Depolymerization of poly(ethersulfone)

Abstract

A process for depolymerizing a polymer material, the process comprising: forming, in a reactor vessel, a reaction medium comprising DMSO, water, an alkali compound being NaOH, and at least one PES polymer comprising at least 80 mol% of recurring units of formula (I) based on the total amount of moles of recurring units in the PES polymer; and reacting the at least one PES polymer with the alkali compound to form a depolymerized material comprising bisphenol S of formula (II), with a yield of at least 90% of bisphenol S, said yield being defined as the molar percent of bisphenol S in the depolymerized material based on the initial molar amount of PES polymer added to the reaction vessel. The volumetric ratio of DMSO / water in the reaction medium is preferably at least 10:1 and at most 150:1, and the alkali compound amount is preferably at least 2 Eq. and at most 7 Eq. based on the initial molar anount of the PES polymer present in the reaction medium.

Description

Depolymerization of Poly(ethersulfone) Cross-Reference to Related Applications

[0001] This application claims priority to European application No.23307257.8 filed on December 19, 2023, the whole content of this application being incorporated herein by reference for all purposes. Technical Field

[0002] The present disclosure relates to a depolymerization process starting from polyethersulfone (PES polymer) as a feedstock to produce recycled 4,4’-hydroxy bisphenol S, which is suitable as a reactant to manufacture sulfone polymers. Background Art

[0003] Products made from or incorporating polymers are a part of almost any workplace or home environment. Generally, the polymers that are used to create these products are formed from virgin polymer materials. That is, the polymers are produced from petroleum and are not made from existing polymer materials. Once the products have outlived their useful lives, they are generally sent to waste disposal or a recycling plant.

[0004] The omnipresence of polymers and the importance of environmental policy have led to the increased importance of recycled polymer materials. Virgin polymer composition replacement is considered to represent a significant way forward to solve the global polymer waste problem, stop the depletion of limited natural resources, and facilitate a circular economy. Recycling is one of the most significant actions which aims to reduce fossil oil usage, carbon dioxide emissions, the hazards associated with waste disposal, and the high rates of polymer pollution.

[0005] Polymer recycling has a variety of benefits over creating virgin polymer from petroleum feedstocks. Generally, less energy is required to manufacture an article from recycled polymer materials derived from post-consumer and post-industrial waste materials and polymer scrap (collectively referred to in this specification as “waste polymer material”) than from the comparable virgin polymer. Recycling polymer materials obviates the need for disposing of polymer materials or products.

[0006] Generally, there are two ways to recycle polymers: physical recovery and chemical recovery. Mechanical recycling, also known as secondary recycling without changing the basic structure of the material, is a process of recovering SSPU 2023 / 023waste polymer material for re-use in manufacturing polymer products via mechanical means. Compared to chemical recycling, mechanical recycling is more ideal, especially when the polymer to be mechanically recycled is available in large amounts, is free from fillers and impurities / additives, is comprised of only one polymer type, and has not been partially decomposed during its life cycle. However, the availability of clean, filler / additive free, and single polymer- based material for mechanical recyclability is low. Furthermore, most polymers naturally degrade over the course of their life-cycle due to normal thermo- oxidative or UV induced processes resulting in marked decreases in polymer molecular weight. Since molecular weight is correlated to mechanical properties – it is therefore challenging to obtain an end-of-life part possessing the same mechanical properties following mechanical recycling. Chemical recycling is a term used to describe chemical processes that transform high molecualar weight polymers into smaller molecules and monomers - usually, liquids or gases - which can be re-used as a feedstock for the production of new petrochemicals and polymers. For most polymers, many chemical recycling methods lead to products other than the constituent monomers, meaning that such recycling methods lack the ability to produce components that are able to be direcly repolymerized back to the same polymer.

[0007] Given the demand for improved sustainability and circular economy, recycling a polymer back into the same application for which it is intended is highly desired. Such recycling can be viewed as efficient resource utilization where no waste is generated and the polymer is cycled back into the same application that generated it as waste (after its initial use) in the first place. Such a recycling process would be eco-friendly with high efficiency. This would be an improvement over incumbent technologies in which polymers are recycled for less demanding applications thus limiting their end-use. Polymers reuse in their originally intended application is in general quite limited.

[0008] The amorphous sulfone polymers are successfully used in various applications such as automotive, aircraft interiors, coatings, composites, electronic equipment, fittings and manifolds, faucet components, food service, fuel systems, membranes, medical and dental devices, orthopedics, sterilization cases and trays, and additional aerospace applications because the sulfone polymers exhibit a unique property profile that includes high strength, toughness, high temperature resistance, resistant to steam in sterilizaiton processes, and are inherently flame retardant and transparent in addition to other attributes. They are also considered to have good biocompatibility – meaning they have a minimal impact on clotting factor for blood when used in membrane applications. As a result, they find SSPU 2023 / 023broad utility in medical devices where steam sterilization is needed, water filtration and hemodialysis membranes among other applications including plumbing and aerospace. For that reason, they are particularly applied in hemodialysis membranes, reverse-osmosis membranes, plumbing forms such as pipes and baby bottles.

[0009] As a consequence of their wide-spread use, there is an increase in industrial waste and end-of-life products containing polyarylether sulfone (PAES) polymers, and in lieu of being discarded, there is an increasing interest in recent years in recycling such PAES polymeric materials.

[0010] However the PAES polymers are relatively difficult to be decomposed due to their excellent chemical resistance and heat resistance. A few decomposition methods applicable to chemical recycling of PAES polymers have been studied, however these methods lead to products other than monomers able to be direcly repolymerized back to the same polymer.

