj and / or Rk and Rm, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rk and Rm in each (CRkRm) unit can be the same or different, and one or both Rk and Rm in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rk and Rm of an adjacent unit.

[0047] According to some embodiments of any of the embodiments described herein, each of Y, Z and W is independently an arylene.

[0048] According to some embodiments of any of the embodiments described herein, the ligand precursor (proligand) is represented by Formula V :

[0049] wherein: Bi, B2 and B 3 are as defined in any one of claims 1-10; and

[0050] R1-R12 are each independently selected from hydrogen, alkyl, cycloalkyl, heteroalicyclic, aryl, heteroaryl, halo, alkoxy, and amino, or alternatively, two of R1-R4, and / or two of Rs-Rs, and / or two of R9-R12 independently form together a cyclic ring (fused to the phenolate ring), wherein at least one of R1-R12 is alkyl, cycloalkyl, aryl or heteroaryl, each independently being substituted or unsubstituted.

[0051] According to some embodiments of any of the embodiments described herein, the ligand precursor (proligand) is represented by Formula VI: Formula VI wherein

[0052] Ra, Rb, Re, Rf, Ri and Rj are each as defined in any one of claims 6 to 8.

[0053] According to some embodiments of any of the embodiments described herein, at least one, or each, of Ri, Rs and R9 is a substituted or unsubstituted aryl or heteroaryl.

[0054] According to some embodiments of any of the embodiments described herein, at least one, or each, of Ri, Rs and R9 is a substituted or unsubstituted alkyl, preferably a lower, non-bulky, alkyl (e.g., methyl, ethyl, and / or propyl).

[0055] According to some embodiments of any of the embodiments described herein, at least one of R2-R4, Re-Rs and R10-R12 is an alkyl, preferably a lower alkyl.

[0056] According to some embodiments of any of the embodiments described herein, the lower alkyl is a non-bulky lower alkyl (e.g., methyl, ethyl, and / or propyl).

[0057] According to some embodiments of any of the embodiments described herein, m is 1.

[0058] According to some embodiments of any of the embodiments described herein, M is a tetravalent group 4 metal (preferably zirconium), and wherein preferably, z and q are each 1.

[0059] According to some embodiments of any of the embodiments described herein, the complex is represented by Formula II or Formula III:

[0060] Formula II

[0061]

[0062] Formula III wherein: n is the integer representing the nuclearity of the complex, as defined herein; and the dashed line represents a covalent or a coordinative bond representing a bond between a donor atom and the metal.

[0063] According to some embodiments of any of the embodiments described herein, m is 2. According to some embodiments of any of the embodiments described herein, M is a tetravalent group 4 metal (preferably zirconium), and wherein preferably, z and q are each 0.

[0064] According to some embodiments of any of the embodiments described herein, the complex is represented by Formula X or Formula XI:

[0065] Formula X

[0066]

[0067] Formula XI wherein: the dashed line represents a covalent or a coordinative bond representing a bond between a donor atom and a metal; and

[0068] Bi, B2, B3 R1-R12, Ra, Rb, Re, Rf, Ri and Rj are each as defined herein, and can be the same or different in each ligand.

[0069] According to some embodiments of any of the embodiments described herein, the catalyst system or the composition further comprises a hydroxy-containing material.

[0070] According to some embodiments of any of the embodiments described herein, contacting the polyester and the catalyst system is performed in the presence of a hydroxy-containing compound.

[0071] According to some embodiments of any of the embodiments described herein, the hydroxycontaining material is non-volatile (e.g. features a boiling temperature higher than 300 °C).

[0072] According to some embodiments of any of the embodiments described herein, the hydroxycontaining material is Rk(OH)p, wherein p is an integer of from 1 to 6, and Rk is alkyl, cycloalkyl, alkaryl or aryl, or is a polymeric moiety.

[0073] According to some embodiments of any of the embodiments described herein, the polymeric moiety is or comprises a poly (alkylene glycol).

[0074] According to some embodiments of any of the embodiments described herein, a molecular weight Mn of the poly(alkylene glycol) is lower than 2,000, or lower than 1,000, or lower than 600 grams / mol.

[0075] According to some embodiments of any of the embodiments described herein, a mol ratio of the hydroxy-containing material to the metal complex is in a range of from 1: 1 to 100: 1 or from 1: 1 to 50: 1, or from 10: 1 to 50: 1, or from 10: 1 to 30: 1. According to some embodiments of any of the embodiments described herein, at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 % of the obtained cyclic ester features substantially the same stereoconfiguration as the backbone units of the polyester (formed by ROP of the cyclic ester).

[0076] According to some embodiments of any of the embodiments described herein, the cyclic ester is or comprises a lactide, and the polyester is or comprises a poly(lactic acid) (PLA).

[0077] According to some embodiments of any of the embodiments described herein, the lactide is selected from homochiral lactide, racemic lactide and meso-lactide and any combination thereof, and wherein at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 % of the lactide features the same stereoconfiguration as the backbone units of the polyester.

[0078] According to some embodiments of any of the embodiments described herein, the organometallic complex is formed in situ such that the contacting is with a catalyst system that comprises the ligand precursor, and a catalyst precursor (metal reagent) M(X)z(Xi)w(X’)q, wherein:

[0079] M is the transition metal, w is 0 or is an integer which together with z provides the valence number of the metal; z and q are as defined herein;

[0080] X and X’ are each as defined herein; and

[0081] Xi is a monoanionic ligand, which can be the same or different from X, wherein when w is higher than 1, each Xi can be the same or different.

[0082] According to some embodiments of any of the embodiments described herein, the condition for effecting the degradation comprises heating the mixture.

[0083] According to some embodiments of any of the embodiments described herein, the heating is at a temperature at which the polyester is in a molten state.

[0084] According to some embodiments of any of the embodiments described herein, the process further comprises separating the cyclic ester from the composition.

[0085] According to some embodiments of any of the embodiments described herein, the separating is by sublimating the cyclic ester and collecting it as a solid product.

[0086] According to some embodiments of any of the embodiments described herein, the separating is by distillation.

[0087] According to some embodiments of any of the embodiments described herein, the composition comprises polymeric materials other than the polyester, and wherein at least 90 %, or at least 95 %, or at least 98 %, of a product obtained by the process consists of the cyclic ester. According to some embodiments of any of the embodiments described herein, the composition is exposed to aerobic environment prior to subjecting to the condition.

[0088] According to some embodiments of any of the embodiments described herein, the composition that comprises the polyester further comprises the organometallic complex, and the process comprises subjecting the composition to the condition that effects degradation of the polyester.

[0089] According to some embodiments of any of the embodiments described herein, subjecting to the condition is performed during a time period that ranges from 1 day to 720, or from 1 to 365, or from 1 to 200, days, after the polyester that further comprises the organometallic complex is prepared.

[0090] According to some embodiments of any of the embodiments described herein, the process further comprises subjecting the cyclic ester to ring opening polymerization to thereby obtain the polyester (e.g., as a recycled polyester).

[0091] According to an aspect of some embodiments of the present invention there is provided a cyclic ester obtained by the process as described herein in any of the respective embodiments and any combination thereof.

[0092] According to some embodiments of any of the embodiments described herein, the cyclic ester is usable in preparing a (e.g., recycled) polyester, for example, by ring-opening polymerization (ROP).

[0093] According to an aspect of some embodiments of the present invention there are provided a recycled polyester, a composition comprising a recycled polyester and an article-of-manufacturing comprising a recycled polyester, wherein the recycled polyester is prepared (e.g., by ROP) from a cyclic ester obtained by a process as described herein in any of the respective embodiments and any combination thereof.

[0094] According to an aspect of some embodiments of the present invention there is provided a process of preparing a polyester that is capable of decomposing into the cyclic ester from which the polyester is formed (a recyclable polyester or a self-decomposing or self-degrading polyester), the process comprising contacting the cyclic ester with a catalyst system that comprises an organometallic complex as defined herein in any of the respective embodiments and any combination thereof, to thereby obtain a polyester-containing material, optionally, maintaining the polyester or a composition or an article-of-manufacturing comprising same under conditions that maintain an activity of the organometallic complex, wherein the decomposing comprises subjecting the polyester or a composition or article- of-manufacturing comprising same to a condition that effects degradation of the polyester. According to some embodiments of any of the embodiments described herein, the decomposing further comprises contacting the polyester or a composition or article-of- manufacturing comprising same with a metal reagent (e.g., as described herein in any of the respective embodiments and any combination thereof) and / or a hydroxy-containing material (e.g., as described herein in any of the respective embodiments and any combination thereof) that reactivates the organometallic complex.

[0095] According to an aspect of some embodiments of the present invention there is provided a self-decomposing (or self-degrading; or recyclable) polyester that is capable of decomposing into the cyclic ester from which the polyester is formed (e.g., via CRM).

[0096] According to an aspect of some embodiments of the present invention there is provided a self-decomposing (or self-degrading; or recyclable) polyester (capable of undergoing self-CRM) that is capable of decomposing / degrading into the cyclic ester from which the polyester is formed, prepared by the process as described herein in any of the respective embodiments and any combination thereof.

[0097] According to an aspect of some embodiments of the present invention there is provided an article-of-manufacturing comprising a self-decomposing (or self-degrading; or recyclable) polyester as described herein in any of the respective embodiments and any combination thereof.

[0098] According to an aspect of some embodiments of the present invention there is provided a process of recycling a polyester, the process comprising contacting a polyester or a composition or article-of-manufacturing comprising same with a catalyst system that forms an organometallic complex as defined herein in any of the respective embodiments and any combination thereof, under a condition that effects degradation of the polyester to the cyclic ester that composes it, to thereby obtain the cyclic ester; subjecting the cyclic ester to a condition that effects ring opening polymerization, thereby obtaining a recycled polyester; optionally integrating the recycled polyester in a composition or an article-of- manufacturing; and optionally repeating the contacting with the catalysts system to thereby obtain the cyclic ester, and thereafter subjecting the recycled polyester or the composition or article-of- manufacturing comprising same to a condition that effects degradation of the polyester.

[0099] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0100] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0101] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0102] In the drawings:

[0103] FIG. 1 (Background Art) presents the current PLA life-cycle, which requires continued growing of designated crops (left, bigger cycle), and the suggested direct chemical recycling of PLA to its monomer and back (right, smaller cycle).

[0104] FIG. 2A presents the chemical structures of exemplary amine tris(phenolate) ligands used to generate respective exemplary zirconium complexes employed in depolymerization of PLLA, and of exemplary currently practiced catalysts.

[0105] FIG. 2B presents the crystallographic structure of Lig1Zr(O-zPr)(HO-zPr), an exemplary metal complex according to some emobodiments of the present invention. All non-hydrogen atoms are presented as 50 % thermal ellipsoids. H atoms and solvent molecule (hexane) omitted for clarity. The isopropoxide group is trans to the amine donor and the isopropanol group is trans to 031. The isopropoxide, isopropanol, and two tert-butyl groups are disordered with 50:50 occupancy, and for clarity, only one orientation of the two parts of these groups is shown. Selected bond lengths (A): Zrl-O22.013(1), Zrl-O31 2.006(1), Zrl-052 2.016(1), Zrl-0662.343(2), Zrl- 070 1.933(2), Zrl-N23 2.470(1).

[0106] FIG. 2C presents the crystallographic structure of Lig1Zr(O-zPr)(HO-zPr) shown in FIG. 2B, including the disordered groups (isopropoxide, isopropanol, and two tert-butyl groups) and the solvent molecule (hexane).

[0107] FIG. 3 presents photographs of sublimators used in depolymerization of PLA-consisting cap (right), and a mixture of PLA-consisting cap and a PET-bottle, according to some embodiments of the present invention. DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0108] The present invention, in some embodiments thereof, relates to materials chemistry and, more particularly, but not exclusively, to novel processes for catalytic decomposition / degradation of polyesters to cyclic esters, for preparing recyclable and / or self-decomposing / self-degrading polyesters and for recycling polyesters.

[0109] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0110] As discussed hereinabove, the current end-of-life solutions of PLA and other polyesters are not environmentally-benign, and, moreover, require the continued growth of “crops-for- plastics”. Simple burial of PLA and other polyester materials in landfills does not lead to its degradation; decomposition of PLA in industrial composters is a slow-process which produces carbon dioxide; mechanical recycling is not applicable to PLA; and hydrolysis of PLA back to lactic acid is not effective energy-wise and material-wise.

[0111] The limited variety of catalysts for the process of degradation of polyesters directly to monomers have prompted the present inventors to attempt employing complexes of amine tris(phenolate) in the depolymerization of polyesters such as PLA to the cyclic ester (e.g., lactide) monomer that forms the polyester, while aiming to achieve, for example, a genuine circular economy of PLA that would minimize the demand for continued growing of crops for production of the monomer.

[0112] This backward reaction is broadly termed: Chemical Recycling to Monomer (CRM). In a typical CRM process, PLA is warmed beyond its melting temperature in the presence of a catalyst which leads to its decomposition to lactide. The formed lactide can be carried away by, for example, vacuum or gas flow, and can be collected as a solid, for example, in a cold spot. This lactide can then be used directly for the production of new PLA.

[0113] The methodology described herein, of Chemical Recycling to Monomer (CRM), decomposes the polyester to pure cyclic ester monomer in a single step, and the obtained cyclic ester monomer, such as lactide, can be employed for production of, for example, PLA with identical properties to those of the virgin-PLA.

[0114] The amine tris(phenolate) metal complexes used in this methodology were demonstrated to be more effective than the currently known catalysts for this transformation, produce highly pure lactide, as an exemplary cyclic ester, without side reactions (such as epimerization), and, by being selective to polyesters such as PLA, do not require the sorting of PLA from other plastics. Exposing the catalytic system to aerobic environment resulted in even better performance. Moreover, it has been demonstrated that polyesters prepared using amine tris(phenolate) metal complexes as described herein, for example, as described in WO 2023 / 053128, can undergo CRM to provide a highly pure cyclic ester, simply by subjecting these polyesters to conditions that promote decomposition, due to the presence of a residual amount of the metal complex in the polyester. Such polyesters may optionally undergo decomposition via CRM also upon addition of a metal reagent such as MX1X2X3X’, wherein X’ is as defined herein and each of Xi, X2 and X3 is independently a mono-anionic ligand as described herein, while exploiting residual amounts of the amine tris(phenolate) ligand in the polyester and in situ generation of the active metal complex.

[0115] These findings allow preparing polyesters such as PLA, or PLLA, which can selfdecompose via CRM when subjected to suitable conditions, and which can be finely tuned to undergo such a decomposition, for example, by controlling the amount of the metal complex used for preparing the polyesters, to thereby control the amount of residual active metal complex that can later effect the CRM decomposition of the polyester.

[0116] The herein disclosed methodology may turn the PLA economy to circular, carrying a substantial environmental benefit, reducing the extent of the annual growth of designated crops for plastics, reducing the energy consumption of the PLA production process, and contributing to making of this environmentally-benign PLA polymer more prevalent, thereby reducing pollution of soil and water. The produced lactide monomer can be directly employed for production of new PLA (e.g., as a recycled PLA) without compromising the properties of the plastic, using the same catalysts (metal complexes) or any other suitable catalyst to form PLA again (i.e., it is ‘ ‘polymerization-grade’ ’ lactide) .

[0117] Some embodiments of the present invention relate to a method of depolymerization or degradation of a polyester to the cyclic ester that forms the polyester, that is, to the cyclic ester that corresponds to the backbone units of the polyester, or, in other words, to a method performing CRM of a polyester. Some embodiments of the present invention relate to a method of depolymerization or degradation of the plastic poly(lactic acid) (PLA), for example, of poly(L- lactic acid) (PLLA), directly to the monomer from which it is produced - lactide, for example, L- lactide - by metal complexes of amine tris(phenolate) ligands, at elevated temperatures.

[0118] According to an aspect of some embodiments of the present invention, there is provided a process of obtaining a cyclic ester that forms a polyester by ring opening polymerization thereof, from a composition that comprises the polyester. According to some embodiments, the process as described herein is regarded as a process of degrading or decomposing the polyester into the cyclic ester repeating units that form the polyester.

[0119] According to some embodiments, the process as described herein is regarded as a process of CRM of a polyester.

[0120] According to the present embodiments, the process comprises contacting the polyester or a composition that comprises the polyester with a catalyst system that forms an organometallic complex represented by Formula A:

[0121] [(L)m(M)(X)z(X’)q]n

[0122] Formula A wherein:

[0123] M is a transition metal; n is a positive integer, representing the nuclearity of the complex, and can be, for example, 1, 2, 3, 4 or higher (e.g., from 1 to 10 or from 1 to 8, or from 1 to 6, or from 1 to 4, including any intermediate values and subranges therebetween); m is a positive integer (e.g., from 1 to 10 or from 1 to 8, or from 1 to 6, or from 1 to 4, including any intermediate values and subranges therebetween), and is preferably 1 or 2; z and q are each independently 0 or 1, wherein, preferably, z equals to or is higher than q (e.g., either z and q are each 1, z and q are each 0, or z is 1 and q is 0);

[0124] X is a monoanionic ligand which, when present, forms a covalent or coordinative bond with the metal;

[0125] X’ is a neutral ligand, such as an alcohol which, when present, forms a coordinative bond with the metal; and

[0126] L is a ligand derived from a ligand precursor represented by Formula IV :

[0127] Formula IV wherein:

[0128] W, Y and Z are each independently arylene or heteroarylene, at least one of W, Y and Z being a substituted arylene or heteroarylene, the at least one substituted arylene or heteroarylene comprising at least one aliphatic (e.g., alkyl), alicyclic or aromatic (aryl or heteroaryl) substituent; and

[0129] B l, B2 and B3 are each independently a bridging moiety linking between the respective aryl or heteroaryl and the nitrogen atom, or is absent, and wherein: at least one, and preferably each, of the -OH groups in the ligand precursor form an M— O- bond with the metal, wherein the dashed line independently represents a covalent or coordinative bond; and the N (nitrogen atom) is optionally attached to the M via a covalent or coordinative bond, and can be protonated or non-protonated.

[0130] When n is 1, the complex is a mononuclear complex. When n is 2 or higher, the complex is a polynuclear complex. When n is 2, the complex is a binuclear complex. It is to be noted that polynuclear complexes may include other species or moieties in coordination with one or more of the metal atoms.

[0131] The ligand precursor is also referred to herein interchangeably simply as a ligand or as a proligand.

[0132] A ligand derived from a ligand precursor means the actual chemical moiety that is bound to a metal atom upon forming the organometallic complex. Typically, one, two or all of the hydroxy groups of the ligand precursor are converted to an -O — group, which is coordinated with the metal, in the ligand.

[0133] Exemplary ligand precursors according to some embodiments of the present invention are presented in FIG. 2A.

[0134] Herein throughout, the phrase “organometallic complex” is also referred to interchangeably as a “metal complex” or simply as a “complex”.

[0135] According to some embodiments of any of the embodiments described herein, the process further comprises subjecting a reaction mixture that comprises the composition (which comprises the polyester) and the organometallic complex to a condition that effects degradation of the polyester to thereby obtain the cyclic ester.

[0136] According to some embodiments of any of the embodiments described herein, the organometallic complex acts as a pre-catalyst, which is activated during the process (e.g., during the contacting and / or during subjecting the reaction mixture to a condition as described herein). For example, the organometallic complex can be activated in the presence of a co-catalyst, a hydroxy-containing compound and / or other species or substances that become in contact with the complex (e.g., air, environmental humidity, traces of humidity in the composition and / or the polyester itself), during the contacting and / or the subjecting steps as described herein. Alternatively, or in addition, the organometallic complex can be activated when the mixture is subjected to a condition as described herein (e.g., heating), optionally in the presence of air, environmental humidity, traces of humidity in the composition and / or the polyester itself. According to some embodiments of any of the embodiments described herein, M is a Group IV metal, such as zirconium or hafnium, preferably zirconium. According to some embodiments of any of the embodiments described herein, M is a tetravalent metal, or has at least 4 coordinative sites.

[0137] According to some embodiments of the present invention, the organometallic complex can be represented by Formula I:

[0138] Formula I wherein: n is 1, 2, 3 or 4, representing the nuclearity of the complex (e.g., when n is 1 the complex is a mononuclear complex and when n is 2 the complex is a dinuclear complex); the dashed line represents a covalent or a coordinative bond, representing a bond between a donor atom and a metal;

[0139] M is the tetravalent (group 4) metal (e.g., zirconium or hafnium, preferably zirconium);

[0140] X is a monoanionic ligand, as described herein in any of the respective embodiments;

[0141] X’ is a neutral ligand, as described herein in any of the respective embodiments, such as an alcohol, or is absent;

[0142] W, Y and Z are each independently an aryl or a heteroaryl, at least one of W, Y and Z being a substituted aryl or heteroaryl, the substituted aryl or heteroaryl comprising at least one aromatic (aryl or heteroaryl) substituent, as described herein in any of the respective embodiments; and B l, B2 and B3 are each independently a bridging moiety linking between the respective aryl or heteroaryl and the nitrogen atom, as described herein in any of the respective embodiments, or is absent.

[0143] By “tetravalent metal” it is meant a metal that has a valency of 4, that is, is capable of forming at least four covalent bonds with four monovalent atoms. A “tetravalent metal” encompasses also metals which feature higher valency. In some of any of the embodiments described herein, M is zirconium or hafnium. Other tetravalent metals are also contemplated.

[0144] In some preferred embodiments, M is a Group IV metal.

[0145] In some preferred embodiments, M is zirconium.

[0146] In some preferred embodiments, M is hafnium.

[0147] Herein and in the art, a “monoanionic ligand” describes a ligand (which can be an atom or a chemical group) that is negatively charged, and has a net charge (before being complexed to the metal) of -1, as a monoanion.

[0148] The monoanionic ligand X can be, as non-limiting examples, alkyl (substituted or unsubstituted), cycloalkyl (substituted or unsubstituted), aryl (substituted or unsubstituted), amide, alkoxy, thioalkoxy, aryloxy, thioaryloxy, halo or amine (substituted or unsubstituted), as these terms are defined herein.

[0149] It is noted that when an amine is bound to a metal atom, the resulting moiety is also referred to herein and in the art as “amide”, that is, a M-NR’R” moiety as described herein is also referred to herein and in the art as a metal amide.

[0150] Herein and in the art, a “neutral ligand” describes a ligand (a chemical group) that has a zero net charge (before being complexed to the metal).

[0151] The neutral ligand X’, if present, can be, as non-limiting examples, alkyl alcohol, aryl alcohol, amine, etc., or be absent. Alternatively X and X’ could form together a monoanionic bidentate ligand, such as acetyl-acetonato, methyl-lactate, 1,2-ethanediol monomethyl ether, or N, A ’-di methyl- 1 ,2-ethanolamine.

[0152] In some of any of the embodiments described herein for Formula I, M is zirconium, and X is alkoxy or aryloxy. In some of these embodiments, X is alkoxy, and the alkyl portion of the alkoxy is preferably a lower alkyl, of 2 to 6, or of 3 to 6, carbon atoms, and is further preferably a branched lower alkyl, for example, tert-butyl or iso-propyl. Other branched alkyls, preferably lower alkyls, are contemplated.

[0153] In some of any of the embodiments described herein for Formula I, M is zirconium and X is O-isopropyl (also referred to herein as isopropoxy). In some of any of the embodiments described herein for Formula I, M is zirconium and X is O-tert-butyl (also referred to herein as tert-butoxy).

[0154] In some of any of the embodiments described herein for Formula I, M is hafnium and X is alkoxy or aryloxy. In some of these embodiments, X is alkoxy, and the alkyl portion of the alkoxy is preferably a lower alkyl, of 2 to 6, or of 3 to 6, carbon atoms, and is further preferably a branched lower alkyl, for example, tert-butyl or iso-propyl. Other branched alkyls, preferably lower alkyls, are contemplated.

[0155] In some of any of the embodiments described herein, X’ is an alcohol, preferably a monoalcoholic aliphatic moiety such as a hydroxyalkyl. The alkyl portion of the alcohol is preferably a lower alkyl, of 2 to 6, or of 3 to 6, carbon atoms, and is further preferably a branched lower alkyl, for example, tert-butyl or iso-propyl. Other branched hydroxy alkyls, preferably lower hydroxyalkyls, are contemplated.

[0156] In exemplary embodiments, M is zirconium or hafnium, X is an alkoxy as described herein, and X’ is a hydroxyalkyl, as described herein.

[0157] In exemplary embodiments, M is zirconium, X is an alkoxy as described herein, and X’ is a hydroxyalkyl, as described herein.

[0158] In exemplary embodiments, M is zirconium or hafnium, X is an alkoxy in which the alkyl portion is preferably a lower alkyl, of 2 to 6, or of 3 to 6, carbon atoms, and is further preferably a branched lower alkyl, for example, tert-butyl or iso-propyl, and X’ is a hydroxyalkyl in which the alkyl portion is preferably a lower alkyl, of 2 to 6, or of 3 to 6, carbon atoms, and is further preferably a branched lower alkyl, for example, tert-butyl or iso-propyl.

[0159] According to some embodiments, the bond between one or more, or all, of the three oxygen atoms (which are derived from the hydroxy groups in the ligand precursor as described herein) and the metal atom M is a covalent bond.

[0160] According to some embodiments, the bond between the monoanionic ligand X and the metal atom M is a covalent bond.

[0161] According to some embodiments, the bond between one, two, or each of the three oxygen atoms (which are derived from the hydroxy groups in the ligand precursor as described herein) and the metal atom M is a covalent bond, and the bond between the monoanionic ligand X and the metal atom M is a covalent bond.

[0162] According to some embodiments, the bond between the nitrogen (amine) moiety (which is derived from the amine in the ligand precursor as described herein) and the metal atom M is a coordinative bond. According to some embodiments, the bond between the neutral ligand X’ and the metal atom M is a coordinative bond.

[0163] According to some embodiments, each of the bond between the nitrogen (amine) moiety (which is derived from the amine in the ligand precursor as described herein) and the metal atom M and the bond between the neutral ligand X’ and the metal atom M is a coordinative bond.

[0164] According to some embodiments, the bond between one, two or each of the three oxygen atoms (which are derived from the hydroxy groups in the ligand precursor as described herein) and the metal atom M is a covalent bond, the bond between the monoanionic ligand X and the metal atom M is a covalent bond, the bond between the nitrogen (amine) moiety (which is derived from the amine group in the ligand precursor as described herein) and the metal atom M is a coordinative bond, and the bond between the neutral ligand X’ and the metal atom M is a coordinative bond.

[0165] However, any other arrangement is also contemplated.

[0166] Any one of the bridging moieties, Bl, B2 and B3, independently, can be a hydrocarbon chain, as defined herein.

[0167] Herein, the term “hydrocarbon” describes an organic moiety that includes, as its basic skeleton, a chain of carbon atoms, also referred to herein as a backbone chain, substituted mainly by hydrogen atoms. The hydrocarbon can be saturated or unsaturated, be comprised of aliphatic, alicyclic and / or aromatic moieties, and can optionally be substituted by one or more substituents (other than hydrogen). A substituted hydrocarbon may have one or more substituents, whereby each substituent group can independently be, for example, alkyl, cycloalkyl, alkenyl, alkynyl, alkaryl, aryl, heteroaryl, heteroalicyclic, amine, halo, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, azide, sulfonamide, carboxy, thiocarbamate, urea, thiourea, silyl, carbamate, amide, and hydrazine, and any other substituents as described herein.

[0168] The hydrocarbon moiety can optionally be interrupted by one or more heteroatoms, including, without limitation, one or more oxygen, nitrogen (substituted or unsubstituted, as defined herein for -NR’-) and / or sulfur atoms.

[0169] In some embodiments of any of the embodiments described herein the hydrocarbon is not interrupted by any heteroatom, nor does it comprise heteroatoms in its backbone chain, and can be an alkylene chain, or be comprised of alkyls, cycloalkyls, aryls, alkenes and / or alkynes, covalently attached to one another in any order.

[0170] In some of any of the embodiments described herein, the hydrocarbon is an alkylene chain, which can be unsubstituted or substituted, as described herein. According to some of any of the embodiments described herein, each of the bridging moieties is independently a hydrocarbon (e.g., as defined herein) of 1 to 6, or from 1 to 4, or from 1 to 2, carbon atoms in length, or is absent.

[0171] According to some embodiments, Bl is represented by the Formula:

[0172] -(CRaRb)-(CRcRd)ml- wherein: ml is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0173] Ra, Rb, Rc and Rd are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ra and Rb and / or Rc and Rd, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rc and Rd in each (CRcRd) unit can be the same or different, and one or both Rc and Rd in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rc and Rd of an adjacent unit.

[0174] In exemplary embodiments, ml is 0.

[0175] In exemplary embodiments, Ra and Rb are each hydrogen.

[0176] In exemplary embodiments, ml is 0 and Ra and Rb are each hydrogen.

[0177] In exemplary embodiments, B 1 is an alkylene of 1 to 6, or 1 to 4, or 1 to 3, or 1 or 2, carbon atoms in length. In exemplary embodiments, the alkylene is an unsubstituted alkylene. In exemplary embodiments, B l is methylene, for example, unsubstituted methylene.

[0178] According to some embodiments, B2 is represented by the Formula:

[0179] -(CReRf)-(CRgRh)m2- wherein: m2 is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0180] Re, Rf, Rg and Rh are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Re and Rf and / or Rg and Rh, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rg and Rh in each (CRgRh) unit can be the same or different, and one or both Rg and Rh in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rg and Rh of an adjacent unit.

[0181] In exemplary embodiments, m2 is 0.

[0182] In exemplary embodiments, Re and Rf are each hydrogen.

[0183] In exemplary embodiments, m2 is 0 and Re and Rf are each hydrogen.

[0184] In exemplary embodiments, B2 is an alkylene of 1 to 6, or 1 to 4, or 1 to 3, or 1 or 2, carbon atoms in length. In exemplary embodiments, the alkylene is an unsubstituted alkylene. In exemplary embodiments, B2 is methylene, for example, unsubstituted methylene.

[0185] According to some embodiments, B3 is represented by the Formula:

[0186] -(CRiRj)-(CRkRm)m3- wherein: m3 is 0 or is a positive an integer of from 1 to 5, or from 1 to 3, or from 1 to 2;

[0187] Ri, Rj, Rk and Rm are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ri and Rj and / or Rk and Rm, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rk and Rm in each (CRkRm) unit can be the same or different, and one or both Rk and Rm in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rk and Rm of an adjacent unit.

[0188] In exemplary embodiments, m3 is 0.

[0189] In exemplary embodiments, Ri and Rj are each hydrogen.

[0190] In exemplary embodiments, m3 is 0 and Ri and Rj are each hydrogen.

[0191] In exemplary embodiments, B3 is an alkylene of 1 to 6, or 1 to 4, or 1 to 3, or 1 or 2, carbon atoms in length. In exemplary embodiments, the alkylene is an unsubstituted alkylene. In exemplary embodiments, B3 is methylene, for example, unsubstituted methylene.

[0192] According to some of any of the embodiments described herein, each of Y, Z and W is independently an aromatic moiety or group, such that each can independently be an aryl or a heteroaryl, as these terms are defined herein. According to some of any of the embodiments described herein, each of Y, Z and W is independently an aryl (e.g., phenyl or naphthyl). W, Y and Z can be the same or different from one another, in any combination.

[0193] According to some of any of the embodiments described herein, W, Y and Z are each the same, for example, each is the same aryl (e.g., phenyl).

[0194] In exemplary embodiments, W, Y and Z are each independently an aryl. In exemplary embodiments, W, Y and Z are each independently a phenyl, which can independently be substituted or unsubstituted.

[0195] According to some of these embodiments, the metal complexes can be collectively represented by Formula II: wherein: the dashed lines, n, X, X’, Bi, B2 and B3 are as defined herein in any of the respective embodiments and any combination thereof; and

[0196] R1-R12 are each independently selected from hydrogen, alkyl, cycloalkyl, heteroalicyclic, aryl, heteroaryl, halo, alkoxy, and amino, or alternatively, two of R1-R4, and / or two of Rs-Rs, and / or two of R9-R12 independently form together acyclic ring (fused to the phenolate ring). According to some of these embodiments, at least one of R1-R12 is a substituted or unsubstituted aryl or heteroaryl.

[0197] According to some of these embodiments, the metal complexes can be collectively represented by Formula III (when B 1, B2 and B3 are each independently a methylene, as described herein in any of the respective embodiments):

[0198]

[0199] Formula III wherein: n, X, X’, R1-R12, Ra, Rb, Re, Rf, Ri and Rj are each as defined in any of the respective embodiments.

[0200] According to some of these embodiments, at least one of R1-R12 is a substituted or unsubstituted aryl or heteroaryl. In some embodiments, at least one, or each, of W, Y and Z is a substituted or substituted naphthyl.

[0201] According to some of these embodiments, the complexes are collectively represented by Formula Ila: wherein: the dashed lines, n, X, X’, Bi, B2 and B3 are as defined herein in any of the respective embodiments and any combination thereof; and

[0202] Ri, R4, Rs, Rs, R9, R12, R13-R16, R17-R20 and R21-R24 are each independently selected from hydrogen, alkyl, cycloalkyl, heteroalicyclic, aryl, heteroaryl, halo, alkoxy, and amino, or alternatively, two or more of Ri, R4, and R13-R16, and / or two or more of R5, Rs, and R17-R20, and / or two or more of R9, R12 and R21-R24 independently form together one or more acyclic ring (fused to the phenolate ring), provided that at least one of Ri, R4, Rs, Rs, R9, R12, R13-R16, R17-R20 and R21-R24 is a substituted or unsubstituted aryl or heteroaryl.

[0203] According to some of these embodiments, the complexes can be collectively represented by Formula Illa (when B 1, B2 and B3 are each independently a methylene, as described herein in any of the respective embodiments):

[0204] Formula Illa wherein: the dashed lines, n, X, X’, Ri, R4, Rs, Rs, R9, R12, R13-R16, R17-R20 and R21-R24, Ra, Rb, Re, Rf, Ri and Rj are each as defined in any of the respective embodiments, provided that at least one of Ri, R4, Rs, Rs, R9, R12, R13-R16, R17-R20 and R21-R24 is a substituted or unsubstituted aryl or heteroaryl.

[0205] According to some of any of the embodiments described herein, e.g., for Formulae I, Ila, lib, Illa and / or Illb, the aryl or heteroaryl substituting one or more of X, Y and W is a substituted aryl or heteroaryl, and in some of these embodiments, it is substituted by one or more of alkyl, cycloalkyl, halo, aryl, alkoxy, thioalkoxy, hydroxyl, thiol, amine, amide, or any other substituent as described herein. In some embodiments, at least one, or all of the aryl or heteroaryl substituting one or more of X, Y and W is not substituted by an aryl (e.g., is unsubstituted or is substituted by one or more substituents other than aryl). In some embodiments, at least one, or all of the aryl or heteroaryl substituting one or more of X, Y and W is substituted by one or more of an alkyl and a cycloalkyl.

[0206] According to some of the embodiments related to Formulas III and Illa, when at least one of Ri, R4, Rs, Rs, R9, R12, R13-R16, R17-R20 and R21-R24 is a substituted or unsubstituted aryl, for example, a substituted or unsubstituted phenyl and / or a substituted or unsubstituted naphthyl, the aryl (e.g., phenyl or naphthyl) is either unsubstituted or substituted by a substituent other than aryl. In some of these embodiments, the aryl (e.g., phenyl or naphthyl) is substituted by one or more alkyl(s).

[0207] According to some of any of the embodiments described herein, the aryl or heteroaryl substituting one or more of X, Y and W in Formula I, or one or more of the phenol moieties in Formula II or III, or one or more of the naphthyl moieties in Formula Ila or Illa, is at the ortho position with respect to the phenolate (-O-) group.

[0208] For example, in Formula II or III, at least one of Ri, R5 and R9 is a substituted or unsubstituted aryl or heteroaryl, as described herein in any of the respective embodiments.

[0209] In exemplary embodiments of Formula II or III, at least one of Ri, R5 and R9 is a substituted or unsubstituted phenyl or a substituted or unsubstituted naphthyl or a substituted or unsubstituted anthracenyl, as described herein in any of the respective embodiments.

[0210] In exemplary embodiments of Formula II, at least one of Ri, R5 and R9 is a substituted or unsubstituted phenyl, as described herein in any of the respective embodiments.

[0211] In exemplary embodiments of Formula II, at least one of Ri, R5 and R9 is a substituted or unsubstituted anthracenyl, as described herein in any of the respective embodiments.

[0212] In exemplary embodiments of Formula III, at least one of Ri, R5 and R9 is a substituted or unsubstituted naphthyl, as described herein in any of the respective embodiments.

[0213] For example, in Formula Ila or Illa, at least one of Ri, R5 and R9 is a substituted or unsubstituted aryl or heteroaryl, as described herein in any of the respective embodiments.

[0214] In exemplary embodiments of Formula Ila or Illa, at least one of Ri, R5 and R9 is a substituted or unsubstituted phenyl or a substituted or unsubstituted naphthyl or a substituted or unsubstituted anthracenyl, as described herein in any of the respective embodiments.

[0215] In exemplary embodiments of Formula III, at least one of Ri, R5 and R9 is a substituted or unsubstituted phenyl, as described herein in any of the respective embodiments. In exemplary embodiments of Formula III, at least one of Ri, Rs and R9 is a substituted or unsubstituted anthracenyl, as described herein in any of the respective embodiments.

[0216] In exemplary embodiments of Formula Illa, at least one of Ri, Rs and R9 is a substituted or unsubstituted naphthyl, as described herein in any of the respective embodiments.

[0217] In exemplary embodiments of Formula II or III, at least one of Ri, Rs and R9 is a substituted phenyl, and the phenyl is substituted by one or more alkyl(s), preferably one or more lower alkyls, as described herein. In exemplary embodiments of Formula II or Ila, at least one of Ri, Rs and R9 is mesitylene.

[0218] In exemplary embodiments of Formula II or III, at least one of Ri, Rs and R9 is an unsubstituted phenyl.

[0219] In exemplary embodiments of Formula II or III, at least one of Ri, Rs and R9 is a an unsubstituted anthracenyl.

[0220] For any of the respective embodiments described herein, whenever two or more of Ri, Rs and R9 is a substituted or unsubstituted aryl or heteroaryl, the aryl or heteroaryl can be the same or different.

[0221] In some of any of these embodiments, the other substituents, (e.g., R2-R4, Re-Rs and R10- R12 in Formulae II and III; Ri, R4, Rs, R12, R13-R16, R17-R20 and R21-R24 in Formulae Ila and Illa) can each independently be hydrogen or an alkyl, and in some embodiments, one or more of these substituents is an alkyl, preferably a lower alkyl of e.g., 1 to 6, or 1 to 4, carbon atoms. In exemplary embodiments, one or more of these substituents is a bulky lower alkyl, namely, a branched lower alkyl such as, for example, isopropyl, isobutyl, tert-butyl, isopropyl, trityl, cumyl and tert-hexyl. In exemplary embodiments, one or more of these substituents is a non-bulky lower alkyl, namely, a lower alkyl such as, for example, methyl, ethyl or propyl. In exemplary embodiments, the alkyl is at the ortho and / or para positions with respect to the phenolate anion, for example, one or more of Ri, R3, Rs, R7, R9 and R11 is an alkyl as described herein.