[0011] EP0532893 (Hercules) relates to a process of preparing a reactive reduced molecular weight polyarylene polyether from a starting polyarylene polyether, in particular a PAES polymer, which includes contacting the starting polyarylene polyether with a nucleophilic reagent for a period of time sufficient to reduce the molecular weight of the starting polyarylene polyether, and then recovering the reactive reduced molecular weight polyarylene polyether. The most preferred nucleophiles used are alkali metal hydroxides, alkali metal sulfides, alkali metal hydrogensulfides, ammonia, alkylamines, hydrazines, and thiol or amino substituted triazoles. Such reactive reduced molecular weight polyarylenes preferably have tertiary amine reactive end groups. They are intended for use in combination with various other resins including epoxy, bismaleimide, cyanate ester, phenol-formaldehyde, urethane, polyester, vinyl ester, siloxane, cyclopentadiene and higher oligomers, acetylenic, and cyclic polycarbonate resins, or mixtures thereof. For example, a polyethersulfone ‘PES’ (Starting Polymer C) having a Mw of 35,000 is decomposed into a reduced molecular weight PES of a Mw from 5780 to 10,100 (see Ex.3, 8, 11, 12). Such a process does not provide a suitable yield in Bisphenol S.

[0012] JP2009173902A (Sumitomo) relates to a decomposition method for decomposing the aromatic ether compound with a basic compound having a ≥ 14 acid dissociation constant (pKa) at 25 °C in the presence of a solvent. Among the basic compounds, quaternary ammonium hydroxide, alkali metal alkoxide, or alkaline earth metal alkoxide are particularly preferable. However, decomposition of a PES polymer (Example 1) led to a low yield of Bisphenol S. SSPU 2023 / 023Summary of invention

[0013] The present invention addresses the recyclability of sulfone polymers where the PES polymer is effectively depolymerized into constituent monomer units with a high yield in the reaction medium. By using sodium hydroxide (NaOH) to react with the PES polymer dissolved in dimethylsulfoxide (DMSO) and in the presence of water, the resulting reaction medium forms a depolymerized material, which includes bisphenol S. As would be appreciated by those of ordinary skill in the art, bisphenol S is a key monomer used to manufacture a PES polymer. In such a manner, the PES polymer provided to the reaction medium can be converted into bisphenol S which can subsequently be recycled to manufacture additional PES polymer or could be applied as a feedstock for other end uses.

[0014] One aspect of the present invention relates to a process for depolymerizing a polymer material, the process comprises: providing in a reaction vessel a reaction medium comprising DMSO, NaOH, water, and at least one PES polymer comprising at least 80 mol% based on the total amount of moles of recurring units in the PES polymer, of recurring units of formula (I); and reacting the at least one PES polymer with NaOH to form a depolymerized material comprising bisphenol S of formula (II), with a yield of at least 90% of bisphenol S, said yield being based on the initial (molar) amount of the PES polymer present in the reaction medium. Detailed Description of the present invention

[0015] Definitions

[0016] In the present application: - any description, even if described in relation to a specific embodiment, is applicable to and interchangeable with other embodiments of the present disclosure, and each embodiment thus defined may be combined with another embodiment, unless otherwise indicated or clearly incompatible; - where an element or component is said to be included in and / or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individuals recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components; any element or component recited in a list of elements or components may be omitted from such list; - any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited ranges as well as the endpoints of the range and equivalents; SSPU 2023 / 023- the term "comprising" (or “comprise”) includes "consisting essentially of" (or “consist essentially of”) and also "consisting of" (or “consist of”); and - the use of the singular ‘a’ or ‘one’ herein includes the plural unless specifically stated otherwise; and - it should be understood that the elements, properties, and / or the characteristics of a (co)polymer, product or article, a process, or a use, described in the present specification, may be combined in all possible ways with the other elements, properties and / or characteristics of the (co)polymer, product or article, process or use, explicitly or implicitly, this being done without departing from the scope of the present description.

[0017] The term "solvent" is used herein in its usual meaning, that is, it indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level. In the case of a polymeric solute, it is common practice to refer to a solution of the polymer in a solvent when the resulting mixture is transparent and no phase separation is visible in the system. Phase separation is taken to be the point, often referred to as the "cloud point", at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.

[0018] The term "membrane" is used herein in its usual meaning, that is to say, it refers to a discrete, generally thin, interface that moderates the permeation of chemical species in contact with it. A membrane generally comprises a polymeric material. Examples of membranes are water purification membranes and hemodialysis membranes.

[0019] The term “post-consumer” polymeric material (or article) refers to a finished good that is used and then recycled; this may provide a source of polymeric material that can be used in the present method. The typical post-consumer polymeric material may include, but is not limited to, packaging, membranes (e.g., dialysis membranes or reverse osmosis (RO) membranes), compounds, automotive components, electronic components, consumer product components such as but not limited to plumbing forms (e.g., plastic bottles and particularly baby bottles), battery components, or any used or end-of-life three-dimensional injection- molded, extruded or printed articles or parts thereof.

[0020] The term “post-industrial” polymeric material (or article), also known as “pre- consumer” polymeric material (or article), refers to waste generated from manufacturing processes that lead to the creation of the source polymeric material which can be used in the present method. For example, when a polymer is formed into bottles, polymeric scraps may be generated and they do not end up in the final bottle products. If these polymeric scraps are ground, shredded, or re- pelletized, and used again in making the same article or another article, they will SSPU 2023 / 023be referred to as “post-industrial” polymeric material. Typical pre-consumer polymeric material may include, but is not limited to, whole articles, parts thereof, or scraps thereof, of packaging, films, fibers, membranes, off-specification compounds, or polymeric products including off-specification polyarylethersulfones, automotive components, electronic components, consumer product components such as plastic bottles and particularly baby bottles, battery components, or any three-dimensional injection-molded, extruded or printed articles or parts thereof.

[0021] In other words, post-consumer polymeric material (or article or waste) refers to finished goods, while post-industrial polymeric material (or article or waste) refers to waste material generated from a manufacturing process that manufactures polymers or polymeric based articles.

[0022] The weight average molecular weight (Mw) and the number average molecular weight (Mn) may be estimated by gel-permeation chromatography (GPC), also known as Size Exclusion Chromatography, calibrated with polystyrene standards. The mobile phase may be selected from any suitable solvent for the polymer described herein, for example, the solvent(s) described herein, such as methylene chloride, N-alkyl-2-pyrrolidone like N-methyl-2-pyrrolidone (NMP), N-butyl-2- pyrrolidinone, etc., dimethyl sulfoxide (DMSO), 1,3-dimethyl-2-imidazolidinone (DMI), tetramethylene sulfone (sulfolane), N,N′-dimethylacetamide (DMAc) or any mixture thereof, preferably DMSO or methylene chloride. The polydispersity index (PDI), or dispersity (Ð), is hereby expressed as the ratio of weight average molecular weight (Mw) to the number average molecular weight (Mn).

[0023] Should the disclosure of any patents, patent applications, and publications that are incorporated herein by reference conflicts with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0024] Disclosure of preferred embodiments

[0025] An aspect of the present invention relates to a process for depolymerizing a polymeric material, the process comprising: forming, in a reactor vessel, a reaction medium comprising DMSO, water, NaOH, and at least one PES polymer comprising at least 80 mol%, based on the total amount of moles of recurring units in the PES polymer, of recurring units of formula (I); and reacting the at least one PES polymer with NaOH to form a depolymerized mixture comprising bisphenol S of formula (II), preferably of formula (II’), with a yield of at least 90% of bisphenol S, said yield being based on the initial (molar) amount of PES polymer in the reaction medium. SSPU 2023 / 023

[0026] The yield of Bisphenol S may be measured as can be defined as the molar percent of bisphenol S in the depolymerized material based on the initial molar amount of PES polymer added to the reaction vessel.

[0027] The polyethersulfone (PES) polymer

[0028] The polyethersulfone polymer, hereinafter referred to as “PES polymer” which is used as a reactant in the process of the present invention is a polymer comprising at least 80 mol.%, based on the total number of moles of recurring units of PES polymer, of a recurring unit (RPES) of formula (I):

[0029] The PES polymer may be a homopolymer having only one recurring unit (RPES) of formula (I), or may be a copolymer comprising two or more recurring units, one of which being of the formula (I) along with at least one different recurring unit.

[0030] The PES polymer may comprise at least 85 mol%, at least 90 mol%, at least 95 mol%, at least 99 mol%, or even 100 mol% of recurring units (RPES) of formula (I) based on the total number of moles of recurring units in the PES polymer.

[0031] The PES polymer may be produced by a variety of methods. The PES polymer is preferably derived by polycondensation from at least one aromatic diol monomer and at least one aromatic dihalo monomer, more preferably derived by polycondensation.of bisphenol S and dichlorodiphenyl sulfone

[0032] For example, U.S. Pat. Nos.4,108,837 and 4,175,175 describe the preparation of polyarylethers and in particular polyarylethersulfones. Several one-step and two- step processes are described in these patents, which patents are incorporated herein by reference in their entireties. In these processes, a double alkali metal salt of a dihydric phenol is reacted with a dihalobenzenoid compound in the presence of a polar aprotic solvent under substantially anhydrous conditions. In a two-step process, the aromatic diol is first converted, in situ, in the presence of the solvent to the alkali metal salt derivative by reaction with an alkali metal or an alkali metal compound. An alkali metal salt is produced as a byproduct of the polymerization.

[0033] The weight average molecular weight Mw of the PES polymer may be from 30,000 to 100,000 g / mol, for example from 35,000 to 90,000 g / mol or from 40,000 to 85,000 g / mol. The weight average molecular weight (Mw) of PES polymer can be determined by gel permeation chromatography (GPC) using methylene chloride as a mobile phase calibrated with polystyrene standards. SSPU 2023 / 023Examplary GPC conditions may be as follows: 2x 5µ mixed D columns with guard column from Agilent Technologies; flow rate: 1.5 mL / min; injection volume: 20 µL of a 0.2w / v% sample solution.

[0034] Source of the PES polymer

[0035] The source of the PES polymer added to the reaction medium may be pure PES polymer or in the form of a polymeric material. The source of the PES polymer to be added to the reaction medium in the process of the present invention may be considered a waste, such as end-of-life products, industrial scraps, and / or unsalable (e.g., off-specification, surplus) products or articles.

[0036] The PES polymer can be added to the reactor vessel in solid form, such as pellets, fibers, flakes, powder, pieces of shredded or ground articles, coagulated particles, or any other solid 3-D objects, or in form of a solution or slurry in which at least part of the PES polymer is dissolved in DMSO before being depolymerized.

[0037] The source of the PES polymer preferably comprises at least one material selected from the group consisting of post-consumer polymeric articles, post-industrial polymeric articles or parts thereof, off-specification polyarylethersulfone products; and any combination thereof. The source of the PES polymer may comprise, or consist of, at least one material selected from the group consisting of membranes, composites, battery components, plastic bottles such as baby bottles, any parts or scraps thereof, and any combination thereof.

[0038] The source of the PES polymer may comprise at least 50% by weight (wt.%), based on the total weight of the polymeric material, of the PES polymer. The source of the PES polymer preferably comprises at least 55% wt.%, at least 60% wt.%, at least 65% wt.%, at least 70% wt.%, at least 75% wt.%, at least 80% wt.%, at least 85% wt.%, at least 90% wt.%, at least 95% wt.% or at least 99% wt.% the PES polymer, based on the total weight of the source of the PES polymer.