[0222] As used herein, the phrase "bulky", in the context of a group or an alkyl in particular, describes a group that occupies a large volume. A bulkiness of a group or an alkyl is determined by the number and size of the atoms composing the group, by their arrangement, and by the interactions between the atoms (e.g., bond lengths, repulsive interactions). Typically, lower, linear alkyls are less bulky than branched alkyls; bicyclic molecules are more bulky than cycloalkyls, etc.

[0223] Exemplary bulky lower alkyls include, but are not limited to, branched alkyls such as tertbutyl, isobutyl, isopropyl, isopentyl, and tert-hexyl, as well as substituted alkyls such as triphenylmethane (trityl) and cumyl. In some of any of the embodiments described herein for Formula I, II and Ila, the bridging moieties B 1, B2 and B3 can be the same or different.

[0224] In some of any of the embodiments described herein for Formula I, X, Y and W can be the same or different.

[0225] In exemplary embodiments of Formula I, X, Y and W are the same.

[0226] In exemplary embodiments of Formula I, X, Y and W are the same, and Bl, B2 and B3 are the same.

[0227] In exemplary embodiments of Formula II or Ila, B 1, B2 and B3 are the same.

[0228] In exemplary embodiments of Formula II, R1, R5 and R9 are the same and are preferably a substituted or unsubstituted aryl (e.g., phenyl, naphthyl or anthracenyl); R2, R6 and R10 are the same, R3, R7 and R11 are the same; and / or R4, R8 and R12 are the same. In some of these embodiments, Bl, B2 and B3 are the same.

[0229] In exemplary embodiments of Formula III, Ri, Rs and R9 are the same and are preferably a substituted or unsubstituted aryl (e.g., phenyl); R4, Rs and R12 are the same; and / or each of the other substituents on the naphthyl rings are the same for each naphthyl. In some of these embodiments, Bl, B2 and B3 are the same.

[0230] In exemplary embodiments, the complex is represented by Formula II or Ila, and Ri, Rs and R9 are the same and each is an unsubstituted phenyl. In some of these embodiments, at least one of R2-R4, R6-Rs and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl as defined herein, such as, for example, isopropyl or tert-butyl.

[0231] In exemplary embodiments, the complex is represented by Formula II or Ila, and Ri, R5 and R9 are the same and each is a substituted phenyl. In some of these embodiments, one, two or each of Ri, R5 and R9 is a phenyl substituted by one or more alkyl, preferably lower alkyl(s) such as methyl or ethyl. In some of these embodiments, each of R1, R5 and R9 is mesityl. In some of any of these embodiments, at least one of R2-R4, Re-Rs and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl as defined herein such as, for example, isopropyl or tert-butyl.

[0232] In exemplary embodiments, the complex is represented by Formula II or Ila, and Ri, Rs and R9 are the same and each is an unsubstituted anthracenyl. In some of these embodiments, at least one of R2-R4, Re-Rs and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl as defined herein, such as, for example, isopropyl or tert-butyl.

[0233] In exemplary embodiments, the complex is represented by Formula III or Illa, and Ri, R5 and R9 are the same and each is a substituted naphthyl. In some of these embodiments, one, two or each of Ri, R5 and R9 is a naphthyl substituted by one or more alkyl(s), preferably lower alkyl(s) such as methyl or ethyl. In some of these embodiments, the naphthyl at R1, R5 and / or R9 is substituted by a lower alkyl (e.g., methyl) at the ortho position with respect to the attachment point to the naphthyl (representing X, Y or W). In some of any of these embodiments, R4, R8, R12, R13- R16, R17-R20 and R21-R24 are each hydrogen. Alternatively, at least one of R4, Rs, R12, R13-R16, R17-R20 and R21-R24 is an alkyl, for example, a lower alkyl such as methyl.

[0234] In exemplary embodiments, the complex is represented by Formula II or Ila, Ri is an unsubstituted phenyl, and Rs and R9 are each an alkyl, for example, a lower alkyl, preferably a lower bulky alkyl as described herein. In some of these embodiments, at least one of R2-R4, Rf>- Rs and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably each is a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms, which can be the same or different. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl such as, for example, isopropyl or tert-butyl. In exemplary embodiments, R3 is a lower alkyl such as methyl or ethyl and each of R7 and R11 is a bulky (e.g., branched) alkyl as defined herein, such as, for example, isopropyl or tert-butyl.

[0235] In exemplary embodiments, the complex is represented by Formula II or Ila, Ri and R5 are each an unsubstituted phenyl, and R9 is an alkyl, for example, a lower alkyl, preferably a lower bulky alkyl as described herein. In some of these embodiments, at least one of R2-R4, R6-R8 and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably each is a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms, which can be the same or different. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl as defined herein, such as, for example, isopropyl or tert-butyl. In exemplary embodiments, R3 and R7 are each independently a lower alkyl such as methyl or ethyl and R11 is a bulky (e.g., branched) alkyl as defined herein, such as, for example, isopropyl or tert-butyl. In exemplary embodiments, the complex is represented by Formula II or Ila, Ri is a substituted phenyl, and Rs and R9 are each an alkyl, for example, a lower alkyl, preferably a lower bulky alkyl as described herein. In some of these embodiments, Ri, is a phenyl substituted by one or more alkyl, preferably lower alkyl(s) such as methyl or ethyl. In some of these embodiments, Ri is mesityl. In some of these embodiments, at least one of R2-R4, R6-R8 and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably each is a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms, which can be the same or different. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl such as, for example, isopropyl or tert-butyl. In exemplary embodiments, R3 is a lower alkyl such as methyl or ethyl and each of R7 and R11 is a bulky (e.g., branched) alkyl such as, for example, isopropyl or tert-butyl.

[0236] In exemplary embodiments, the complex is represented by Formula II or Ila, Ri and R5 are each a substituted phenyl, which can be the same or different, and R9 is an alkyl, for example, a lower alkyl, preferably a lower bulky alkyl as described herein. In some of these embodiments, Ri and R5 are each independently a phenyl substituted by one or more alkyl, preferably lower alkyl(s) such as methyl or ethyl. In some of these embodiments, each of Ri and Rs is mesityl. In some of these embodiments, at least one of R2-R4, R6-R8 and R10-R12 is an alkyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is an alkyl, preferably each is a lower alkyl, of, e.g., 1 to 6, or 1 to 4, carbon atoms, which can be the same or different. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is methyl. In exemplary embodiments, at least one, or each, of R3, R7 and R11 is a bulky (e.g., branched) alkyl such as, for example, isopropyl or tert-butyl. In exemplary embodiments, R3 and R7 are each independently a lower alkyl such as methyl or ethyl and R11 is a bulky (e.g., branched) alkyl such as, for example, isopropyl or tertbutyl.

[0237] The organometallic complex as described herein in any of the respective embodiments is usable as a catalyst, or as a part of a catalyst system, for both the ring-opening polymerization of a cyclic ester or for the decomposition / degradation (e.g., via CRM) of a polyester, as described herein, and can be formed by mixing of an amine tris(phenolate) proligand of the form {NO3)h3 (see, Formulae IV, V, VI, Va and Via) and a metal reagent MX1X2X3X’, wherein X’ is as defined herein and each of Xi, X2 and X3 is independently a mono-anionic ligand as described herein, according to the following reaction:

[0238] Formula IV and MX1X2X3X’ wherein:

[0239] M and X’ are as defined herein and Xi, X2 and X3 are each independently a monoanionic ligand; and

[0240] Bl, B2, B3, X, Y and W are each as defined herein in any of the respective embodiments and any combination thereof.

[0241] In some of any of the embodiments described herein, M is zirconium or hafnium. Other tetravalent metals are also contemplated.

[0242] In some preferred embodiments, M is zirconium.

[0243] In some preferred embodiments, M is hafnium.

[0244] The monoanionic ligands, Xi, X2, X3 can be, as non-limiting examples, alkoxy, amide, alkyl, cycloalkyl, aryl, thioalkoxy, aryloxy, thioaryloxy, halo or amine, as these terms are defined herein.

[0245] According to some of any of the embodiments described herein, once the contacting is performed, the obtained complex can be employed without isolation or purification.

[0246] According to some of any of the embodiments described herein, X is a monoanionic ligand such as, but not limited to, alkyl, alkaryl, cycloalkyl, aryl, amide, alkoxy, thioalkoxy, aryloxy, thioaryloxy, halo or amine. When n is greater than 1, and X is present (e.g., z is 1), X in each fragment of the polynuclear complex can be the same or different.

[0247] According to some of any of the embodiments described herein, X’ is a neutral ligand such as, but not limited to, alkyl alcohol, aryl alcohol, aralkyl alcohol, and amine. When n is greater than 1, and X’ is present (e.g., q is 1), X in each fragment of the polynuclear complex can be the same or different.

[0248] According to some of any of the embodiments described herein, X and X’ form together a monoanionic bidentate ligand, as described herein.

[0249] According to some embodiments of any of the embodiments described herein, for example, for Formula A, Formula I or Formula II, as described herein, the ligand precursor is represented by Formula V :

[0250] wherein:

[0251] Bi, B2 and B3 are as defined herein in any of the respective embodiments; and

[0252] R1-R12 are each independently selected from hydrogen, alkyl, cycloalkyl, heteroalicyclic, aryl, heteroaryl, halo, alkoxy, and amino, or alternatively, two of R1-R4, and / or two of Rs-Rs, and / or two of R9-R12 independently form together a cyclic ring (fused to the phenolate ring), or are as described herein in any of the respective embodiments.

[0253] In preferred embodiments, at least one of R1-R12 is alkyl, cycloalkyl, aryl or heteroaryl, each independently being substituted or unsubstituted, or as described herein in any of the respective embodiments.

[0254] According to some embodiments of any of the embodiments described herein, for example, for Formula A, Formula I or Formula Ila, as described herein, the ligand precursor is represented by Formula VI: wherein

[0255] Ra, Rb, Re, Rf, Ri and Rj and R1-R12 are each as defined herein in any of the respective embodiments and any combination thereof.

[0256] According to some of any of the embodiments described herein, at least one, or each, of Ri, R5 and R9 is a substituted or unsubstituted aryl or heteroaryl.

[0257] According to some of any of the embodiments described herein, at least one, or each, of Ri, R5 and R9 is a substituted or unsubstituted alkyl, preferably a lower, non-bulky, alkyl (e.g., methyl, ethyl, and / or propyl).

[0258] According to some of any of the embodiments described herein, at least one of R2-R4, R6- Rs and R10-R12 is an alkyl, preferably a lower alkyl.

[0259] According to some of any of the embodiments described herein, the lower alkyl is a non- bulky lower alkyl (e.g., methyl, ethyl, and / or propyl).

[0260] According to some of any of the embodiments described herein, at least one, or each, of Ri, R5 and R9 is a substituted or unsubstituted aryl or heteroaryl, and m is 1.

[0261] According to some of these embodiments, M is a tetravalent group 4 metal (preferably zirconium), and in some embodiments, z is 1 and q is 0 or 1. In some of these embodiments, z and q are each 1, and the metal complex is represented by Formula II, Ila, III or Illa, as these are described herein in any of the respective embodiments and any combination thereof.

[0262] According to some embodiments of any of the embodiments related to Formulae Ila and Illa, n is 1, and the complex is a mononuclear complex.

[0263] According to some embodiments of any of the embodiments described herein, at least one, or each, of Ri, R5 and R9 is a substituted or unsubstituted alkyl, preferably a lower, non-bulky, alkyl (e.g., methyl, ethyl, and / or propyl), and m is 2.

[0264] According to some of these embodiments, M is a tetravalent group 4 metal (preferably zirconium), and z and q are each 0.

[0265] According to some of these embodiments, the metal complex is represented by Formula X or Formula XI:

[0266]

[0267] Formula XI wherein: the dashed line represents a covalent or a coordinative bond representing a bond between a donor atom and a metal; and

[0268] Bi, B2, B3 R1-R12, Ra, Rb, Re, Rf, Ri and Rj are each as defined herein in any of the respective embodiments, and can be the same or different in each ligand.

[0269] It is to be noted that while in Formulae X and XI, a dinuclear complex is presented, complexes of higher nuclearity are also contemplated, whereby Bi, B2, B3 R1-R12, Ra, Rb, Re, Rf, Ri and Rj can be the same or different in each ligand of the complex.

[0270] According to some embodiments of any of the embodiments described herein, the catalyst system consists of the organometallic complex as described herein in any of the respective embodiments and any combination thereof. According to some of these embodiments, the process comprises contacting the polyester or a composition comprising same with an organometallic complex as described herein in any of the respective embodiments and any combination thereof.

[0271] According to some of any of the embodiments described herein, the organometallic complex is formed in situ such that the contacting is with a catalyst system that comprises a ligand precursor as described herein in any of the respective embodiments, and a metal reagent, as described herein in any of the respective embodiments, that forms the organometallic complex with the ligand precursor. According to some of these embodiments, the catalyst system that comprises the ligand precursor (proligand) and the metal reagent, forms the organometallic complex in situ.

[0272] According to some of any of the embodiments described herein, the process comprises contacting the polyester or the composition comprising same with a catalyst system that comprises an amine tris(phenolate) proligand or ligand precursor of Formula IV, V, VI, Va or Via, as described herein in any of the respective embodiments and any combination thereof and optionally a metal reagent as described herein in any of the respective embodiments. According to some of these embodiments, the ligand precursor (proligand) and the metal reagent form the organometallic complex.

[0273] According to some of these embodiments, the metal reagent is represented by the formula M(X)z(Xi)w(X’)q, wherein: M is the transition metal as defined herein, w is 0 or an integer which together with z provides the valence number of the metal; X and X’ are each as defined herein and Xi is a monoanionic ligand, which can be the same or different from X, wherein when w is higher than 1, each Xi can be the same or different.

[0274] The metal reagent can alternatively be represented by the formula MX1X2X3X’, which corresponds to the formula M(X)z(Xi)w(X’)q when q is 1, w is 1, and z is two such that (X)z corresponds to X2 and X3.

[0275] The organometallic complex as described herein in any of the respective embodiments is also referred to herein as a “catalyst” or, in some embodiments, as a “pre-catalyst”, which is activated by a co-catalyst as described herein. In some of any of the embodiments described herein, the catalyst system further comprises a co-catalyst.

[0276] The “co-catalyst” described herein is also referred to herein and in the art as “initiator”.

[0277] In some embodiments the co-catalyst (initiator) is a hydroxy-containing compound.

[0278] According to some embodiments of any of the embodiments described herein, the polyester or the composition comprising same is contacted with the catalyst system as described herein in any of the respective embodiments and is further contacted with a hydroxy-containing compound. According to some of these embodiments, the polyester can be mixed with the hydroxy-containing compound and then contacted with the catalyst system, or the polyester can be contacted with the catalysts system and then with the hydroxy-containing compound, or the polyester can be contacted with the hydroxy-containing compound and the catalyst system at the same time.

[0279] According to some embodiments of any of the embodiments described herein, the hydroxycontaining compound is represented as HO-Rk, wherein Rk is alkyl, cycloalkyl or aryl, or, for example, HO-Rx-OH, wherein Rx is an alkylene, cycloalkylene, or arylene.

[0280] Exemplary hydroxy-containing compounds include, without limitation, benzyl alcohol, and alkyl alcohols such as ethyl alcohol, methyl alcohol, 2-propyl alcohol, 1 -hexanol, 1,4-benzene- dimethanol, 1,3,5-benzene-trimethanol, and poly(ethylene glycol).

[0281] The hydroxy-containing compound can feature two or more hydroxy groups, and such compounds are also referred to herein and in the art as polyhydroxy compounds.

[0282] In some of any of the embodiments described herein, the hydroxy-containing compound is represented by the formula Rk(OH)p, wherein p is an integer, for example, of from 2 to 10, or from 2 to 8, or from 2 to 6, and Rk is alkylene, cycloalkylene, alkarylene or arylene, or is a polymeric moiety.

[0283] Exemplary such compounds include, but are not limited to, alkylene glycols (featuring 2 hydroxy groups, for example, ethylene glycol, propylene glycol, etc., glycerols (featuring 3 hydroxy groups), higher linear saccharides, and polyhydroxy compounds such poly(ethylene glycol) or pentaerythritol.

[0284] According to some embodiments of any of the embodiments described herein, the hydroxycontaining compound is non-volatile (e.g. features a boiling temperature higher than 200, or higher than 300 °C). In some of these embodiments, the hydroxy-containing compound is non-volatile (e.g., substantially does not evaporate) under the reaction conditions as described herein (e.g., a condition that promotes degradation of the polyester in the presence of the organometallic complex, as described herein).

[0285] In some embodiments of any of the embodiments described herein, Rk is or comprises a polymeric moiety.

[0286] In exemplary embodiments, the polymeric moiety is or comprises a poly (alkylene glycol), for example, a poly (ethylene glycol). The poly (alkylene glycol) can be a linear polymer that features one terminal -OH group (such that in the other terminus the -OH is masked, and is, for example, -OR, wherein R is alkyl, cycloalkyl or aryl), or one that features two terminal -OH groups. Alternatively, the poly(alkylene glycol) can be a branched (e.g., starred) polymer, featuring 3 or more terminal -OH groups.

[0287] According to some of any of the embodiments described herein, the polymeric moiety in a hydroxy-containing compound is relatively short, such that the average molecular weight Mn of the polymer is lower than 2,000, preferably lower than 1,000, or lower than 800, or lower than 600, or lower than 500 grams / mol. In some embodiments, a hydroxy-containing polymer has an average molecular weight Mn in a range of from 100 to 2,000, or from 100 to 1,000, or from 100 to 800, or from 100 to 700, or from 100 to 600, or from 100 to 500, or from 200 to 1,000 or from 200 to 800, or from 200 to 700, or from 200 to 600, or from 200 to 500, grams / mol, including any intermediate values and subranges therebetween. According to some of these embodiments, the hydroxycontaining polymer features a boiling temperature higher than 200, or higher than 300 °C.

[0288] According to some embodiments of any of the embodiments described herein, the polymeric moiety in the hydroxy-containing compound is a poly(alkylene glycol), for example, poly(ethylene glycol) (PEG), which features an average molecular weight Mn as described herein in any of the respective embodiments. According to some of these embodiments, the poly(alkylene glycol) features a boiling temperature higher than 200, or higher than 300 °C.

[0289] According to some embodiments of any of the embodiments described herein, the condition for effecting the degradation comprises heating the mixture that comprises the polyester or the composition comprising the polyester, the catalyst system and the hydroxy-containing compound, if present.

[0290] According to some of any of the embodiments described herein, the heating is at a temperature at which the polyester is in a molten state.

[0291] In some of any of the embodiments described herein, the heating is at a high temperature, for example, higher than 100 °C, e.g., between 100 °C and 200 °C, or between 120 °C and 200 °C, for example, at about 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C or 180 °C.

[0292] In some of any of the embodiments described herein, the heating is at a temperature at which the cyclic ester and / or the polyester are in a molten state, namely, higher by at least 10, or at least 20 °C than the melting temperature of the polyester, for example, at about 180 °C.