[0039] The source of the PES polymer may consist essentially of at least one PES polymer. It is understood that more than one PES polymers may be included in the source of PES polymer. As used herein, the term “consisting essentially of” means that any additional component is present in an amount of at most 1% by weight, based on the total weight of the source of the PES polymer.

[0040] In alternate embodiments, the source of the PES polymer may comprise at least one PES polymer and at least one additional component.

[0041] Alkali compound

[0042] Without wishing to be bound by any particular scientific theory, Applicant understands that the alkali compound is used in the reaction medium in the presence of water to hydolyse the PES polymer into Bisphenol S. The alkali compound SSPU 2023 / 023further acts to deprotonate the Bisphenol S to form the sodium salt of Bisphenol S. In the present case, the alkali compound is NaOH. As provided in the examples, the use of other alkali compounds such as KOH, CsOH and tetramethylammonium hydroxide (TMAOH) did not provide a comparatively high yield of Bisphenol S.

[0043] The amount of the alkali compound (NaOH) used in the depolymerisation is determined based on the total number of oxygen atoms (the total number of oxygen equivalents) forming the ether bonds of the PES polymer. It should be used in the range of 1 to 10 equivalents, preferably in the range of 2 to 8 equivalents, more preferably 2 to 5 equivalents, and even more preferably 2 to 4 equivalents relative to the total number of oxygen equivalents of the aromatic ether compound (PES) as the substrate. Most preferably, the amount of the alkali compound (NaOH) used in the depolymerisation is in the range of 2 to 3.5 equivalents.

[0044] For illustration purposes, when the PES polymer consists of recurring units (RPES) of formula (I) which has a formula weight of 232 g / mol and 1 oxygem atom forming an ether bond per recurring unit (RPES), 1 oxygen equivalent for 1 g of PES polymer to be depolymerized corresponds to 4.1 mmol oxygen atoms, the calculation being shown below: 1 Eq. O = 1 g PES / 232 g RPES / mol RPES* 1 mol O / g RPES =4.1 mmol O. In such instance, an amount of 2 equivalents for the alkali compound (NaOH) would mean using 8.2 mmol of NaOH in the depolymerization.

[0045] The NaOH and the PES polymer can be present in the reaction medium in a molar ratio of NaOH to oxygen atoms forming ether bonds in the PES polymer of at least 2:1, and at most 8:1, preferably at most 7:1, or at most 6:1, or at most 5:1, or at most 4.5:1.

[0046] Polar aprotic solvent

[0047] The polar aprotic solvent is preferably selected such that the PES polymer is soluble in this solvent. In the present case, the polar aprotic solvent is dimethylsulfoxide (DMSO).

[0048] As shown in the examples, the use of other polar aprotic solvents such as diphenylsulfone (Ph2SO), dimethylacetamide (DMAc), dimethylformamide (DMF), N,N′-dimethylpropyleneurea (DMPU) or combination of any of them with DMSO did not provide a comparatively high yield of Bisphenol S.

[0049] The amount of the polar aprotic solvent may be optimized as appropriate depending on the type of PAES polymer and / or alkali compound used in the depolymerisation. When the PAES polymer is dissolved in the polar aprotic solvent, it is preferable to determine the amount of the solvent used so that the PAES polymer can be completely dissolved in the range of 1 wt.% to 10 wt.%. It SSPU 2023 / 023is particularly preferable to determine the amount of the polar aprotic solvent used so that the PAES polymer can be dissolved in the range of 1 to 9 wt.%, or in the range of 2 to 8 wt.%, or in the range of 3 to 7 wt.%. The polar aprotic solvent may be used in an amount of from 8 to 100 parts by weight (pbw), preferably from 9 to 99 pbw, or from 10 to 99 pbw, or from 10 to 49 pbw, or from 11 to 49 parts, or from 12 to 49 pbw, or from 13 to 33 pbw, or from 15 to 24 pbw, with respect to 1 pbw of the PAES polymer.

[0050] The DMSO and water can be present in the reaction medium in a volumetric ratio of DMSO to water of at least 10:1, preferably at least 15:1, or at least 20:1, and at most 150:1, preferably at most 140:1, or at most 130:1, or at most 120:1, or at most 110:1, or at most 100:1.

[0051] Process description

[0052] Forming the reaction medium in the process

[0053] The various components of the reaction medium (that is to say, the PES polymer source, water, NaOH as the alkali compound and DMSO as the polar aprotic solvent, and any other optional components) may be added simultaneously or sequentially.

[0054] Preferably the PES is loaded first into the reactor vessel with the solvent to be dissolved, and then NaOH is added either alone or in combination of another portion of solvent. The water may be added to the reactor vessel after or preferably during the PES dissolution, and / or may be added to the reactor vessel at the same time as when the NaOH is loaded.

[0055] In some cases, the PES polymer may be added to the reactor vessel in solid form, such as pellets, fibers, powder, flakes, pieces of shredded or ground articles, coagulated solids (e.g., coagulated polymer beads, particles, or prills), any other solid 3-D objects, or any mixture thereof. The pellets for example may be in any shape, such as cylindrical, spherical, or ovoid. In particular, when a PES polymer source may comprise a post-industrial waste from a polyarylethersulfone manufacturing plant, such waste may be obtained after a coagulation step (in coagulated form) and subsequently not dried before being recycled and used as a reactant in the current process. The shape and size of the PES polymer are not critical so long as the PES polymer can dissolve, at least in part, preferably completely, in DMSO which is the preferred polar aprotic solvent.

[0056] In some embodiments, the PES polymer which is in solid form is “pre-dissolved” in the reactor vessel with some or all of DMSO. In such instances, the pre- dissolution may be carried out with only the PES polymer source and DMSO, and then a mixture of NaOH, DMSO and water is then added to that PES solution to form the reaction medium. In other instances, water may be added during the PES SSPU 2023 / 023pre-dissolution into DMSO before adding the NaOH to finally form the reaction medium.

[0057] It may be necessary to provide heat during PES pre-dissolution in order to facilitate the dissolution of PES polymer. The PES dissolution may be favored at a temperature of at least ambient temperature, but should not exceed the boiling point (189oC) of DMSO, preferably from 50oC to 150oC or from 70oC to 130oC. Or preferably the reaction medium can be heated to a temperature of at least 100℃, or at least 110℃, or at least 120℃ and at most 180℃ or at most 170℃, or at most 160℃, or at most 150℃. Further, the heating of the reaction medium can occur for a duration of at least 5 hours and at most 24 hours (e.g., from 6 hours to 24 hours, from 7 hours to 24 hours, from 8 hours to 24 hours, from 9 hours to 24 hours, from 10 hours to 24 hours, from 11 hours to 24 hours, or from 12 hours to 24 hours).

[0058] In alternate embodiments, the PES polymer may be added to the reactor vessel in form of a solution or slurry in which at least some of the PES polymer is “pre- dissolved” ex-situ, that is to say, not in the reactor vessel, before being added to the reactor vessel. In such instances, the PES polymer may be mixed with a polar aprotic solvent. It may be necessary to heat the mixture of the PES polymer and solvent in order to facilitate the dissolution of PES polymer into the solvent. The dissolution may be favored at a temperature of at least ambient temperature but should not exceed the boiling point of the solvent, preferably from 50oC to 150oC or from 70oC to 130oC. Such pre-dissolution would take place in a vessel separate from the reactor vessel (e.g., a feed tank). In instances when the resulting pre- dissolved PES polymer is in the form of a slurry containing solids such as insoluble fillers originating from the PES polymer source, the solids may be removed (e.g., the slurry is filtered) to recover a PES polymer solution. The PES polymer solution is then added to the reactor vessel. The polar aprotic solvent into which the PES polymer may be pre-dissolved is preferably the same polar aprotic solvent (DMSO) used in the reaction medium. Such polar aprotic solvent is particularly selected for its ability to completely dissolve the PES polymer when it is mixed ex-situ with PES polymer. While the following polar aprotic solvents such as N-alkyl-2-pyrrolidone like N-Methyl-2-pyrrolidone (NMP), N- butyl-2-pyrrolidinone, etc., dimethyl sulfoxide (DMSO), 1,3-dimethyl-2- imidazolidinone (DMI), tetramethylene sulfone (sulfolane), N,N′- dimethylacetamide (DMAc) or any mixture thereof may be suitable for pre- dissolving the PES polymer before addition to the reactor vessel, the polar aprotic solvent used for pre-dissolution of PES polymer is preferably DMSO as described above. Water may be also added during PES pre-dissolution whether it may be SSPU 2023 / 023done in situ (meaning inside the reactor vessel) or ex situ (in a separate vessel different than the reactor vessel).

[0059] In particular embodiments, the various addition steps for preparing the reaction medium may be carried out as follows:

[0060] - the PES polymer is loaded into the reactor vessel with the solvent to dissolve the PES polymer into the solvent, preferably by heating at a temperature of from ambient temperature to less than the boiling point of the solvent, preferably from 50oC to 150oC or from 70oC to 130oC, or preferably the reaction medium can be heated to a temperature of at least 100℃, or at least 110℃, or at least 120℃ and at most 180℃ or at most 170℃, or at most 160℃, or at most 150℃; and - NaOH and water are added, simultaneously or in succession, to the reactor vessel after the PES polymer is dissolved. Further, the heating of the reaction medium can occur for a duration of at least 1 hour or at least 3 hours or at least 5 hours or at most 72 hours (e.g., 3 hours to 72 hours, 6 hours to 24 hours, 7 hours to 24 hours, 8 hours to 24 hours, 9 hours to 24 hours, 10 hours to 24 hours, 11 hours to 24 hours, or 12 hours to 24 hours).

[0061] In alternate embodiments, the various addition steps for preparing the reaction medium may be carried out as follows: - the PES polymer is pre-dissolved ex-situ (i.e., in a feed tank separate from the reactor vessel) with a solvent which may be the same or different than DMSO to dissolve the PES polymer, preferably by heating at a temperature of from ambient temperature to less than the boiling point of the solvent, preferably from 50oC to 150oC or from 70oC to 130oC, preferably the reaction medium can be heated to a temperature of at least 100℃, or at least 110℃, or at least 120℃ and at most 180℃ or at most 170℃, or at most 160℃, or at most 150℃; and optionally after dissolution, filtered to remove solids; and - then the pre-dissolved PES polymer, NaOH, water and DMSO are added, simultaneously or successively, to the reactor vessel. Further, the heating of the reaction medium can occur for a duration of at least 5 hours and at most 24 hours (e.g., 6 hours to 24 hours, 7 hours to 24 hours, 8 hours to 24 hours, 9 hours to 24 hours, 10 hours to 24 hours, 11 hours to 24 hours, or 12 hours to 24 hours).

[0062] The depolymerization reaction

[0063] During the reaction, NaOH and the PES polymer can be present in the reaction medium in a molar ratio of NaOH to PES polymer of at least 2:1, and at most 8:1, preferably at most 7:1, or at most 6:1, or at most 5:1, or at most 4.5:1. The number of moles of PES in the reaction medium may be determined based on the number average molecular weight Mn of the PES polymer. SSPU 2023 / 023

[0064] The reacting step is carried out at a reaction temperature of at least 80℃, or at least 100℃, or at least 110℃, or at least 120℃ and at most 180℃, or at most 170℃, or at most 160℃, or at most 150℃. The process may further comprise the step of heating the reaction medium to reach the reaction temperature described above.