[0293] In some embodiments of any of the embodiments described herein, subjecting to the condition (e.g., heating) is for a time period that ranges from 5 minutes to 24 hours, or from 10 minutes to 24 hours, or from 10 minutes to 12 hours, or from 10 minutes to 6 hours, or from 10 minutes to 3 hours, or from 30 minutes to 3 hours, including any intermediate values and subranges therebetween.

[0294] In some embodiments of any of the embodiments described herein, subjecting to the condition (e.g., heating) is performed without any solvent.

[0295] In some embodiments of any of the embodiments described herein, subjecting to the condition (e.g., heating) is in a solution (e.g., in an organic solvent), such that the mixture that comprises the polyester or the composition comprising the polyester, the catalyst system and the hydroxy-containing compound, if present, further comprises an organic solvent. An exemplary organic solvent is toluene, although any other organic solvents are contemplated. In some embodiments, the organic solvent is devoid of heteroatoms that can coordinate with the metal atom, such as oxygen and nitrogen. In some embodiments, the organic solvent is such that the polyester and / or the formed cyclic ester are soluble therein.

[0296] Exemplary solvents include, but not limited to, dichloromethane (DCM), chlorobenzene, tetrahydrofuran (THF), diethylether, ethylene dichloride, toluene, pentane, and the like.

[0297] In some of any of the embodiments described herein, subjecting to the condition (e.g., heating) is in a melt, that is, is devoid of a solvent and is performed at a temperature at which the polyester is liquid, for example, at a temperature which is at least the melting temperature of the polyester, or is higher than the melting temperature of the polyester by, for example, 5, 10, 15, 20 or more °C.

[0298] In some of any of the embodiments described herein, a mol ratio between the number of the cyclic ester units in the polyester and the organometallic complex ranges from 1000: 1 to 2000000: 1, or from 3000: 1 to 2000000: 1, or from 10000: 1 to 1000000: 1, or from 20000: 1 to 200000: 1, including any intermediate values and sub-ranges therebetween.

[0299] In some of any of the embodiments described herein, a mol ratio of the organometallic complex and the hydroxy -containing compound (if present) ranges from 1000: 1 to 1: 1000, or from 100: 1 to 1: 100, or from 10: 1 to 1: 1000, or from 10: 1 to 1: 100, or from 10: 1 to 1:50, or from 10: 1 to 1 :40 or from 10: 1 to 1:30, or from 10: 1 to 1 :20 or from 10: 1 to 1 : 10, or from 1 : 1 to 1 : 10, or from 1: 1 to 1:8, or from 1: 1 to 1:6, or from 1: 1 to 1:5 or from 1: 1 to 1:4, including any intermediate values and subranges therebetween.

[0300] In some of any of the embodiments described herein, subjecting to the condition (e.g., heating) is effected under inert environment.

[0301] By “inert environment” it is meant an environment that is substantially free of oxygen, carbon dioxide, water and / or any other substances that may chemically react with the organometallic complex or otherwise interfere with the de-polymerization reaction.

[0302] According to some of any of the embodiments described herein, the reaction mixture (comprising the polyester or a composition comprising a polyester, the catalyst system and optionally the hydroxy-containing compound) is exposed to aerobic environment prior to subjecting to the condition, such that the contacting is effected, at least in part, under aerobic (noninert) environment.

[0303] According to some of any of the embodiments described herein, the reaction mixture (comprising the polyester or a composition comprising a polyester, the catalyst system and optionally the hydroxy-containing compound) is exposed to water or to a humid environment prior to subjecting to the condition (e.g., during the contacting). In some embodiments, the humid environment is an aerobic environment and the reaction mixture (comprising the polyester or a composition comprising a polyester, the catalyst system and optionally the hydroxy-containing compound) is exposed to water molecules present in the aerobic environment, for example, at a concentration of at least 3 grams / m2, from example, from 3 to 30, or from 3 to 20, or from 3 to 15, or from 3 to 12, or from 3 to 10, or from 3 to 8, or from 3 to 5, grams / 2.

[0304] According to some of any of the embodiments described herein, the process further comprises, subsequent to subjecting to the condition (e.g., heating) as described herein, separating the obtained cyclic ester from the reaction mixture.

[0305] According to some of any of the embodiments described herein, the separating is by sublimating the cyclic ester and collecting it as a solid product. By “sublimating” it is meant heating the reaction mixture to a temperature above the boiling temperature of the cyclic ester, in the presence of a collecting device that features a temperature lower than a melting point of the cyclic ester, for example, lower by at least 10, at least 20, or at least 30, or at least 50, °C, than a melting point of the cyclic ester. Once the vapors of the heated cyclic ester contact the collecting device, the cyclic ester solidifies and collected as a solid. The sublimating can be performed under reduced pressure and / or in the presence of a gas flow that carries the vapors of the cyclic ester to the cold collecting device.

[0306] Alternatively, the separating comprises distillation of the formed cyclic ester from the reaction mixture, for example, by distillation under reduced pressure.

[0307] The separation can include, alternatively, or in addition, treating the obtained product by other common work-up procedures such as washing or immersing in water and / or an organic solvent, column chromatography; etc.

[0308] The process as described herein is a CRM process in which a polyester is decomposed or degraded into the cyclic ester monomers that form the polyester, that is, to a plurality of cyclic ester molecules that are bound together via ester bonds in the polymer, or to a plurality of cyclic ester molecules that were polymerized to form the polyester. The chemical decomposition of the polyester into the cyclic ester units that compose it can be considered as a hydrolysis of the polyester.

[0309] The term “cyclic ester” as used herein and in the art describes a -C(=O)-O-Rx in which Rx is a hydrocarbon chain (e.g., lower, medium or higher alkyl, optionally substituted), as defined herein, optionally interrupted by one or more heteroatoms or moieties as defined herein, wherein one carbon atom of the hydrocarbon chain (e.g., of an alkyl) is linked to the carbon atom of the carboxylate to form a ring.

[0310] The cyclic ester as described herein defines both, the polyester formed of the cyclic ester and subjected to the CRM process as described herein in any of the respective embodiments and the cyclic ester obtained by the process (and which can thereafter be subjected to ring opening polymerization to thereby provide a polyester).

[0311] In some embodiments, a cyclic ester can be represented by Formula XII:

[0312] Formula XII wherein:

[0313] Yi and Y2 are each independently selected from oxygen and sulfur; and

[0314] L is a hydrocarbon chain, for example, a hydrocarbon chain which comprises one or more alkylene chains, each optionally being independently substituted or unsubstituted, and which can optionally be interrupted therebetween by one or more moieties such as oxygen atom, sulfur atom, amine, silyl, carbonyl, amide, carboxy (-C(=O)-O-), thiocarboxy, thiocarbonyl, and the like.

[0315] Each alkylene chain can be of from 1 to 30 carbon atoms, preferably from 1 to 20 carbon atoms, or from 1 to 15 carbon atoms, or from 1 to 10 carbon atoms.

[0316] In some of any of the embodiments described herein, the cyclic ester comprises two or more alkylene chains, which are interrupted therebetween, wherein at least two alkylene chains are interrupted therebetween by a carboxy group. Such cyclic esters are also referred to herein and in the art as “cyclic diesters”.

[0317] In some of any of the embodiments described herein, the one or more alkylene chain(s) is / are unsubstituted.

[0318] In some of any of the embodiments described herein, at least one of Y 1 and Y2 is oxygen.

[0319] In some of any of the embodiments described herein, each of Yi and Y2 is oxygen.

[0320] In some of any of the embodiments described herein, L is an alkylene chain, noninterrupted. Such cyclic esters are also referred to herein and in the art as “lactone”.

[0321] In some of any of the embodiments described herein, L comprises two alkylene chains, interrupted by a carboxy group, whereby the two alkylene chains are identical to one another. Such a cyclic diester can also be regarded as a di-lactone of two molecules of a 2-hydroxycarboxylic acid, and is also referred to in the ait as lactide.

[0322] While the term “lactide” generally describes a dilactone of any 2-hydroxycarboxylic acid, herein and in the art, this term typically also refers to a cyclic di-ester (di-lactone) of lactic acid (2- hydroxypropionic acid), as shown, for example, in Scheme 1 hereinabove and in Background Art. FIG. 1.

[0323] Cyclic esters usable in the context of the present embodiments include substituted and unsubstituted lactones such as, for example, caprolactones and lactides, although any other cyclic esters are contemplated, for example, glycolide, 5-valerolactone, y-butyrolactone, s-caprolactone, co-pentadecalactone, cyclopentadecanone, 16-hexadecanolide, oxacyclotridecan-2-one.

[0324] In some embodiments of any of the embodiments described herein, the cyclic ester is a lactide, and the polyester is or comprises poly(lactic acid) (PLA), for example, the polyester is a copolymer that comprises backbone units of lactide and backbone units of one or more other cyclic ester(s), or a block copolymer that comprises at least one block made of lactide monomers.

[0325] In some embodiments of any of the embodiments described herein, the cyclic ester is a lactide, and the polyester is poly (lactic acid) (PLA).

[0326] In some embodiments of any of the embodiments described herein, the cyclic ester has a chiral center.

[0327] Herein a “chiral cyclic ester” or a “cyclic ester having a chiral center”, typically describes a cyclic ester or a cyclic diester as defined herein, in which one or more carbon atoms in one or more of the alkylene chains is substituted and thereby form a chiral center. Whenever these phrases are used, the cyclic ester can be one enantiomer, one diastereomer, a meso form, or a racemic mixture, unless otherwise indicated.

[0328] In some of any of the embodiments described herein, the cyclic ester is lactide, that is, a dilactone of lactic acid (2-hydroxypropionic acid).

[0329] In some of any of the embodiments described herein, the cyclic ester is a lactone, for example, a caprolactone such as s-caprolactone.

[0330] According to exemplary embodiments of the present invention, the polyester is or comprises a poly(lactic acid) (PLA), that is formed of a plurality of lactides and comprises a plurality of backbone units derived from lactide.

[0331] In some of any of the embodiments described herein, the cyclic ester that forms the polyester PLA is lactide and the lactide is a homochiral lactide (L-lactide or D-lactide) or a racemic lactide (rac-lactide) or a meso-lactide, or any mixture thereof. In some of any of the embodiments described herein, the lactide is a homochiral L-lactide. In some of these embodiments, the polyester is an isotactic polyester (an isotactic poly(lactic acid); PLA).

[0332] In some of any of the embodiments described herein, the lactide is a racemic lactide (rac- lactide). In some of these embodiments, the polyester is a heterotactic polyester (a heterotactic PLA).

[0333] In some of any of the embodiments described herein, the lactide is a meso-lactide. In some of these embodiments, the polyester is a syndiotactic polyester (a syndiotactic PLA).

[0334] In some of any of the embodiments described herein, the lactide comprises a mixture of two lactides, for example, a mixture of a homochiral lactide (L-lactide or D-lactide) and meso- lactide, or a mixture of a homochiral lactide (L-lactide or D-lactide) and rac-lactide, and the polyester is a heterochiral PLA copolymer.

[0335] The various lactides composing the polyester copolymer can be randomly distributed along the polyester chain, forming a stereo-irregular polyester (e.g., PLA) copolymer, or can be form a block copolymer of a cyclic ester.

[0336] Herein, the phrase “block copolymer of a cyclic ester” is also referred to herein interchangeably as “block polyester copolymer” and describes block copolymers comprised of two or more blocks, wherein at least two of these blocks comprise, each independently, a polyester homopolymer, wherein the polyester homopolymers in these at least two blocks differ from one another by their chemical composition and / or stereoconfiguration.

[0337] In some embodiments, each block that comprises a polyester homopolymer is comprised of polymerized monomers of a corresponding cyclic ester, and is also referred to herein as a unit in the block copolymer.

[0338] Each block is formed of a plurality of cyclic ester monomers which represent a plurality of repeating backbone units covalently attached to one another and forming the homopolymer block.

[0339] The term “block” is also referred to herein as “homopolymer block”, “homopolyester block”, “polyester block”, “polyester unit”, “unit” and “unit comprising polymerized monomers of a cyclic ester” (as indicated), and also as combinations of any of the foregoing, and is meant to encompass a unit in the block copolymer that is made of one type of polyester, that is, of polymerized monomers of one type of cyclic ester (all having the same chemical composition and stereoconfiguration).

[0340] A block polyester copolymer can comprise two, three, four, five or more blocks, and at least two of these blocks are homopolyester blocks which differ from one another by the type (stereoconfiguration and / or chemical composition) of the monomers of the cyclic esters that are polymerized within the block, as described herein.

[0341] A block polyester copolymer can comprise two types of blocks (units), each independently comprising (or composed of) a plurality of polymerized monomers of a cyclic ester, at least one of these units comprises a plurality of polymerized monomers of a first cyclic ester, and at least one another unit of these units comprises a plurality of polymerized monomers of a second cyclic ester, the second cyclic ester differing from the first cyclic ester by a stereoconfiguration and / or a chemical composition, as defined herein.

[0342] A block polyester copolymer which comprises two types of blocks can comprise 2, 3, 4, 5 or more blocks (units), in an alternating order, such that in any pair of adjacent blocks (units), the units are made of polymerized monomers of a different cyclic ester.

[0343] A block polyester copolymer can comprise three or more types of blocks (units), each independently comprising (or composed of) a plurality of polymerized monomers of a cyclic ester, at least one of these units comprises a plurality of polymerized monomers of a first cyclic ester, and at least one another unit of these units comprises a plurality of polymerized monomers of a second cyclic ester, the second cyclic ester differing from the first cyclic ester by a stereoconfiguration and / or a chemical composition, as defined herein. Such a block copolymer can comprise in addition to the above-mentioned units of the first and second cyclic ester, units which are not polymerized monomers of a cyclic ester (e.g., are rather made of repeating backbone units of monomers which are not a cyclic ester). Alternatively, such a block copolymer can comprise, in addition to the above-mentioned units of the first and second cyclic ester, one or more types of blocks (units), each independently comprising (or composed of) a plurality of polymerized monomers of a third cyclic ester, and optionally of a fourth cyclic ester, while the third cyclic ester is different from the first, second and, if present, the fourth cyclic esters, and the fourth cyclic ester is different from the first, second and third cyclic esters.

[0344] A block polyester copolymer can comprise at least two types of blocks (units), at least one of these units comprising (or composed of) a plurality of polymerized monomers of a cyclic ester, for example, a lactide, at least one of these units comprises a plurality of polymerized monomers of a second cyclic ester, differing from the first cyclic ester by a chemical composition (e.g., a cyclic ester other than lactide), and / or of at least one of these units comprises a plurality of polymerized monomers that are not of a cyclic ester (e.g., are rather made of repeating backbone units of monomers which are not a cyclic ester).

[0345] A block polyester copolymer can comprise three or more types of blocks (units), each independently comprising (or composed of) a plurality of polymerized monomers of a cyclic ester, at least one of these units comprises a plurality of polymerized monomers of a first cyclic ester such as lactide, and at least one another unit of these units comprises a plurality of polymerized monomers of a second cyclic ester, the second cyclic ester differing from the first cyclic ester by a stereoconfiguration and / or a chemical composition, as defined herein. Such a block copolymer can comprise in addition to the above-mentioned units of the first and second cyclic ester, units which are not polymerized monomers of a cyclic ester (e.g., are rather made of repeating backbone units of monomers which are not a cyclic ester). Alternatively, such a block copolymer can comprise, in addition to the above-mentioned units of the first and second cyclic ester, one or more types of blocks (units), each independently comprising (or composed of) a plurality of polymerized monomers of a third cyclic ester, which is other than lactide, and optionally of a fourth cyclic ester, while the third cyclic ester is different from the first, second and, if present, the fourth cyclic esters, and the fourth cyclic ester is different from the first, second and third cyclic esters.

[0346] Whenever there are more than two types of blocks (units) in the block polyester copolymer, these different blocks can be arranged in any order.

[0347] Non-limiting examples of block copolymers include: A-B; A-B-A; B-A-B-A-B; A-B-C; A-B-C-B-A; A-B-C-D; A-B-C-D-C-B-A; -A-B-A-B-A-B-A-B- ; -A-B-C-A-B-C-A-B-C-; -A-B- A-C-A-B-A-C-; -A-B-C-B-A-C-B-C-; -A-B-C-D-A-B-C-D-; and -A-C-D-A-B-C-A-D-C-, wherein A, B, C and D are each independently a different block, for example, A is a first type of block (a first unit) made of polymerized monomers of a cyclic ester of a first type (a first cyclic ester); B is a second type of block (a second unit) made of polymerized monomers of a cyclic ester of a second type (a second cyclic ester); C is a third type of block (a third unit) made of polymerized monomers of a cyclic ester of a third type (a third cyclic ester), or, alternatively, is a block made of polymerized monomers which are not a cyclic ester; and D is a fourth type of block (a fourth unit) made of polymerized monomers of a cyclic ester of a fourth type (a fourth cyclic ester), or, alternatively, is a block made of polymerized monomers which are not a cyclic ester and which different from C.

[0348] In some embodiments, the block copolymer is comprised of two types of blocks, for example, is comprised of a polymer sequence of Blockl-Block2, or Blockl-Block2-Blockl, or Blockl-Block2-Blockl-Block2, wherein Blockl is a polyester of first chemical composition and / or stereoconfiguration and Block2 is a polyester of a second chemical composition and / or stereoconfiguration which is different from the first chemical composition and / or stereoconfiguration.

[0349] The copolymer, according to these embodiments, can be a diblock, triblock, tetrablock, etc. By “diblock”, “triblock”, “tetrablock”, etc., the number of blocks is presented. These types of blocks in each of such block copolymers are at least two, regardless of the number of blocks.

[0350] When a block copolymer as described herein comprises two units, it is referred to as a diblock copolymer.

[0351] When a block copolymer as described herein comprises three units (two of which can the same or all three are different), it is referred to as tri-block copolymer.

[0352] When a block copolymer as described herein comprises four units (two or three of which can be the same or all four are different), it is referred to as tetra-block copolymer, and so forth.

[0353] Herein throughout, the term “chemical composition” refers to the chemical structure of the cyclic ester, that is, the type of atoms and their 2D arrangement.

[0354] Herein throughout, the term “stereoconfiguration” refers to the spatial arrangement of the atoms in the cyclic ester, and thus refers to cyclic ester monomers featuring one or more chiral centers. According to some embodiments, the polymerized monomers feature a stereoconfiguration according to the stereoconfiguration of the chiral center(s).

[0355] For example, the cyclic monomer can be an enantiomer, and the polymerized monomers feature an isotactic configuration of the enantiomer. Thus, if a first and a second cyclic ester differ from one another by being different enantiomers, a unit comprising polymerized monomers of the first cyclic ester exhibits an isotactic stereoconfiguration of this enantiomer, and a unit comprising polymerized monomers of the second cyclic ester exhibits an isotactic stereoconfiguration of this other enantiomer.

[0356] For example, the cyclic monomer can be a diastereoisomer, and the polymerized monomers feature an isotactic configuration of the diasteroisomer. Thus, if a first and a second cyclic ester differ from one another by being different diastereomers, a unit comprising polymerized monomers of the first cyclic ester exhibits an isotactic stereoconfiguration of this diastereomer, and a unit comprising polymerized monomers of the second cyclic ester exhibits an isotactic stereoconfiguration of this diastereomer.

[0357] In another example, a first cyclic ester is an enantiomer or a diastereomer and a second cyclic ester is a racemic mixture, a unit comprising polymerized monomers of the first cyclic ester exhibits an isotactic stereoconfiguration of the enantiomer or diastereomer, and a unit comprising polymerized monomers of the second cyclic ester exhibits a racemic mixture of the two isotactic stereoconfigurations of the enantiomer or diastereomer. A block comprised of such racemic cyclic ester can be heterotactic, isotactically-inclined, gradient isotactic or even atactic.