[0065] During the reaction, DMSO and water can be present in the reaction medium in a volumetric ratio of DMSO to water of at least 10:1, preferably at least 15:1, or at least 20:1, and at most 150:1, preferably at most 140:1, or at most 130:1, or at most 120:1, or at most 110:1, or at most 100:1.

[0066] The reacting step is preferably carried out in the reaction medium for a time period of at least 3 hours, or at least 6 hours, or at least 9 hours, or at least 12 hours, and at most 24 hours.

[0067] The reacting step in the process according to the invention forms a depolymerized material.

[0068] The depolymerisation reacting step in the process of the present invention may be carried out under pressure or under reduced pressure, and the pressure in the depolymerisation may be determined depending on the type of polar aprotic solvent to be used and the depolymerisation temperature. For practicality however, atmospheric pressure (about 100-102 kPa) is preferable during depolymerisation.

[0069] When the PES polymer having a polymeric chain made of recurring units (RPES) of formula (I) described above, is depolymerized in the process of the present invention, the alkali compound cleaves the ether bond –O– of the recurring units.

[0070] The depolymerized material

[0071] As used herein, the term “depolymerized material” refers to the products resulting from the hydrolytic reaction of the PES polymer with NaOH. The depolymerized material preferably comprises bisphenol S of formula (II):(II), preferably comprises bisphenol S of formula (II’) :(II’).

[0072] The depolymerized material may further comprise >0 and up to 5 wt% of an aromatic dimer of formula (III): SSPU 2023 / 023preferably may further comprise >0 and up to 5 wt% of an aromatic dihydroxy dimer of formula (III’) :

[0073] In some embodiments, the depolymerized mixure may further comprise >0 and up to 5 wt% of an oligomer of the PES polymer having recurring units of the formula (I). As used herein, an oligomer is a PES polymer having a Mn of at most 1500 g / mol (preferably measured by the1H-NMR and LC-MS techniques described in the examples section).

[0074] The number average molecular weight of the depolymerized material, defined by the bisphenol S of formula (II), the aromatic dimer of formula (III), and oligomers of the PES polymer containing recurring units of formula (I) is at most 1500 g / mol, or at most 1000 g / mol, preferably at most 900 g / mol, or at most 800 g / mol, or at most 700 g / mol, or at most 600 g / mol, or at most 500 g / mol.

[0075] The purity of the depolymerized material is defined as the content of bisphenol S in the depolymerized material based on the total weight of the depolymerized material. The depolymerized material can have a Bisphenol S purity of at least 95 wt%, preferably at least 97 wt%, or at least 98 wt%, or at least 99 wt%.

[0076] The yield of bisphenol S produced by the process according to the invention can be defined as the molar percent of bisphenol S in the depolymerized material based on the initial molar amount of PES polymer added to the reaction vessel. The yield of bisphenol S is preferably at least 90%, or at least 95%, or at least 98%, or at least 99%.

[0077] Termination of depolymerisation

[0078] To stop the depolymerisation reaction, the now-formed depolymerized material is preferably cooled to reduce the temperature to less than 80oC, preferably less than 60oC, or less than 50oC, or less than 40oC, or less than 30oC or less than 20oC, or less than 10oC.

[0079] Acid treatment

[0080] In preferred embodiments, after the reaction has completed in the reactor vessel, the cooled depolymerized material may be subjected to an acid treatment. For instance, the depolymerized material can be acidified with an acid (preferably a mineral acid such as HCl). As would be appreciated by those of skilled in the art, SSPU 2023 / 023not only does this acid treatment result in lowering the pH to less than 5, and preferably less than 4, or less than 3, or less than 2, or less than 1.5, or preferably to about 1, but it also converts the sodium salts of bisphenol S represented by formula (II), present in the depolymerized material and obtained by the reaction between the PES polymer with NaOH, to form the protonated bisphenol S monomer represented by formula (II’).

[0081] Precipitation

[0082] In particular embodiments, the acidified depolymerized material is subsequently subjected to precipitation into a non-solvent or poor solvent (such as water) that does not readily dissolve PES polymeric / oligomeric / dimeric materials, but does significantly solubilize Bisphenol S monomer represented by formula (II’). Such a precipitation therefore results in the formation of a precipitate containing mostly PES oligomeric / dimeric materials and residual unreacted PES polymer while also forming a liquid supernate containing dissolved Bisphenol S of formula (II’).

[0083] Solid / liquid separation

[0084] After precipitation, a solid / liquid separation is preferably carried out to remove the precipitate. The solid / liquid separation preferably includes filtration, but other solid / liquid separation techniques may be employed. The filtering can be performed in a variety of ways, such as vacuum filtering or any form of filtering as desired. As it would be appreciated by those of ordinary skill in the art, a portion of the resulting depolymerized material will be in a solid form (precipitate) while another portion of the depolymerized material will be in solution (supernate). The supernate thus should contain the liquid components used in the reaction medium and used in precipitation (non-solvent / poor solvent), such as water and DMSO and Bisphenol S, which is preferably of formula (II’), in soluble form. When the solid / liquid separation includes filtration, the precipitate is recoved as the filtered solid and the supernate is recovered as the filtrate.

[0085] Optional drying of precipitate

[0086] This precipitate (e.g, filtered solid) may be dried at a temperature from 80 to 120 °C, preferably 90 to 110°C, preferably at 100°C. This dried precipitate (e.g, filtered solid) may be referred to as the solid byproduct. This solid byproduct which can be characterized using1H-NMR spectroscopy generally contains PES oligomers or dimers such as those of formula (III) or (III’). The higher the depolymerisation yield proceeds towards Bisphenol S, a lesser amount of solid byproduct should be obtained after acidification and precipitation of the depolymerized material.