[0358] Block polyester copolymers featuring at least two units in which the first and second cyclic esters differ in their stereoconfiguration are also referred to herein as “stereoblocks”. In exemplary embodiments, the block copolymer is made of two or more types of lactides, which differ from one another in stereoconfiguration.

[0359] Exemplary such block copolymers include, but are not limited to: PLLA-PDLA, PDLA- PLLA-PDLA, PDLA-PLLA-PDLA-PLLA, and so forth.

[0360] According to some embodiments of any of the embodiments described herein, the cyclic ester is or comprises a lactide, and the polyester is or comprises a poly(lactic acid) (PLA). The polyester can be a homopolymer, in which all of the repeating units feature the same chemical composition and stereoconfiguration, or a PLA copolymer (e.g., a block copolymer), which is made of at least two types of lactides that differ from one another at least by their stereoconfiguration, as described herein in any of the respective embodiments and any combination thereof, and / or which is made of one or more types of lactide and one or more types of another cyclic ester and optionally one or more type of different polymerized monomers.

[0361] According to some embodiments of any of the embodiments described herein, the CRM process as described herein is stereoselective, such that, for example, at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the obtained cyclic ester features substantially the same stereoconfiguration as the backbone (repeating) units of the polyester (e.g., which is formed by ROP of the cyclic ester).

[0362] According to some of any of the embodiments described herein, when the polyester is a homopolymer, in which all of the backbone units feature the same chemical composition and stereoconfiguration, at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the obtained cyclic ester features substantially the same stereoconfiguration as the backbone (repeating) units of the polyester homopolymer.

[0363] For example, if the polyester is poly(L-lactic acid) (PLLA), at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the obtained cyclic ester is L-lactide.

[0364] According to some embodiments of any of the embodiments described herein, the polyester is a poly(lactic acid) copolymer as described herein in any of the respective embodiments, which is made of at least two of a homochiral lactide (e.g., L-lactide and / or D-lactide), a racemic lactide and / or a meso-lactide, and at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the lactide obtained in the process features the same stereoconfiguration as the backbone units of the polyester.

[0365] According to some embodiments of any of the embodiments described herein, the polyester is a poly(lactic acid) block copolymer as described herein in any of the respective embodiments, which comprises at least two blocks that differ from one another by the chemical composition and / or stereoconfiguration, as described herein, and at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the lactide obtained in the process features the same stereoconfiguration as the backbone units of the polyester.

[0366] According to some embodiments of any of the embodiments described herein, the composition consists of a polyester, for example, PLA. In some of these embodiments, the composition can consist essentially of one type of a PLA, for example, PLLA. In some of any of these embodiments, at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the lactides obtained in the process feature the same stereoconfiguration as the backbone units of the polyester, for example, L-lactide. The remaining lactides can be meso-lactide and / or rac-lactide.

[0367] According to some embodiments of any of the embodiments described herein, the composition consists of two or more types of PLA, for example, two or more of PLLA, PLDA, and a multi-block (e.g., di-block, tri-block) PLA copolymer as described herein in any of the respective embodiments. In some of these embodiments, at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the lactides obtained in the process feature the same stereoconfiguration as the backbone units of these polyesters.

[0368] According to some embodiments of any of the embodiments described herein, the CRM process as described herein is selective to polyesters, that is, polymeric materials other than a polyester do not undergo decomposition or degradation or CRM, during the process.

[0369] According to some of any of the embodiments described herein, the composition comprises, in addition to a polyester (or two or more types of a polyester), polymeric materials other than the polyester. According to some of any of these embodiments, the polyester undergoes degradation to the cyclic ester(s) forming same, whereby the other polymeric materials remain intact or do not undergo decomposition, degradation or CRM. According to some of these embodiments, at least 90 %, or at least 95 %, or at least 98 %, or all, of the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of the cyclic ester. According to these embodiments, the process is selective towards decomposition of a polyester and not towards decomposition of the other polymeric materials that can be present in the composition.

[0370] According to some of any of the embodiments described herein, the composition that comprises the polyester comprises a polyester copolymer, made of two or more types of a polyester, that differ from one another by the chemical composition and / or stereoconfiguration. According to some of any of these embodiments, the polyester copolymer undergoes degradation to the cyclic ester(s) forming same. According to some of these embodiments, at least 90 %, or at least 95 %, or at least 98 %, or all, of the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of the two or more types of cyclic ester.

[0371] According to some of any of the embodiments described herein, the process is selective towards polyesters other than poly(caprolactone) (PCL). According to some of these embodiments, when the polyester is a copolymer of two of more types of cyclic esters, none of the cyclic esters is a lactone.

[0372] According to some of any of the embodiments described herein, the composition that comprises the polyester comprises a polyester block copolymer, made of two or more types of units or blocks, and at least one of the units comprises a plurality of polymerized monomers of a first cyclic ester, for example, a plurality of polymerized monomers of a lactide or of a cyclic ester other than lactone. The other one or more blocks can be made of a plurality of polymerized monomers of a second cyclic ester (including a lactone) that differ from the first cyclic ester by the chemical composition and / or stereoconfiguration and / or of other monomers which are not a cyclic ester. According to some of any of these embodiments, the polyester block copolymer undergoes degradation to the cyclic ester(s) at least the blocks made of the polymerized first cyclic ester. For example, a block copolymer comprises one or more units of PLA and one or more units of a cyclic ester other than PLA, and the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of the two or more types of cyclic ester. For example, a block copolymer comprises one or more units of PLA and one or more units of a cyclic ester which is lactone, and the obtained cyclic ester comprises the lactide, the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of the lactide. For example, a block copolymer comprises one or more units of PLA and one or more units of a polymer formed of monomers that are not cyclic ester, and the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of lactide.

[0373] According to some embodiments of any of the embodiments described herein, the CRM process as described herein is selective to poly(lactic acid), that is, polymeric materials other than PLA, including polyesters other than PLA, do not undergo decomposition or degradation or CRM, during the process. According to some of these embodiments, at least 90 %, or at least 95 %, or at least 98 %, or all, of the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of a lactide, or a mixture of two or more lactides, depending on the chemical composition of the PLA. According to some of these embodiments, the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) does not include a cyclic ester other than lactide, or includes less than 10 %, or less than 8 %, or less than 5 %, or less than 3 %, or less than 1 %, or less than 0.1 %, of a cyclic ester or a mixture of two or more types of cyclic esters other than lactide. According to these embodiments, the process is selective towards decomposition of PLA and not towards decomposition of the other polymeric materials, including other polyesters, that can be present in the composition.

[0374] According to some embodiments of any of the embodiments described herein, the CRM process as described herein does not include decomposition of a polycaprolactone (PCL), for example, of poly(epsilon-caprolactone), such that when a composition that comprises the polyester comprises PCL, the PCL does not undergo decomposition or degradation or CRM, during the process. According to some of these embodiments, the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) does not include a lactone, or includes less than 10 %, or less than 8 %, or less than 5 %, or less than 3 %, or less than 1 %, or less than 0.1 %, of a lactone or mixtures of lactones that form the PCL.

[0375] According to some embodiments of any of the embodiments described herein, the composition comprises two or more types of a polyester, for example, PLA and one or more additional polyesters made of glycolide, 5- valerolactone, y-butyrolactone, s-caprolactone, co- pentadecalactone, cyclopentadecanone, 16-hexadecanolide, and / or oxacyclotridecan-2-one. According to some of these embodiments, at least 90 %, or at least 95 %, or at least 98 %, or all, of the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of a lactide, or a mixture of two or more lactides, depending on the chemical composition of the PLA. According to some of these embodiments, the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) does not include any of these cyclic esters which are other than lactide, or includes less than 10 %, or less than 8 %, or less than 5 %, or less than 3 %, or less than 1 %, or less than 0.1 %, of these cyclic esters or a mixture of two or more types of these cyclic esters other than lactide.

[0376] According to some embodiments of any of the embodiments described herein, the composition comprises two or more types of a polyester, for example, PLA and one or more additional polyesters made of a cyclic ester other than lactone, for example, glycolide, cyclopentadecanone, 16-hexadecanolide, and / or oxacyclotridecan-2-one. According to some of these embodiments, at least 90 %, or at least 95 %, or at least 98 %, or all, of the product obtained by the process (a product that is separated from the reaction mixture by e.g., sublimation or distillation) consist of these cyclic esters, depending on the chemical composition of the polyester. The composition as described herein in any of the respective embodiments can be derived from various polyester-containing sources, or PLA-containing sources, including industrial compositions or articles-of-manufacture and consumer compositions or articles-of-manufacture, which comprise, in at least a part or a portion thereof, a polyester, for example, PLA. In some embodiments, the composition can be an article-of-manufacturing, such as, for example, a consumed product, or a product used or obtained in an industrial process, or a part thereof. The article-of-manufacturing or a part thereof can be included in the composition used in the process per se, or upon separating a relevant part of the article-of-manufacturing and / or pre-treating the article-of-manufacturing before subjecting it to the CRM process. For example, the article-of- manufacturing or the portion thereof can be washed or immersed in water and / or an organic solvent, so as to remove materials or impurities that may adversely affect the activity of the catalyst system or otherwise interfere with the CRM process, and / or that may adversely affect the purity of the obtained cyclic ester product (e.g., materials that cannot be readily separated from the cyclic ester product).

[0377] The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA blended or compounded with other polymers or fillers. Non-limiting examples include PLA-starch blends such as commonly used in biodegradable films and packaging, or the film or package containing such blends; PLA reinforced with natural fibers such as cellulose, flax, or hemp, or articles-of-manufacturing or parts thereof made of such reinforced PLA; PLA-polymer blends or alloys such as PLA / PBAT, PLA / PBS; Laminated or coated articles in which PLA is combined with barrier layers (e.g., EVOH, PVOH).

[0378] The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA, which form a part or used in disposable packaging and consumer products, for example, high-volume, short-lifetime PLA products. Nonlimiting examples include food service items such as cups, trays, bottles, cutlery, and lids; flexible films, shrink wraps, and thermoformed containers; single-use blister packs or wrappers; 3D- printed objects manufactured from PLA filament.

[0379] The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA, which form a part or contitute biomedical and pharmaceutical devices. Non-limiting examples include medical-grade PLA-containing compositions and articles such as biodegradable surgical sutures and meshes; implantable scaffolds, pins, and fixation devices; drug-eluting PLA microspheres and films; and PLA-based tissue engineering substrates. The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA, which are or which are derived from industrial waste. For example, the CRM process can be applied to clean manufacturing scrap from Injection molding processes; thermoforming lines; and 3D printing operations, including support structures and misprints.

[0380] The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA, which further incorporate pigments, fillers, and / or performance additives (e.g., calcium carbonate, talc, UV stabilizers). None limiting examples include colored containers and decorative items; glow-in-the-dark or metallic PLA parts; mineral-reinforced PLA sheets or films.

[0381] The CRM process as described herein is applicable to compositions or articles-of- manufacturing comprising a polyester such as PLA, employed in agricultural and horticultural Applications. Non-limiting examples include field-deployed PLA articles such as biodegradable mulch films; seedling trays and nursery pots; plant clips, labels, and stakes. Although partially degraded or soil-contaminated, these items can be collected and processed via CRM in centralized facilities, allowing the conversion of degraded PLA into valuable monomeric precursors.

[0382] According to some embodiments of any of the embodiments described herein, the polyester (e.g. PLA) in the composition that undergoes the CRM process is prepared from a cyclic ester (e.g., a lactide) by ring opening polymerization (ROP), using a suitable catalyst, for example, catalysts known in the art as usable in ROP of a cyclic ester such as lactide (e.g., tin octanoate). In exemplary embodiments, the polyester is prepared by ROP performed using a complex or a catalyst system as described herein in any of the respective embodiments. In exemplary embodiments, the polyester is prepared by ROP performed using a complex or a catalyst system or a process as described in WO 2023 / 053128 and WO 2023 / 053127. In exemplary embodiments, the polyester is prepared by ROP performed using a complex or a catalyst system or a process as described in WO 2017 / 137990.

[0383] The polyester as described herein in any of the respective embodiments (e.g., PLA), can have an average molecular weight Mn in a range of from 1,000 to 1,000,000 grams / mol, or from 1,000 to 500,000 grams / mol, or from 1,000 to 200,000 grams / mol, or from 10,000 to 1,000,000 grams / mol, or from 10,000 to 500,000 grams / mol, or from 10,000 to 200,000 grams / mol or from 10,000 to 100,000 grams / mol, including any intermediate values and subranges therebetween. Higher molecular weights are also contemplated.

[0384] Herein throughout, unless otherwise indicated, molecular weight and its distribution are determined by GPC, for example, as described in the Examples section that follows. Herein throughout, unless otherwise indicated, a “polyester” encompasses a homopolymer, made of one type of a cyclic ester, a polyester copolymer, made of two of more types of cyclic esters, which differ from one another by the chemical composition and / or stereoconfiguration, as described herein, and a block copolymer, which comprises at least one unit made of a cyclic ester or two or more types of cyclic esters, as described herein.

[0385] According to some embodiments of any of the embodiments described herein, the polyester (e.g. PLA) is prepared from a cyclic ester (e.g., a lactide) by ring opening polymerization (ROP) using an organometallic complex or a catalyst system that forms the organometallic complex as described herein, as described, for example, in WO 2023 / 053128 and WO 2023 / 053127, and as such, contains at least residual amounts of the organometallic complex.

[0386] According to these embodiments, the composition that comprises the polyester further comprises the organometallic complex. The composition may comprise the polyester obtained by the ROP, or a composition or article-of-manufacturing or a part thereof that comprises the polyester obtained by the ROP using an organometallic complex or a catalyst system that forms the organometallic complex as described herein.

[0387] According to some of these embodiments, the composition that comprises the polyester is already contacted with the organometallic complex and the CRM process as described herein comprises subjecting the composition to the condition that effects degradation of the polyester, as described herein in any of the respective embodiments.

[0388] According to some of these embodiments, contacting the composition that comprises the polyester with the organometallic complex or with a catalyst system that forms the organometallic complex has been effected while preparing the polyester, such that the process comprises subjecting a composition that comprises a polyester and the organometallic complex used to prepare it to the condition that effects degradation of the polyester, as described herein in any of the respective embodiments.

[0389] According to some of these embodiments, subjecting to the condition is performed during a time period that ranges from 1 day to 720, or from 1 to 365, or from 1 to 200, days, including any intermediate values and subranges therebetween, after the polyester is prepared in the presence of the organometallic complex.

[0390] According to some of any of these embodiments, the process further comprises, prior to subjecting to the condition that effects degradation as described herein, contacting the composition with a metal reagent as described herein in any of the respective embodiments, which can reactivate or enhance the activity of the organometallic complex. According to some of these embodiments, an amount of the metal reagent may correspond to a mol ratio relative to the organometallic complex that ranges from 10: 1 to 1: 10, including any intermediate values and subranges therebetween.

[0391] According to some of any of these embodiments, the process further comprises, prior to subjecting to the condition that effects degradation as described herein, contacting the composition with a hydroxy-containing compound as described herein in any of the respective embodiments, which can enhance the activity of the organometallic complex. The amount of the hydroxycontaining compound can be as described herein in any of the respective embodiments.

[0392] According to some of any of these embodiments, the process further comprises, prior to subjecting to the condition that effects degradation as described herein, contacting the composition with a metal reagent and with a hydroxy-containing compound as described herein in any of the respective embodiments.

[0393] According an aspect of some embodiments of the present invention, there is provided a cyclic ester obtained by a process as described herein, for example, a lactide or a mixture of one or more lactides, or a mixture of two or more cyclic esters, for example, a lactide and another cyclic ester, as described herein in any of the respective embodiments and any combination thereof, according to the chemical composition of the polyester. According to exemplary embodiments, the cyclic ester comprises L-lactide, for example, at least 50 %, or at least 70 %, or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 %, or all, of the cyclic ester is L-lactide.

[0394] The obtained cyclic ester can be used in, for example, chemical or industrial process, as a reagent or starting material, for providing a variety of materials, products, or intermediates.

[0395] The obtained cyclic ester or mixture of cyclic esters can be used for forming a polyester (homopolymer, copolymer or block copolymer), for example, a recycled polyester which is made of the essentially the same cyclic ester(s) that formed it before its decomposition.

[0396] According to some of any of the embodiments described herein, the obtained cyclic ester is subjected to ring opening polymerization to thereby obtain a recycled polyester, and the process further comprises subjecting the cyclic ester to ring opening polymerization to thereby obtain the polyester.

[0397] The ROP can be performed using any of the respective catalysts known in the art (e.g., tin octanoate). In exemplary embodiments, the ROP is performed using a complex or a catalyst system as described herein in any of the respective embodiments. In exemplary embodiments, the ROP is performed using a complex or a catalyst system or a process as described in WO 2023 / 053128 and WO 2023 / 053127. In exemplary embodiments, the ROP is performed using a complex or a catalyst system or a process as described in WO 2017 / 137990. The methodology described herein in which polyester polymers are depolymerized back into their original monomeric cyclic ester building blocks through chemical means, enable full material circularity and the production of virgin-quality feedstock. The cyclic ester monomers are recovered in high purity and can be reused in polymerization or other chemical syntheses and / or processes or applications. The CRM process is particularly suitable for post-consumer and postindustrial polyester waste streams, including textiles, packaging, and biodegradable plastics. Applications of CRM include closed-loop recycling systems, reduction of fossil-based resource dependency, feedstock recovery for high-purity polymer manufacturing, and upcycling into specialty chemicals or biodegradable intermediates.

[0398] According to an aspect of some embodiments of the present invention there is provided a process of recycling a polyester, by decomposing it into its cyclic ester building blocks and subjecting the obtained building blocks to ROP to provide a recycled polyester, which can thereafter be subjected again to the CRM process, and so forth.

[0399] In some embodiments, recycling the polyester is effected by contacting the polyester or a composition or article-of-manufacturing comprising same, as described herein in any of the respective embodiments, with a catalyst system that forms an organometallic complex as described herein in any of the respective embodiments, under a condition that effects degradation of the polyester to the cyclic ester that composes it, as described herein in any of the respective embodiments, to thereby obtain the cyclic ester; subjecting the cyclic ester to a condition that effects ring opening polymerization, as described herein in any of the respective embodiments, thereby obtaining a recycled polyester.

[0400] The recycled polyester can be used to form articles-of-manufacturing and compositions that comprise a polyester, as described herein in any of the respective embodiments, or can be integrated within such articles or compositions.

[0401] The recycled polyester or a composition or article-of-manufacturing comprising same, or a part thereof, can then be subjected to a CRM process as described herein, by repeating the contacting with the catalyst system to thereby obtain again a cyclic ester. The cyclic ester can then be used to provide again a recycled polyester, and so forth.

[0402] The methodology described herein can be utilized for preparing a polyester that is capable of decomposing into the cyclic ester from which the polyester is formed, which is also referred to herein as a self-decomposing polyester, or as a polyester that can undergo CRM, or as a recyclable polyester.

[0403] According to an aspect of some embodiments of the present invention there is provided a process of preparing a self-decomposing polyester, which is effected by contacting the cyclic ester with a catalyst system that forms an organometallic complex as defined herein in any of the respective embodiments, to thereby obtain a polyester-containing material by ROP, for example, as described in 2023 / 053128 and WO 2023 / 053127. The obtained polyester comprises an amount of the organometallic complex that can then promote the CRM process when the polyester or a composition or article comprising same is subjected to a condition that effects decomposition or degradation of the polyester, as described herein.