[0087] Recovery of Bisphenol S from the liquid supernate SSPU 2023 / 023

[0088] The liquid supernate (e.g., filtrate) obtained after acidification and precipitation of the depolymerized material generally comprises the majority of the formed Bisphenol S, and this Bisphenol S (preferably of formula (II’)) is dissolved in the water / DMSO mixture or in water / DMSO / non-solvent mixture in instances when the non-solvent used in precipitation is not water.

[0089] This liquid supernate (e.g., filtrate) may be extracted with ethyl acetate (EtOAc), or other similar polar solvents (such as ethers), and the extraction is preferably repeated several times (such as 3 times). The organic phase resulting from such extraction may be then dried over a chemical dessicant such as NaSO4, filtered and the remaining solvent is evaporated to dryness under reduced pressure such as in a rotary evaporation system (40 °C, 180 mbar). The recovered solid obtained from extraction of the liquid supernate (eg, filtrate) provides the Bisphenol S product. The purity of the Bisphenol S product can be confirmed by1H-NMR spectroscopy and LC-MS analysis. Examples

[0090] The invention will be now described in more detail with reference to the following examples whose purpose is merely illustrative and not limitative of the scope of the invention. As used in the Examples, “E” denotes an embodiment of the present invention and “CE” denotes a counter-example.

[0091] Raw Materials SSPU 2023 / 023Table I. Chemical (Abbreviation) Supplier Product Name from Supplier / Characteristics Solvay Veradel® 3000P – (Mw= 85,000 Sp g / mol ; Mn= 45,200 g / mol ; PDI Polyethersulfone (PES) ecialty Polymers =1.88; measured via SEC (GPC) in USA DMSO using polystyrene standards) Sodium hydroxide (NaOH) ≥98 %, pellets Potassium hydroxide (KOH) ≥85 %, pellets Cesium hydroxide (CsOH.H2O) ≥ 90 % Tetramethylammonium hydroxide (TMAOH.5H2O) ≥ 97 % Dimethylsulfoxide (DMSO) Sigma- Anhydrous Dimethylacetamide (DMAc) Aldrich Anhydrous Diphenyl sulfone (Ph2SO) 96 %, solid Dimethylformamide (DMF) Anhydrous Dimethylpropyleneurea (DMPU) Anhydrous Ethylene Acetate (EtOAc) Technical grade Sodium sulfate (NaSO4) Technical grade

[0092] General Procedure 1

[0093] In this procedure 1, all of the components (PES, solvent, water) of the reaction mixture except the alkali compound (preferably NaOH) were first added to a reactor vessel to make an homogenous PES solution, and then the alkali compound (generally, solid NaOH) was added to such PES solution to finally form the reaction medium.

[0094] The Procedure 1 was used for most of the experiments, except for experiments no. 14, 16, 18, 20.

[0095] PES (1.0 g, 4.3 mmol, 1 eq) was mixed in a solvent (20 mL) which is generally DMSO in a 250 mL three-necked round bottom flask to achieve dispersion. The mixture was heated under air to 100 °C to dissolve the PES and obtain a homogeneous PES solution. Once the PES was dissolved, deionized water (1 mL) was added to the solution, and if / when the PES precipitated after water addition, the PES slowly re-dissolved. The volumetric ratio of solvent:water used in this process was then 20:1. SSPU 2023 / 023

[0096] Once all the PES was fully dissolved, NaOH (grounded pellets, 344 mg, 8.6 mmol, 2 eq) was added as a solid all at once into the solution. The reaction medium quickly became yellow and was stirred at 100 °C for 24 hours. The term “eq” for NaOH refers to the molar amount of NaOH relative to the initial molar amount of oxygen atoms forming ether bonds in the PES. In this procedure, when 1 g PES was used, this coresponded to 4.3 mmol -O- = 1 oxygen Eq. in the PES, 2 eq of NaOH corresponds to 2 x 4.3 = 8.6 mmol NaOH. (4.3 mmol -O- in 1 gram of PES being calculated based on the formula weight of 232 g / mol for the unit (RPES) of formula (I) and 1 mol -O- per mol of unit of formula (I)]. When it was desired to have a NaOH Eq. from >2 and up to 5.6, the amount of NaOH was increased accordingly.

[0097] After a suitable time of reaction (from 3 to 24 hours), the reaction medium comprising the depolymerized material was then cooled to 0 °C using an iced bath. The cooled mixture was then acidified with hydrochloric acid (2 M HCl) until pH reached ~1 (~20 mL), to convert the sodium salt of Bisphenol S (of formula (II)) to its protonated form (see formula (II’)). If any alkali salt of dimers and oligomers were present in the depolymerized material, they also were converted to their respective protonated forms.

[0098] The acidified mixture was then poured into 50 mL of water which resulted in coagulation of polymeric / oligomeric / dimeric material, resulting in the formation of a precipitate. The resulting slurry was then filtered with a paper filter (round shaped (at the size of the Buchner filter) Whatman filter paper grade 40 without ashes) under vacuum (Buchner apparatus) to recover a solid and a filtrate. This filtered solid was then dried at 100 °C for 18 hours. This filtered solid is referred to as the solid byproduct. This solid byproduct was analysed by1H-NMR spectroscopy and generally corresponded to oligomers or dimer. The higher the depolymerisation yield was towards Bisphenol S, the lower the amount of solid byproduct was obtained after acidification and precipitation of the depolymerized material.

[0099] The filtrate obtained following acidification and precipitation of the depolymerized material generally comprised the majority, if not all, of the formed Bisphenol S which remained in dissolved form.