[0404] According to some of these embodiments, the (recyclable) polyester prepared by the ROP can be integrated with or used to prepare a polyester-containing article-of-manufacturing or composition as described herein in any of the respective embodiments. According to some of any of these embodiments, the polyester prepared by the ROP or a composition or an article-of- manufacturing comprising same is maintained under conditions that maintain an activity of the organometallic complex. Such conditions include, for example, temperature below 150, or below 120, preferably below 100, °C, low humidity, and preferably low exposure to oxygen or air.

[0405] The obtained polyester or composition or article comprising same can then be subjected, during a time period of, for example, a few months to a few years, to decomposition by CRM, by subjecting it to a condition that effects degradation of the polyester, as described herein in any of the respective embodiments.

[0406] The time period and the extent of the degradation of the polyester can be manipulated, for example, by controlling the amount of the organometallic complex used to prepare the polyester. Higher amounts provide higher degradation extent and / or allow longer time periods before subjecting the polyester to the condition that effects degradation (e.g., heating, optionally along with an addition of a metal reagent and / or a hydroxy-containing compound, as described herein).

[0407] According to an aspect of some embodiments of the present invention there is provided a self-decomposing polyester (capable of undergoing self-CRM) that is capable of decomposing into the cyclic ester from which the polyester is formed, prepared by the process as described herein in any of the respective embodiments. Such a polyester is also regarded as a recyclable polyester

[0408] According to an aspect of some embodiments of the present invention there is provided an article-of-manufacturing or composition that comprises the self-decomposing (e.g., recyclable) polyester as described herein. Any of the exemplary articles and compositions as described herein are contemplated.

[0409] According to an aspect of some embodiments of the present invention there is provided a self-decomposing (e.g., recyclable) polyester that is capable of decomposing into the cyclic ester from which the polyester is formed. As used herein the term “about” refers to ± 10 % or ± 5 %.

[0410] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0411] The term “consisting of’ means “including and limited to”.

[0412] The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0413] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0414] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0415] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0416] As used herein the term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.

[0417] Herein throughout, the phrase “linking moiety” or “linking group” describes a group that connects two or more moieties or groups in a compound. A linking moiety is typically derived from a bi- or tri-functional compound, and can be regarded as a bi- or tri-radical moiety, which is connected to two or three other moieties, via two or three atoms thereof, respectively. Exemplary linking moieties include a hydrocarbon moiety or chain, optionally interrupted by one or more heteroatoms, as defined herein, and / or any of the chemical groups listed below, when defined as linking groups.

[0418] When a chemical group is referred to herein as “end group” it is to be interpreted as a substituent, which is connected to another group via one atom thereof.

[0419] The term "alkyl", as used herein, describes a saturated aliphatic hydrocarbon including straight chain and branched chain groups. In some embodiments, the alkyl group has 1 to 20 carbon atoms. Whenever a numerical range; e.g., " 1-20", is stated herein, it implies that the group, in this case the alkyl group, may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms, etc., up to and including 20 carbon atoms. In some embodiments, the alkyl is a lower alkyl having 1 to 4 carbon atoms. The alkyl group may be substituted or unsubstituted, as indicated herein.

[0420] The alkyl group can be an end group, as this phrase is defined hereinabove, wherein it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, which connects two or more moieties via at least two carbons in its chain. When the alkyl is a linking group, it is also referred to herein as “alkylene” or “alkylene chain”.

[0421] The term “alkaryl” describes an alkyl, as defined herein, which is substituted by one or more aryl or heteroaryl groups. An example of alkaryl is benzyl.

[0422] Herein throughout, the term “alkyl” encompasses “alkaryl” unless specifically indicated otherwise.

[0423] The term alkenyl, as used herein, describes an alkyl, as defined herein, which contains a carbon-to-carbon double bond.

[0424] The term alkynyl, as used herein, describes an alkyl, as defined herein, which contains carbon-to-carbon triple bond.

[0425] The term "cycloalkyl" or “alicyclic” describes an all-carbon monocyclic or fused ring (z.e., rings which share an adjacent pair of carbon atoms) group where one or more of the rings does not have a completely conjugated pi-electron system. The cycloalkyl group may be substituted or unsubstituted, as indicated herein.

[0426] The term "aryl" describes an all-carbon monocyclic or fused-ring polycyclic (z.e., rings which share adjacent pairs of carbon atoms) groups having a completely conjugated pi-electron system. The aryl group may be substituted or unsubstituted, as indicated herein.

[0427] The aryl group can be an end group, as this phrase is defined hereinabove, wherein it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, which connects two or more moieties via at least two carbons in its chain. When the alkyl is a linking group, it is also referred to herein as “arylene”, for example, phenylene. The term "alkoxy" describes both an -O-alkyl and an -O-cycloalkyl group, as defined herein.

[0428] The term "aryloxy" describes an -O-aryl, as defined herein.

[0429] Each of the alkyl, cycloalkyl and aryl groups, including alkylene and arylene groups, in the general formulas herein, may be substituted by one or more substituents, whereby each substituent group can independently be, for example, halogen, alkyl, alkoxy, cycloalkyl, alkoxy, nitro, amine, hydroxyl, thiol, thioalkoxy, thiohydroxy, carboxy, amide, aryl and aryloxy, depending on the substituted group and its position in the molecule. Additional substituents are also contemplated.

[0430] The term "halide", "halogen" or “halo” describes fluorine, chlorine, bromine or iodine.

[0431] The term “haloalkyl” describes an alkyl group as defined herein, further substituted by one or more halide(s).

[0432] The term “hydroxyl” or "hydroxy" describes a -OH group.

[0433] The term "thiohydroxy" or “thiol” describes a -SH group.

[0434] The term "thioalkoxy" describes both an -S-alkyl group, and a -S-cycloalkyl group, as defined herein.

[0435] The term "thioaryloxy" describes both an -S-aryl and a -S-heteroaryl group, as defined herein.

[0436] The term “amine” describes a -NR’R” group, with R’ and R” as described herein.

[0437] The term "heteroaryl" describes a monocyclic or fused ring (z.e., rings which share an adjacent pair of atoms) group having in the ring(s) one or more atoms, such as, for example, nitrogen, oxygen and sulfur and, in addition, having a completely conjugated pi-electron system. Examples, without limitation, of heteroaryl groups include pyrrole, furan, thiophene, imidazole, oxazole, thiazole, carbazole, pyrazole, pyridine, pyrimidine, quinoline, isoquinoline and purine.

[0438] The term "hetero alicyclic" or "heterocyclyl" describes a monocyclic or fused ring group having in the ring(s) one or more atoms such as nitrogen, oxygen and sulfur. The rings may also have one or more double bonds. However, the rings do not have a completely conjugated pi- electron system. Representative examples are piperidine, piperazine, tetrahydrofuran, tetrahydropyrane, morpholino and the like.

[0439] The term "carboxy" or "carboxylate" describes a -C(=O)-OR' group, where R' is hydrogen, alkyl, cycloalkyl, alkenyl, aryl, heteroaryl (bonded through a ring carbon) or heteroalicyclic (bonded through a ring carbon) as defined herein.

[0440] The term “carbonyl” describes a -C(=O)-R' group, where R' is as defined hereinabove.

[0441] The above-terms also encompass thio-derivatives thereof (thiocarboxy and thiocarbonyl).

[0442] The term “thiocarbonyl” describes a -C(=S)-R' group, where R' is as defined hereinabove. A thiocarboxy group describes a -C(=S)-OR group, where R is as defined herein.

[0443] A "sulfinyl" group describes an -S(=O)-R' group, where R' is as defined herein.

[0444] A "sulfonyl" group describes an -S(=O)2-R' group, where Rx is as defined herein.

[0445] A "carbamyl" group describes an -OC(=O)-NR'R" group, where R' is as defined herein and R" is as defined for R'.

[0446] A "nitro" group refers to a -NO2 group.

[0447] A "cyano" or "nitrile" group refers to a -C=N group.

[0448] Representative examples of nitrogen-containing heteroaryls include, but are not limited to thiadiazole, pyridine, pyrrole, oxazole, indole, purine and the like. Other moieties are also contemplated.

[0449] Representative examples of nitrogen-containing heteroalicyclic include, but are not limited to, morpholine, thiomorpholine, piperidine, piperazine, hexahydroazepine and tetrahydropyrane.

[0450] Other moieties are also contemplated.

[0451] The term “piperazine" refers group group, where R’ and R’ ’ are as defined hereinabove.

[0452] The term “piperidine” refers to a group or a group, with R’ as defined herein.

[0453] The term “pyrrolidine” refers to group or a group, with R’ as defined herein.

[0454] The term “pyridine” refers t group.

[0455] The term pyrrole refers group, with R’ as defined herein. The term “morpholine” refers to group, and encompasses also thiomorpholine.

[0456] The term “thiomorpholine” refers t group.

[0457] The term “hexahydro azepine” refers t group.

[0458] As used herein, the term “alkylene glycol” describes a -O-[(CR’R”)Z-O]y-R”’ end group or a -O-[(CR’R”)Z-O]y- linking group, with R’, R” and R’” being as defined herein, and with z being an integer of from 1 to 10, preferably, from 2 to 6, more preferably 2 or 3, and y being an integer of 1 or more. Preferably R’ and R” are both hydrogen. When z is 2 and y is 1, this group is ethylene glycol. When z is 3 and y is 1, this group is propylene glycol. When y is 2-4, the alkylene glycol is referred to herein as oligo(alkylene glycol).

[0459] When y is greater than 4, the alkylene glycol is referred to herein as poly(alkylene glycol). In some embodiments of the present invention, a poly(alkylene glycol) group or moiety can have from 10 to 200 repeating alkylene glycol units, such that z is 10 to 200, preferably 10-100, more preferably 10-50.

[0460] Herein, the phrases “Group IV” metal, “tetravalent valent” metal and “group 4” metal all describe a metal that has a valency of 4, that is, is capable of forming at least four covalent bonds with four monovalent atoms. A “tetravalent metal” encompasses also metals which feature higher valency. In some of any of the embodiments described herein, M is zirconium or hafnium, preferably zirconium. Other tetravalent metals are also contemplated.

[0461] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0462] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples. EXAMPLES

[0463] Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

[0464] MATERIALS AND EXPERIMENTAL METHODS

[0465] Reactions with air- and / or water- sensitive compounds were carried out using standard Schlenk or glovebox techniques under dry argon or nitrogen atmosphere.

[0466] Toluene was refluxed over Na under argon atmosphere and distilled.

[0467] Dichloromethane was refluxed over calcium hydride under argon atmosphere and distilled.

[0468] Pentane was washed with HNO3 / H2SO4, refluxed over Na / benzophenone / tetraglyme solution under argon atmosphere and distilled.

[0469] Commercial grade PLLA flakes (Mn 38,000 grams / mol; molecular weight distribution (PDI) = 1.21) employed in the depolymerization experiments were purchased from Natureworks Ingeo 4032D.

[0470] A drinking cup made of PLLA employed in the depolymerization experiments was obtained from NatureWorks (Mn 38,000 grams / mol; molecular weight distribution (PDI) = 1.19).

[0471] A bottle-sourced PET (polyethylene terephthalate) employed in the depolymerization experiments was obtained from Sidel

[0472] Purple PLLA from 3D printing filament was obtained from eSun (Mn 46,000 grams / mol; molecular weight distribution (PDI) = 1.28).

[0473] 2-bromo-4-(terZ-butyl)phenol was purchased from Combi-Blocks and used as received.

[0474] Sodium hydride 60 % dispersion in mineral oil, nBuLi (2.5M in hexane), zirconium (IV) isopropoxy isopropanol complex, chloromethyl methyl ether and anhydrous 2-propanol were purchased from Sigma-Aldrich and used as received.

[0475] TMEDA was purchased from Alfa Aesar.

[0476] Hydrochloric acid (32%) and formaldehyde 35% were purchased from Bio-Lab and used as received.

[0477] Ammonium acetate was purchased from Strem and was dried for 24 hours by lyophilization before use.

[0478] 1,4-benzenedimethanol was purchased from Acros Organics and used as received.

[0479] 1,3,5-benzenetrimethanol was purchased from Angene

[0480] Polyethylene glycol (PEG) 400 and PEG 1000 were obtained from Sigma Aldrich.

[0481] PEG 2000 was obtained from Thermo Scientific. Ethoxylated glycerol was obtained from Angene.

[0482] 2-bromo-4-(terZ-butyl)phenol, 9-bromoanthracene, bis(pinacolato)diborane, Pd(dppf)Ch, and NaB(0Ac)3H were purchased from Angene and used as received.

[0483] L-lactide and D-lactide was purchased from Musashino Chemical Laboratory, Ltd. and were purified by recrystallization from toluene followed by sublimation. rac-Lactide was prepared by mixing equal amounts of purified D-lactide and L-lactide, followed by crystallization from toluene and sublimation prior to use. meso-Lactide (about 85%) was purchased from NatureWorks and purified by repeated crystallizations from 2- propanol to >99% purity (GC) and sublimed prior to use.

[0484] Tin (II) 2-ethylhexanoate (tin octanoate) was purchased from Sigma-Aldrich and distilled twice under vacuum prior to use.

[0485] Medium-pressure liquid chromatography was performed using Teledyne Isco CombiFlash Nextgen 300+, with RediSep silica columns.

[0486] The NMR data were measured on a Bruker Avance-400 and Avance-500 spectrometers. CDCL was used as NMR solvent for the starting materials, building blocks, proligands and PLA, with theXH chemical shift of TMS at 5 = 0.00, and13C chemical shift of chloroform at 5 = 77.16. CeDr, was used as NMR solvent for the metal complexes, and lactide with chemical shifts of benzene at 5 = 7.16 (forXH NMR) and 5 = 128.06 (for13C NMR) as references.

[0487] Mass-spectrometric data were obtained on Waters XEVO-TQD MS spectrometer with the ESI ionization method (positive or negative).

[0488] APPI (Atmospheric Pressure Photo Ionization) was measured on SYNAPT QTof HDMI mass spectrometer (Waters Inc., USA) with Syagen 10.6 eV krypton discharge Lamp in positive mode. The sample was dissolved in toluene under dry nitrogen atmosphere and injected to the MS with a syringe pump under dry nitrogen flow. The de-solvation gas flow was 700 L / h at 450 °C. Repeller potential was 1.2 KV and sampling con was 40 V. The data was processed with Masslynx software.

[0489] PLA molecular weights and dispersity (£>; representing the molecular weight distribution Mw / Mn) were measured by gel permeation chromatography (GPC) using TSKgel GMHHR-M and TSKgel G 3000 HHR columns set on a Jasco instrument equipped with a refractive index detector. The molecular weights were determined relative to polystyrene standards using THF (HPLC grade) as the eluting solvent.

[0490] Polymerization of L-lactide (L-LA) or caprolactone (CPL) with Lig1,2Zr(O-zPr)(HO-zPr) or the pre-catalyst Lig7Mg-HMDS were performed according to the following general procedure: In a glovebox, a solution of 2-propanol (initiator) in dichloromethane (2 mL) was added to a solution of the metal complex in dichloromethane (2 mL). After a few minutes of stirring, the lactide or caprolactone was added and the mixture was stirred at room temperature. After the required time the reaction was quenched by exposure to air and the solvent was removed under vacuum. The resulting mixture was analyzed byXH NMR to determine the conversion, and the product was analyzed by GPC as described herein. Table A below summarizes the polymerizations data. The catalyst / initiator / monomer ratio represents the total initiator molecules in reaction. The calculated Mn was determined from (lactide / caprolactone Mw) x (monomer to ratio) x (conversion of monomer). The found Mn was determined by GPC using polystyrene standards with x0.58 (for PLA) and x0.56 (for polycaprolactone) correction parameter. Dispersity was determined by GPC, as described herein.

[0491] Table A EXAMPLE 1

[0492] FIG. 2A presents the chemical structures of exemplary amine tris(phenolate) ligands that were used to form exemplary zirconium complexes as described herein. Exemplary procedures for the preparation of utilization of these ligands - Lig2Hs and Lig5Hs and the zirconium complexes made therefrom, Lig2Zr(O-iPr)(HO-iPr), [Lig5Zr(O-tBu)]2 and [Lig5Zr(O-iPr)]2 are described in WO 2023 / 053128 and / or are according to respective procedures described in Hador et al., ACS Cat. 2022, 12, 4872-4879. Lig4Hs and its zirconium complex Lig4Zr(O-zPr) were synthesized according to a literature procedure (Chmura et al., Chem. Commun. 2008, 1293-1295). Lig6Hs was synthesized according to a literature procedure (Koi et al., Inorg. Chem. Commun. 2001, 4, 177-179). Lig7H and the bis(homoleptic) complex Lig62Zr were synthesized according to the procedure described in Davidson et al., Chem. Commun. 2003, 3, 1832-1833. The metal complex (pre-catalyst) Lig7Mg-HMDS, and the catalysts Lig7Mg-OiPr or Lig7Mg-OBn prepared therefrom were synthesized according to Rosen et al., Angew. Chem. Int. Ed. 2018, 57, 7191-7195.

[0493] Other ligands and respective complexes were synthesized as follows.

[0494] Ligands:

[0495] Synthesis of Lig'Hj:

[0496] Preparation of 5-(tert-butyl}-2',4',6'-trimethyl-[l,l '-biphenyl]-2-ol: The synthesis is based on the procedure employed for preparation of a related building block [Hador et al., ACS Cat. 2022, 12, 4872-4879]. In a pressure flask, sodium hydride (60 % dispersion in mineral oil, 1.3 gram, 32.5 mmol) was suspended in THF (40 mL) and the flask was cooled to 0 °C. 2-Bromo-4- (terZ-butyl)phenol (5.73 grams, 25 mmol) was slowly added and the flask was warmed to room temperature. After stirring for 10 minutes, mesitylmagnesium bromide IM solution in THF (36.0 mF, 36.0 mmol) was added followed by palladium (II) acetate 98 % (0.253 gram, 1.13 mmol) and the flask was heated to 70 °C. After stirring overnight, the flask was cooled to 0 °C and the reaction was quenched by adding aqueous HC1 solution (2M, 50 mL). The resulting mixture was filtered through celite, and the celite was extracted with ethyl acetate (3x50 mL). The phases were separated and the aqueous phase was extracted with ethyl acetate (3x50 mL). The combined organic phase was washed with brine, dried over sodium sulfate, filtered, and the solvent was removed under vacuum. The crude product was purified by column chromatography over silica gel eluted with 5 % ethyl acetate in hexane yielding the desired product with traces of impurities (95 % purity) as a pale-yellow solid (5.62 grams, 84 %).

[0497] ’ H NMR (CDC13, 400 MHz): δ = 7.29 (dd, 1H, J=2.5 Hz, J=8.5 Hz, ArH), 7.03 (d, 1H, J=2.5 Hz, ArH), 7.01 (s, 2H, MsH), 6.92 (d, 1H, J=8.5 Hz, ArH), 4.49 (s, 1H, ArOH), 2.35 (s, 3H, MSCH3), 2.03 (s, 6H, MsCH3), 1.31 (s, 9H, ArC(CH3)3).

[0498] Preparation of Liy1He A pressure flask was charged with 5-(tert-butyl)-2',4',6'-trimethyl- [l,l'-biphenyl]-2-ol (1.77 gram, 6.6 mmol), hexamethylenetetramine (0.076 gram, 0.54 mmol), 35 % aqueous solution of formaldehyde (0.75 mL , 9.5 mmol) and magnetic bar. The flask was sealed and heated to 130 °C for 48 hours to yield a yellow solid. The crude yellow solid was treated with methanol to obtain a mixture of white solid and yellow solution. Separation of the white solid from the yellow solution and methanol washes (3x30 mL) afforded Lig1H3as a white powder (0.662 gram, 35 %).

[0499] ’ H NMR (CDC13, 400 MHz): δ = 7.17 (d, 3H, J=2.5 Hz, ArH), 6.952 (d, 3H, J=2.7 Hz, ArH), 6.945 (s, 6H, MsH), 6.58 (br s, 3H, ArOH), 3.81 (s, 6H, ArCH2), 2.33 (s, 9H, MsCH3), 1.97 (s, 18H, MSCH3), 1.29 (s, 27H, ArC(CH3)3), ppm.

[0500] 13C NMR (CDC13, 100 MHz): δ = 150.3 (C), 142.5 (C), 137.5 (C), 137.3 (C), 134.0 (CH), 128.5 (CH), 126.9 (CH), 126.8 (CH+C), 122.0 (C), 55.1 (ArCH2), 34.2 (ArC(CH3)3), 31.8 (ArC(CH3)3), 21.2 (MsCH3), 20.5 (MsCH3), ppm.

[0501] MS (ESI): Calc, for C6oH7503N: 857.6, found: 858.7 (MH+), 856.7 (M-).

[0502] Elemental analysis: Calc. (%) for C6oH7503N: C, 83.97; H, 8.81; N, 1.63, found: C, 83.29; H, 9.02; N, 1.49.

[0503] Synthesis of Lig3H 3:

[0504] Preparation of 2-bromo-4-( tert-butyl -l -( methoxymethoxy)benzene: This compound was synthesized by a modified literature procedure [Ooi et al., J. Am. Chem. Soc. 2007, 129, 2410- 2411]. 2-Bromo-4-(terZ-butyl)phenol (2.5 grams, 10.9 mmol) was added to a suspension of NaH (0.52 gram; 60 % dispersion in mineral oil, 13.1 mmol) in THF (40 mL) under argon at 0 °C. After 1 hour of stirring at room temperature, chloromethyl methyl ether ( 1.65 mL, 21.8 mmol) was added dropwise to the solution at 0 °C. Stirring continued for 4.5 hours at room temperature. The reaction was quenched with water and then extracted with ethyl acetate (3x50 mL). The combined organic layers were washed with brine (1x50 mL). The solution was dried over Na2SO4, filtered, and the solvent was removed under vacuum. The residue was purified by medium-pressure column chromatography on silica gel (5 / 95 EtOAc / hexane as eluent) giving a clear oil in a yield of 88 %.

[0505] 1H NMR (400 MHz, CDC13): δ = 7.57 (d, 1H, 7=2.4 Hz, ArH), 7.28 (dd, 1H, 7=8.6, 2.4 Hz, ArH), 7.11 (d, 1H, 7=8.6 Hz, ArH), 5.24 (s, 2H, OCH2O), 3.54 (s, 3H, OCH3), 1.32 (s, 9H, C(CH3)3), ppm.

[0506] Preparation of 2-(anthracen-9-yl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane: 9- Bromoanthracene (10 grams, 38.8 mmol), bis(pinacolato)diborane (20 grams, 78.75 mmol) and potassium acetate (11.5 grams, 117.17 mmol) were dissolved in 1,4-dioxane (100 mL) under argon. Pd(dppf)Cl2(1.42 gram, 1.94 mmol) was added, and the red solution was heated to 90 °C for 24 hours. The brown solution was cooled to room temperature and diluted with dichloromethane. The mixture was filtered through celite and the solvent was removed under vacuum. The residue was purified by medium pressure column chromatography on silica gel (1 / 99 EtOAc / hexane as eluent) giving a white solid in a yield of 74 %.

[0507] 1H NMR (400 MHz, CDC13): δ = 8.49 (s, 1H, AntH), 8.57 (d, 2H, 7=6.9 Hz, AntH), 8.01 (d, 2H, 7=8.3, Ant / 7), 7.54-7.43 (m, 4H, Ant / 7), 1.60 (s, 12H, BPin / 7).13C NMR (100 MHz, CDCI3) 5 136.00 (2xAntC), 131.21 (3xAntC), 129.59 (AntCH), 128.88 (2xAntCH), 128.39 (2xAntCH), 125. 86 (2xAntCH), 124.95 (2xAntCH), 84.44 (2xBPinC(CH3)2), 25.24 (4xBPinC(CH3)2).

[0508] Preparation of 9-( 5-(tert-butyl)-2-(methoxymethoxy)phenyl}anthracene: 2-Bromo-4-(terZ- butyl)-l -(methoxy metho xy)benzene (4.28 grams, 15.68 mmol) and 2-(anthracen-9-yl)-4, 4,5,5- tetramethyl-l,3,2-dioxaborolane (7.156 grams, 23.4 mmol) and potassium carbonate (6.50 grams, 47.00 mmol) were dissolved in 1,4-dioxane / water solution (40 mL / 8 mL) under argon. Pd(dppf)Cl2(580 mg, 0.78 mmol) was added, and the red solution was heated to 100 °C for 12 hours. The brown solution was cooled to room temperature and the solvents were removed under vacuum. The mixture was diluted with dichloromethane, filtered through celite, dried over MgSCE and the solvent was removed under vacuum. The residue was purified by medium pressure column chromatography on silica gel (1 / 99 EtOAc / hexane as eluent) giving a white solid in a yield of 43 %.

[0509] 1H NMR (400 MHz, CDCI3): δ = 8.52 (s, 1H, AntH), 8.07 (d, 2H, 7=8.6 Hz, AntH), 7.69 (d, 2H, 7=8.9 Hz, AntH), 7.55 (dd, 1H, 7=9.1, 2.6 Hz, ArH), 7.54-7.46 (m, 2H, AntH), 7.40-7.33 (m, 3H, 2xAnt / 7 + ArH), 7.29 (d, 1H, 7=9.1 Hz, ArH), 4.89 (s, 2H, OC772O), 3.04 (s, 3H, OCft), 1.37 (s, 9H, C(C773)3), ppm.

[0510] 13C NMR (100 MHz, CDCI3): δ = 153.20 (ArC), 144.82 (ArC), 134.39 (ArC), 131.45 (2xAntC), 130.46 (2xAntC), 130.07 (ArCH), 128.36 (2xAntCH), 127.80 (AntC), 126.97 (2xAntCH), 126.43 (ArCH), 125.89 (ArCH), 125.20 (2xAntCH), 125.04 (2xAntCH), 114.86 (AntCH), 94.43 (OCH2O), 55.77 (OCH3), 34.35 (C(CH3)3), 31.52 (C(CH3)3), ppm.

[0511] MS: (ES+) calc, for C26H26O2370.49 found 393.4 (+Na+).

[0512] Preparation of 3-(anthracene-9-yl)-5-(tert-butyl)-2-(methoxymethoxy)benzaldehyde: This compound was synthesized by following a literature procedure employed for related materials [Hador et al., ACS Cat. 2022, 12, 4872-4879]. 9-(5-(tert-butyl)-2-

[0513] (methoxymethoxy)phenyl)anthracene_(2.44 grams, 6.58 mmol) was dissolved in dry diethyl ether (40 mL). Under argon, TMEDA (2 mL, 13.2 mmol) was added to the solution, followed by addition of n-BuLi (4.5 mL; 2.5M in hexane, 11 mmol) at 0 °C. The yellow suspension was stirred at 0 °C for 3 hours. Anhydrous DMF (1.1 mL, 13.2 mmol) was added to the solution and the stirring continued for 1 hour at 0 °C. The reaction was quenched with saturated ammonium chloride solution (40 mL) and then extracted with diethyl ether (2x40 mL). The combined organic layers were washed with brine (1x50 mL). The solution was dried over MgSCU, filtered and the solvent was removed under vacuum. The residue was purified by medium pressure column chromatography on silica gel (2:98 EtOAc / hexane as eluent) giving a pale-yellow solid in a yield of 82 %.

[0514] ’ H NMR (400 MHz, CDC13): δ = 10.55 (s, 1H, CHO), 8.57 (s, 1H, AntH), 8.11-8.07 (m, 3H, ArH + 2xAntH), 7.68-7.65 (m, 3H, ArH + 2xAntH), 7.53-7.49 (m, 2H, AntH), 7.46-7.42 (m, 2H, 2xAntH), 4.34 (s, 2H, OCH2O), 2.76 (s, 3H, OCH3), 1.39 (s, 9H, C(CH3)3), ppm.

[0515] 13C NMR (100 MHz, CDC13): δ = 191.07 (CHO), 156.80 (ArC), 147.84 (ArC), 137.12 (ArCH), 132.39 (ArC), 132.13 (ArC), 131.35 (2xAntC), 130.29 (2xAntC), 129.59 (AntC), 128.58 (2xAntCH), 127.51 (ArCH), 126.24 (2xAntCH), 126.16 (2xAntCH), 125.33 (2xAntCH), 124.93 (AntCH), 99.79 (OCH2O), 57.00 (OCH3), 34.80 (C(CH3)3), 31.31 (C(CH3)3), ppm.

[0516] MS: (ES+) calc, for C27H26O3398.50 found 421.5 (+Na+).

[0517] Preparation of Tris(3-(anthracene-9-yl}-5-(tert-butyl}-2-(methoxymethoxy}benzyl} amine: This compound was synthesized by following a literature procedure employed for related ligands [Hador et al., ACS Cat. 2022, 12, 4872-4879]. Ammonium acetate (111 mg, 1.44 mmol) was added to a solution of 3-(anthracene-9-yl)-5-(tert-butyl)-2-(methoxymethoxy)benzaldehyde (1.72 gram, 4.32 mmol) in dry THF (20 mL). After a few minutes, NaB(OAc)3H (1.37 gram, 6.47 mmol) was added. The mixture was stirred at room temperature for 12 hours, followed by addition of a second portion of NaB(OAc)3H (1.37 gram, 6.47 mmol). After 6 hours, another portion was added, and the mixture was stirred for additional 72 hours. The reaction was quenched with NaOH 4M, and extracted with ethyl acetate (2x30 mL). The combined organic layers were washed with brine (1x50 mL). The solution was dried over MgSCU, filtered, and the solvent was removed under vacuum. The residue was purified by medium pressure column chromatography on silica gel (10:90 EtOAc / hexane as eluent) giving a white solid in a yield of 57 %.

[0518] ’ H NMR (400 MHz, CDC13): δ = 8.52 (s, 3H, AntH), 8.31 (distorted d, 3H, ArH), 8.05 (d, 6H, 7=8.9 Hz, AntH), 7.78 (d, 6H, 7=8.2 Hz, AntH), 7.49-7.45 (m, 6H, AntH), 7.42-7.37 (m, 6H, AntH), 7.31 (distorted d, 3H, ArH), 4.27 (s, 6H, OCH2O), 4.17 (s, 6H, NCH2Ar), 2.46 (s, 9H, OCH3), 1.44 (s, 27H, C(CH3)3), ppm.

[0519] 13C NMR (100 MHz, CDC13): δ = 151.90 (3xArC), 147.23 (3xArC), 134.40 (3xArC), 133.11 (3xAntC), 131.38 (6xAntC), 130.90 (3xArC), 130.47 (6xAntC), 128.67 (3xArCH), 128.31 (6xAntCH), 127.00 (6xAntCH), 126.67 (3xArCH), 125.92 (3 x AntCH), 125.64 (6x AntCH), 125.14 (6xAntCH), 98.56 (OCH2O), 56.30 (OCH3), 53.44 (NCH2Ar), 34.75 (C(CH3)3), 31.75

[0520] (C(CH3)3), ppm.

[0521] MS: (ES+): calc, for C8IH8INO61164.54 found 1165.2 (+H+).

[0522] Preparation of Liz' 'Hi: Tris(3-(anthracen-9-yl)-5-(tert-butyl)-2-(methoxymethoxy) benzyl)amine (0.95 gram, 0.82 mmol) was dissolved in a 2: 1 mixture of THF (8 mL) and methanol (4 mL). Hydrochloric acid (32 %) (6 mL) was added. The solution was stirred overnight at room temperature followed by addition of another portion of HC1 (10 mL). After another 24 hours of stirring, the reaction was quenched with 4M NaOH solution. The residual aqueous phase was extracted with ethyl acetate (3X 30 mL). The combined organic layer was washed with brine (1x30 mL). The solution was dried over MgSCU, filtered, and the solvent was removed under vacuum. The residue was purified by medium pressure column chromatography on silica gel (4 / 96 EtOAc / hexane as eluent) giving a white solid in a yield of 53 %.

[0523] ’ H NMR (400 MHz, CDC13): δ = 8.41 (s, 3H, AntH), 7.93 (d, 6H, 7=8.4 Hz AntH), 7.51 (d, 6H, 7=8.9 Hz, AntH), 7.39 (d, 3H, 7=2.1 Hz, ArH), 7.22-7.19 (m, 6H, AntH), 7.16 (d, 3H, 7=2.1 Hz, ArH), 6.81-6.77 (m, 6H, AntH), 4.01 (s, 6H, NCH2Ar), 1.26 (s, 27H, C(CH3)3), ppm.

[0524] 13C NMR (100 MHz, CDC13): δ = 151.63 (3xArC), 142.28 (3xArC), 132.08 (3xArC), 131.38 (6xAntC), 130.53 (6xAntC), 128.84 (3xArCH), 128.12 (6xAntCH), 127.88 (3xArCH), 126.88 (3xAntCH), 126.56 (6xAntCH), 125.55 (6xAntCH), 125.08 (6xAntCH), 124.30 (3xAntC), 122.90 (3xArC), 55.86 (NCH2Ar), 34.13 (C(CH3)3), 31.63 (C(CH3)3), ppm.

[0525] MS: (ES+) calc, for C75H69NO31032.38 found 1033.2 (+H+).

[0526] Metal Complexes:

[0527] Synthesis ofLig1Zr( O-iPr)(HO-iPr):

[0528] In a glove box, zirconium (IV) isopropoxy isopropanol (0.045 gram, 0.12 mmol) was dissolved in toluene (1 mL). LigxH3(0.1 gram, 0.12 mmol) was dissolved in toluene (1 mL) and was slowly added to the solution of the zirconium complex. After 2 hours of stirring, the solvent was removed under vacuum and the residue was recrystallized from cold pentane (3x1 mL) and dried under vacuum to yield the desired complex as a white powder (0.087 gram, 70 %).

[0529] 1H NMR (C6D6, 400 MHz): 8 = 7.20 (d, 3H, 7=2.6 Hz„ ArH), 7.10 (d, 3H, 7=2.5 Hz, ArH), 6.90 (s, 6H, MsH), 3.76-3.27 (broad peak, 8H, ZrOCH(CH3)2+(CH3)2CHOH+ArCH2), 2.21 (s, 18H, MSCH3), 2.18 (s, 9H, MsCH3), 1.33 (s, 27H, ArC(CH3)3), 0.71 (d, 12H, 7=6.2 Hz, ZrOCH(CH3)2+(CH3)2CHOH), ppm.

[0530] 13C NMR (C6D6, 100 MHz): 8 = 156.1 (C), 140.8 (C), 136.8 (C), 136.6 (C), 136.0 (C), 128.6 (CH), 128.4 (CH), 125.9 (CH), 124.4 (C), 70.9-69.5 (broad absorption), 60.5, (ArCH2), 34.2 (ArCCH3)3), 32.0 (ArCCH3)3), 25.0-24.6 (broad absorption), 21.1 (MsCH3), ppm. MS (APPI): Calc, for C63H79O4NZr(zPrOH): 1063.6, found: 1003.5 [M-(zPrOH)-+],

[0531] Elemental analysis: Calc. (%) for CeeHsvOsNZr: C, 74.39; H, 8.23; N, 1.31, found: C, 72.94; H, 8.60; N, 1.17.

[0532] The crystallographic structure of Lig1Zr(O-iPr)(HO-iPr) is presented in FIGs. 2B-C.

[0533] Crystal data for complex Lig^rfO-iPr^HO-iPr): CeeHsvOsNZr; 47=1089.14; monoclinic; space group P 1 21 / c 1; a=12.1061(2) A, ^=23.2755(3) A, c=24.3836(3) A, tr=y=90°, ^=102.8890(10)°, 7=6697.59(16) A3; 7=110(2) K; Z=4; Dc=1.080 g cm’3; g(Mo Ka)=1.680 mm’1; Ri=0.0361 and w7?2=0.0922 for 10858 reflections with / >2c (I); Ri=0.0408 and wT?2=0.0955 for all 12188 unique reflections.

[0534] Synthesis of Lig3Zr(O-iPr)(HO-iPr):

[0535] In a glove box, Lig3H3 (50 mg, 0.048 mmol) was suspended in toluene (1 mL). Zirconium (IV) isopropoxy isopropanol (18.8 mg, 0.048 mmol) was dissolved in toluene (1 mL) and the suspension of Lig3H3 was slowly added to the solution of the zirconium complex. The obtained pale-yellow solution was stirred at room temperature. After 2 hours, the solvent was removed under vacuum and the residue was washed with pentane (3x1 mL) and dried under vacuum to yield the desired complex as a yellow solid (0.045 gram, 80 %).

[0536] 1H NMR (400 MHz, C6D6): δ = 8.06 (s, 3H, AntH), 7.83 (d, 6H, 7=8.8 Hz, AntH), 7.70 (d, 6H, 7=8.2 Hz, Ant / 7), 7.44 (d, 3H, 7=2.5 Hz, ArH), 7.37 (d, 3H, 7=2.5 Hz, ArH), 7.11-7.06 (broad peak, 6H, Antff), 7.04- 7.03 (broad peak, 6H, Antff), 4.88-2.80 (broad peak, 8H, ZrOC77(CH3)2+(CH3)2C77OH+ArC7f2) 1.37 (s, 27H, QCfth), -0.04 (broad peak, 6H, ZrOCH(C773)2), -0.92 (broad peak, 6H, (CfthCHOH), ppm.

[0537] 13C NMR (100 MHz, C6D6): δ = 157.26 (3xArC), 140.58 (3xArC), 135.19 (3xArC), 131.69 (6xAntC), 130.57 (6xAntC), 130.08 (3xArCH), 128.40 (6xAntCH), 127.92 (6xAntCH), 126.77 (3xArCH), 126.10 (6xAntCH), 125.95 (3xAntC), 125.43 (3xAntCH), 124.68 (6xAntCH), 124.53 (3xArC), 60.70 (NCTfcAr), 33.97 (ArC(CH3)3), 31.64 (ArC(CH3)3), ppm.

[0538] EXAMPLE 2

[0539] Preliminary experiments revealed that warming commercial PLLA to 180 °C in the presence of the amine tris(phenolate) zirconium catalysts as described herein led to its decomposition and to substantial formation of L-lactide. Several control experiments were conducted in order to verify that these complexes are responsible for the decomposition of the PL A to monomer: (1) attempting to depolymerize the same commercial PLLA with no added catalyst gave no lactide; (2) attempting to employ simple compounds of zirconium like commercial zirconium isopropoxide (Zr(OiPr)4(HOiPr)) gave essentially no lactide; (3) other simple zirconium compounds like zirconium lactate gave no lactide; and (4) employing an amine tris(phenolate) ligand (Lig1Hs) without a metal resulted in no depolymerization. These experiments therefore demonstrated that the catalyst is required for decomposition of commercial PLA to the lactide monomer. Thus, the complexes described herein, featuring a specifically-designed amine tris(phenolate) ligand were found to be superior to simpler zirconium complexes such as described in the art for this transformation, whereby the ligand without zirconium was not able to promote this depolymerization.

[0540] Comparative depolymerization experiments varying the employed complexes and the depolymerization conditions were conducted. In all experiments, the experimental setup included a glass vacuum sublimator, such as shown in FIG. 3.

[0541] The general depolymerization procedure included mixing commercial PLLA flakes (7.5 mmol of lactide repeat units) with a catalyst (2.5 pmol) - 1:3000 molar ratio of catalyst to lactide equivalents (which can also be expressed as 1:6000 catalyst to lactic acid equivalents) - in 5 mL of dichloromethane for the required time for full dissolution in a glovebox under nitrogen, in the bottom part of the sublimator. Then, the solvent was removed under vacuum, and the sublimator was assembled under nitrogen and sealed. The sublimator, charged with the PLA and the catalyst, was connected to a vacuum line and its bottom part was immersed in an oil bath which was warmed to 180 °C for 4 hours while the cold spot in the sublimator was cooled to 0 °C. The decomposition of the polymer to the lactide monomer occurred in the presence of the catalyst at 180 °C, and the formed lactide sublimed under this vacuum and was collected at the cold spot. Following the elapsed time, the sublimator was removed from the oil bath, and allowed to reach room temperature. The sublimator was then disassembled, and the lactide collected at the cold spot was removed and weighed, and analyzed by NMR in CeDe to determine its chemical purity and the ratio of the obtained lactide stereoisomers.

[0542] It was found that the formed lactide is of very high chemical and stereochemical purity, exceeding 97 % of L-lactide. Without being bound by any particular theory, it has been assumed that the presence of 2-3% of meso-lactide in the L-lactide originates from the stereochemical impurity of the commercial PLLA employed and not from epimerization side-reaction during the depolymerization process. A support to the above was demonstrated when a highly-isotactic PLLA, prepared in-house from pure L-lactide, depolymerized to L-lactide of > 99 % L-lactide.

[0543] The material that did not undergo sublimation was also analyzed by NMR and was found to consist of essentially unreacted PLLA.

[0544] Table 1 below presents the data obtained for depolymerization of commercial PLLA flakes at 180 °C. Table 1 volatiles.

[0545] Table 1 shows that the amine tris(phenolate) zirconium complexes that include an aromatic ortho-mesityl substituent exhibited the most promising results. The complex Lig2Zr(O-zPr)(HO- z’Pr) that includes a para-methyl group led to the highest conversion to lactide. The complex Lig4Zr(O-zPr) which includes bulky tert-butyl ortho and para substituents gave essentially no lactide. The dinuclear complexes [Lig5Zr(O-tBu)]2 and [Lig5Zr(O-zPr)]2 which bear ort / zo-phenyl substituents, and the bis(homoleptic) Lig62Zr complex were less efficient. Notably, tin octanoate, previously described for lactide polymerization, and for CRM of PLA, was considerably less efficient than the complexes described herein in PLA depolymerization. These results demonstrate that insightfully designed metal complexes of amine tris(phenolate) ligands should enable the efficient chemical recycling of PLA to monomer. It is also demonstrated that simple zirconium complexes - zirconium isopropoxide and zirconium lactate are not suitable catalysts for the CRM of PLA.

[0546] The effect of exposing the polymer and catalyst mixture to air before performing the depolymerization was also tested, based on the hypothesis that the humidity in the air may lead to exchange of the labile alkoxo group bound to the zirconium in the catalysts with a hydroxo group which may facilitate the depolymerization catalysis. Thus, the mixture of commercial PLLA and catalyst was dissolved in dichloromethane under nitrogen, but instead of removing the solvent in the glovebox, this was done under air, while assembling the sublimator in air and then conducting the depolymerization reactions.

[0547] These results are summarized in Table 2 below. As can be seen, exposing the mixture to air for several minutes was indeed beneficial, and higher yields of lactide were obtained. Notably, the purity of the obtained lactide remained very high. The complex Lig2Zr(O-zPr)(HO-zPr) exhibited impressive 93 and 97 % formations of lactide from PLLA. The simple zirconium isopropoxide compound Zr(O-zPr)4(HO-zPr) and the ligand with no zirconium Lig1Hs did not lead to any formation of lactide. Exposing complex Lig4Zr(O-zPr) which includes bulky tert-butyl ortho and para substituents to air did not yield any lactide either.

[0548] Table 2

[0549] EXAMPLE 3 The depolymerization of other forms of PLLA with the catalyst Lig2Zr(O-zPr)(HO-zPr) was tested.

[0550] Depolymerization of a drinking cup made of PLLA led to high yield of lactide under the same conditions. A depolymerization attempt of a mixture of cup-sourced PLA and bottle-sourced PET led to formation of a pure lactide, while the PET stayed intact, demonstrating that selective decomposition of PLA from non-sorted plastics may be attained.

[0551] FIG. 3 is a photograph of the sublimators used in these depolymerization runs; the right item is a sublimator after depolymerization of a PLA-consisting cup and the left item is a sublimator after depolymerization of a mixture of PLA-consisting cup and a PET -bottle. As can be seen, in both sublimators, the bottom part of the outer flask shows traces of unreacted polymer, and the inner tube is coated with white sublimed lactide. The blue color covering the white lactide in the sublimator shown in the left side is a dye originating from the PET bottle.

[0552] Depolymerization of various PLLA polymers made with the catalyst Lig7Mg-OiPr (prepared from Lig7Mg-HMDS in the presence of isopropanol) (see, Table A), of a mixture of commercial PLLA flakes and a poly(epsilon-caprolactone) (PCL) made with the catalyst Lig7Mg- OiPr (Mn= 47,600) (see, Table A), and of purple PLLA from 3D printing filament, were tested, and led to selective decomposition of PLA only, without affecting the PCL when present.

[0553] Table 3 below summarizes the data obtained for the CRM of the different types of tested polymers at 180 °C, while exposing the sublimator to air before performing the catalysis.

[0554] Table 3

[0555] Overall, the data presented herein show that metal complexes of amine tris(phenolate) ligands are highly efficient catalysts for the depolymerization of PLA, employed either in a pure form or in a non-sorted form, directly to lactide, demonstrating an efficient CRM of PLA for turning the PLA economy to circular.

[0556] EXAMPLE 4

[0557] Higher efficiencies of the depolymerization of PLA using the metal complexes of the amine tris(phenolate) ligands as described herein are achieved by addition of specific additives, and modification of the experimental setups.

[0558] Table 4 below presents the depolymerizations of commercial flakes of PLLA mixed with different alcohols at 180 °C with 1:20:3000 ratio of [Cat. / alcohol / LA units in the PLLA] (sublimator was sealed outside the glovebox).

[0559] Table 4 As can be seen, adding PEG 400 led to an increase in the yield of the obtained L-lactide obtained after 4 hours at 180 °C, with complexes made of Lig1and Lig2.

[0560] The decomposition results outlined in Table 4 reveal that addition of a polyalcohol is beneficial for the CRM process. Poly(ethylene-glycol)s (PEGs) result in superior performance, while shorter PEGs provide the most superior effect, which presumably, and without being bound to this particular theory, is attributed to the relative high proportion of -OH end groups relative to the molecular weight of the polymer.

[0561] EXAMPLE 5

[0562] In a different set of experiments, depolymerization of PLLAs made with Lig1Zr(O- iPr)(HO-iPr) or Lig2Zr(O-iPr)(HO-iPr), shown in Table A, upon exposure to air at 180 °C for 2 hours, without addition of catalyst, was tested. The data is presented in Table 5 below and show that depolymerization occurs under these conditions, also following 6 months from the polymer preparation. These data show that PLLAs made in the presence of catalysts as described herein can undergo self-CRM.

[0563] Table 5

[0564] * Depolymerization conversion

[0565] Further, the addition of Zr(O-zPr)4(HO-zPr) and Lig2Hs separately to a depolymerization mixture of commercial flakes of PLLA was tested at a 1: 3000 Cat. / LA units in the PLLA ratio, at 180 °C for 4 hours (sublimator was sealed outside the glovebox). Conversion was 81 % and lactide composition was 97 % L-LA and 3 % meso-LA. These data indicate that PLLAs can be decomposed by simply adding the metal precursor / reagent used for preparing the metal complexes, for example, Zr(O-zPr)4(HO-zPr), without preparing the catalyst ex-situ in advance.

[0566] These data further demonstrate that such a metal reagent can be added to PLLAs made in the presence of catalysts as described herein, for re-activating residual metal complexes in the polyester, or residual ligands, to thereby effect CRM.

[0567] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0568] It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A process of obtaining a cyclic ester that forms a polyester by ring opening polymerization thereof, from a composition that comprises said polyester, the process comprising contacting the composition with a catalyst system that forms an organometallic complex represented by Formula A:[(L)m(M)(X)z(X’)q]nFormula A wherein:M is a transition metal; n is an integer, representing the nuclearity of the complex, and can be, for example, 1, 2, 3, 4 or higher; m is a positive integer, for example, 1 or 2; z and q are each independently 0 or 1, wherein, preferably, z equals to or is higher than q;X is a monoanionic ligand which, when present, forms a covalent or coordinative bond with said metal;X’ is a neutral ligand, such as an alcohol which, when present, forms a coordinative bond with said metal; andL is a ligand derived from a ligand precursor represented by Formula IV :Formula IV wherein:W, Y and Z are each independently an arylene or a heteroarylene, at least one of W, Y and Z being a substituted arylene or a substituted heteroarylene, said at least one substituted arylene or heteroarylene comprising at least one aliphatic, alicyclic or aromatic substituent; andB l, B2 and B3 are each independently a bridging moiety linking between the respective aryl or heteroaryl and the nitrogen atom, or is absent,and wherein: at least one, and preferably each, of the -OH groups in said ligand precursor forms an M— O- bond with said metal, wherein the dashed line independently represents a covalent or coordinative bond; and said N is optionally attached to said M via a covalent or coordinative bond, and can be protonated or non-protonated, the process further comprising subjecting a reaction mixture comprising said composition and said organometallic complex to a condition that effects degradation of the polyester, to thereby obtain the cyclic ester.

2. The process of claim 1, wherein M is a Group IV metal.

3. The process of claim 1 or 2, wherein M is zirconium.

4. The process of any one of claims 1 to 3, wherein X is selected from alkyl, alkaryl, cycloalkyl, aryl, amide, alkoxy, thioalkoxy, aryloxy, thioaryloxy, halo and amine.

5. The process of any one of claims 1 to 4, wherein X’ is a neutral ligand selected from alkyl alcohol, aryl alcohol, aralkyl alcohol, and amine.

6. The process of any one of claims 1 to 5, wherein z and q are each 1, and X and X’ form together a monoanionic bidentate ligand.

7. The process of any one of claims 1 to 6, wherein each of said bridging moieties B l, B2 and B3 is independently a hydrocarbon of 1 to 6, or from 1 to 4, or from 1 to 2, carbon atoms in length.

8. The process of claim 7, wherein B 1 is represented by the Formula:-(CRaRb)-(CRcRd)ml- wherein: ml is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;Ra, Rb, Rc and Rd are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ra and Rb and / or Rc and Rd, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rc and Rd in each (CRcRd) unit can be the same or different, and one or both Rc and Rd in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rc and Rd of an adjacent unit.

9. The process of claim 7 or 8, wherein B2 is represented by the Formula:-(CReRf)-(CRgRh)m2- wherein: m2 is 0 or is a positive integer of from 1 to 5, or from 1 to 3, or from 1 to 2;Re, Rf, Rg and Rh are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Re and Rf and / or Rg and Rh, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rg and Rh in each (CRgRh) unit can be the same or different, and one or both Rg and Rh in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rg and Rh of an adjacent unit.

10. The process of any one of claims 7 to 9, wherein B3 is represented by the Formula:-(CRiRj)-(CRkRm)m3- wherein: m3 is 0 or is a positive an integer of from 1 to 5, or from 1 to 3, or from 1 to 2;Ri, Rj, Rk and Rm are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, or, alternatively, Ri and Rj and / or Rk and Rm, if present, form together a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring, wherein when m is other than 1, Rk and Rm in each (CRkRm) unit can be the same or different, and one or both Rk and Rm in one unitcan form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rk and Rm of an adjacent unit.

11. The process of any one of claims 1 to 10, wherein each of Y, Z and W is independently an arylene.

12. The process of claim 11, wherein said ligand precursor is represented by FormulaV:wherein:Bi, B2 and B 3 are as defined in any one of claims 1-11; andR1-R12 are each independently selected from hydrogen, alkyl, cycloalkyl, heteroalicyclic, aryl, heteroaryl, halo, alkoxy, and amino, or alternatively, two of R1-R4, and / or two of Rs-Rs, and / or two of R9-R12 independently form together a cyclic ring (fused to the phenolate ring), wherein at least one of R1-R12 is alkyl, cycloalkyl, aryl or heteroaryl, each independently being substituted or unsubstituted.

13. The process of claim 12, wherein said ligand precursor is represented by FormulaVI:Formula VI whereinRa, Rb, Re, Rf, Ri and Rj are each as defined in any one of claims 7 to 9.

14. The process of claim 12 or 13, wherein at least one, or each, of Ri, Rs and R9 is a substituted or unsubstituted aryl or heteroaryl.

15. The process of claim 12 or 13, wherein at least one, or each, of Ri, Rs and R9 is a substituted or unsubstituted alkyl, preferably a lower, non-bulky, alkyl.

16. The process of claim 14 or 15, wherein at least one of R2-R4, Re-Rs and R10-R12 is an alkyl, preferably a lower alkyl.

17. The process of claim 16, wherein said lower alkyl is a non-bulky lower alkyl.

18. The process of any one of claims 14, 16 or 17, wherein m is 1.

19. The process of claim 18, wherein M is a tetravalent group 4 metal, and wherein preferably, z and q are each 1.

20. The process of claim 19, wherein said complex is represented by Formula II or Formula III:Formula III wherein: n is said integer representing the nuclearity of the complex, as defined herein; and the dashed line represents a covalent or a coordinative bond representing a bond between a donor atom and said metal.

21. The process of any one of claims 1 to 17, wherein m is 2.

22. The process of claim 21, wherein M is a tetravalent group 4 metal, and wherein preferably, z and q are each 0.

23. The process of claim 22, wherein the complex is represented by Formula X or Formula XI:Formula XI wherein: the dashed line represents a covalent or a coordinative bond representing a bond between a donor atom and a metal; andBi, B2, B3 R1-R12, Ra, Rb, Re, Rf, Ri and Rj are each as defined herein in any one of claims 1 and 4 to 11, and can be the same or different in each ligand.

24. The process of any one of claims 1 to 23, wherein said catalyst system further comprises a hydroxy -containing material.

25. The process of claim 24, wherein said hydroxy-containing material is non-volatile.

26. The process of claim 24 or 25, wherein said hydroxy-containing material is Rk(OH)p, wherein p is an integer of from 1 to 6, and Rk is alkyl, cycloalkyl, alkaryl or aryl, or is a polymeric moiety.

27. The process of claim 26, wherein said polymeric moiety is or comprises a poly (alkylene glycol).

28. The process of claim 27, wherein a molecular weight Mn of said poly(alkylene glycol) is lower than 2,000, or lower than 1,000, or lower than 600 grams / mol.

29. The process of any one of claims 24 to 28, wherein a mol ratio of the hydroxycontaining material to the metal complex is in a range of from 1: 1 to 100: 1 or from 1: 1 to 50: 1, or from 10: 1 to 50: 1, or from 10: 1 to 30: 1.

30. The process of any one of claims 1 to 29, wherein at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 % of the obtained cyclic ester features substantially the same stereoconfiguration as the backbone units of the polyester.

31. The process of any one of claims 1 to 30, wherein said cyclic ester is or comprises a lactide, and said polyester is or comprises a poly(lactic acid) (PLA).

32. The process of claim 31, wherein said lactide is selected from homochiral lactide, racemic lactide and meso-lactide and any combination thereof, and wherein at least 50 %, or at least 60 %, or at least 70 % or at least 80 %, or at least 90 %, or at least 95 %, or at least 97 % of the lactide features the same stereoconfiguration as the backbone units of the polyester.

33. The process of any one of claims 1 to 32, wherein said organometallic complex is formed in situ such that said contacting is with said ligand precursor, and with a metal reagent M(X)z(Xi)w(X’)q, wherein:M is said transition metal,w is 0 or is an integer which together with z provides the valence number of said metal; z and 1 are each independently 0 or 1 ;X and X’ are each as defined herein; andXi is a monoanionic ligand, which can be the same or different from X, wherein when w is higher than 1, each Xi can be the same or different.

34. The process of any one of claims 1 to 33, wherein said condition for effecting said degradation comprises heating said mixture.

35. The process of claim 34, wherein said heating is at a temperature at which said polyester is in a molten state.

36. The process of any one of claims 1 to 35, further comprising separating said cyclic ester from the composition.

37. The process of claim 36, wherein said separating is by sublimating the cyclic ester and collecting it as a solid product.

38. The process of claim 36, wherein said separating is by distillation.

39. The process of any one of claims 1 to 38, wherein said composition comprises polymeric materials other than said polyester, and wherein at least 90 %, or at least 95 %, or at least 98 %, of a product obtained by the process consists of said cyclic ester.

40. The process of any one of claims 1 to 39, wherein said composition is exposed to aerobic environment prior to subjecting to said condition.

41. The process of any one of claims 1 to 40, wherein the composition that comprises the polyester further comprises said organometallic complex, and the process comprises subjecting the composition to said condition that effects degradation of the polyester.

42. The process of claim 41, wherein subjecting to said condition is performed during a time period that ranges from 1 day to 720, or from 1 to 365, or from 1 to 200, days, after the polyester that further comprises said organometallic complex is prepared.

43. The process of any one of claims 1 to 40, further comprising subjecting the cyclic ester to ring opening polymerization to thereby obtain the polyester.

44. A cyclic ester obtained by the process of any one of claims 1 to 40.

45. A process of preparing a polyester that is capable of decomposing into the cyclic ester from which the polyester is formed, the process comprising contacting the cyclic ester with a catalyst system that comprises an organometallic complex as defined in any one of claims 1 to 29, to thereby obtain a polyester-containing material, and maintaining the polyester or a composition or an article-of-manufacturing comprising same under conditions that maintain an activity of the organometallic complex, wherein said decomposing comprises subjecting the polyester or a composition or article- of-manufacturing comprising same to a condition that effects degradation of the polyester.

46. The process of claim 45, wherein said decomposing further comprises contacting the polyester or a composition or article-of-manufacturing comprising same with a metal reagent and / or a hydroxy -containing material that re-activates said organometallic complex.

47. A self-decomposing polyester that is capable of decomposing into the cyclic ester from which the polyester is formed, prepared by the process of any one of claims 45 to 46.

48. An article-of-manufacturing comprising the self-decomposing polyester of claim 47.

49. A self-decomposing polyester that is capable of decomposing into the cyclic ester from which the polyester is formed.

50. A process of recycling a polyester, the process comprising contacting a polyester or a composition or article-of-manufacturing comprising same with a catalyst system that forms an organometallic complex as defined in any one of claims 1 to 29 under a condition that effects degradation of the polyester to the cyclic ester that composes it, to thereby obtain said cyclic ester; subjecting said cyclic ester to a condition that effects ring opening polymerization, thereby obtaining a recycled polyester;optionally integrating the recycled polyester in a composition or an article-of- manufacturing; and optionally repeating said contacting with said catalysts system to thereby obtain said cyclic ester, and thereafter subjecting the recycled polyester or the composition or article-of- manufacturing comprising same to a condition that effects degradation of the polyester.

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