[0100] This filtrate was then extracted three times with EtOAc (3 x 50 mL), the organic phase dried over NaSO4, filtered on cotton, and the solvent was evaporated to dryness under reduced pressure in a rotary evaporation system (40 °C, 180 mbar). The solid obtained from the filtrate was found to correspond to the Bisphenol S as characterized by1H-NMR spectroscopy and LC-MS analysis. For example a recovery of 1.06 g = 4.26 mmol of Bisphenol S corresponded to a Bisphenol S yield of 99% (=4.26 mmol Bisphenol S / 4.3 mmol initial PES). SSPU 2023 / 023

[0101] General Procedure 2

[0102] In procedure 2, the PES was placed in a reactor vessel and dissolved to make an homogenous PES solution. Here, the solvent used for PES dissolution was not DMSO. Then the alkali compound, which was pre-mixed in 4 Eq. of DMSO and some water was added to such PES solution to finally form the reaction medium.

[0103] In the case of the experiments no.14, 16, 18 and 20 in which the solvent used for PES dissolution was selected from Ph2SO, DMAc, DMF, or DMPU, this alternate procedure 2 was carried out as follows.

[0104] PES (1.0 g, 4.3 mmol, 1 eq) was mixed in 20 mL of the selected solvent different than DMSO in a 250 mL three-necked round bottom flask to achieve dispersion. The mixture was heated up under air to 100 °C to dissolve the PES and obtain a homogeneous PES solution.

[0105] In another small vial (50 mL), DMSO (1.2 mL, 17.2 mmol, 4 eq) was mixed with solid NaOH (344 mg, 8.6 mmol, 2 eq) and deionized water (1 mL). This mixture was stirred for 1 hour at 100 °C. This NaOH mixture was then added to the homogeneous solution of PES dissolved in the selected solvent (different than DMSO). The reaction medium quickly became yellow.

[0106] The reaction medium was stirred at 100 °C for 24 hours. After the suitable time of reaction (24 hours), the reaction medium which now formed the depolymerized material was then cooled to 0 °C with an iced bath.

[0107] The cooled material was then acidified with hydrochloric acid (2 M HCl) until pH reached about 1 (~20 mL). This acidification resulted in converting the sodium salt of Bisphenol S (of formula (II)) to its protonated form of formula (II’). If any alkali salt of dimers and PES oligomers are present in the depolymerized material, they would also be converted to their respective protonated forms.

[0108] The acidified material was then poured into 50 mL of water which resulted in coagulation of polymeric / oligomeric / dimeric material so that a precipitate formed. The resulting slurry was filtered with a paper filter (round shaped (at the size of the Buchner filter) Whatman filter paper grade 40 without ashes) under vacuum (Buchner apparatus) to recover a filtered solid and a filtrate. This filtered solid was dried at 100 °C for 18 hours. This filtered solid may be referred to as the solid byproduct. This solid byproduct was analysed by1H -NMR spectroscopy and generally corresponded to oligomers of Mn size of at most 750 g / mol or dimer of size at most 500 g / mol. The higher the depolymerisation yield was towards Bisphenol S, the lesser amount of solid byproduct was obtained after acidification and precipitation of the depolymerized material. SSPU 2023 / 023

[0109] The filtrate obtained after acidification and precipitation of the depolymerized material generally comprised the majority, if not all, of the formed Bisphenol S which remained in dissolved form.

[0110] This filtrate was then extracted three times with EtOAc (50 mL each time). The organic phase was then dried over NaSO4, filtered on cotton and the solvent was evaporated to dryness under reduced pressure in a rotary evaporation system (40 °C, 180 mbar). The solid obtained from the filtrate corresponded to a Bisphenol S product as confirmed by1H-NMR spectroscopy and LC-MS analysis. For example a recovery of 0.96 g = 3.87 mmol of Bisphenol S corresponded to a Bisphenol S yield of 90% (=3.87mmol Bisphenol S / 4.3 mmol PES).

[0111] Analytical Methods

[0112] NMR spectroscopy 5 mg of a solid sample was dissolved in 0.6 mL of DMSO-d6in a 5 mm NMR tube. The product was analysed using a 300 MHz spectrometer from Brucker

[0113] LC-MS Solution prepared with 1 mg.mL-1in acetonitrile (ACN). Column Phenomex – Luna Omega C18, 50 x 2.1 mm; 1.6 µm. Mobile phase: MeOH / ACN (50 / 50) + 0.1 % formic acid Flow rate: 500 µL / min; Injection volume 2 µL

[0114] In the following tests, different alkali compounds, different solvents, different reaction temperatures and times, different alkali contents (in term of Equivalence with respect to PES molar amount), and different DMSO / water volumetric ratios were investigated.

[0115] In Table II, the alkali compounds NaOH, CsOH, KOH, TMAOH were compared.

[0116] In Table II, the following solvents: DMSO, diphenylsulfone (Ph2SO), dimethylacetamide (DMAc), dimethylformamide (DMF), N,N′- dimethylpropyleneurea (DMPU) or combination of any of them with DMSO were compared.

[0117] In Table II, the reaction time was 5 or 24 hours; the reaction temperature was room temperature (RT), 60 or 100oC; and the alkali compound content was from 1 to 5.6 Eq. relative to the initial PES molar amount.

[0118] The DMSO / water volumetric ratios of 20:1 and 500:1 were compared.

[0119] Table II provides the degree of polymerization and the obtained Bisphenol S yield (%) for the examples of the process according to the invention and counter- examples employing unoptimized reaction parameters for alkali salt forming material, solvent, reaction temperature, and reaction time. SSPU 2023 / 023Table II.. Nature Degree Rea Filtered of Obtained Tests Base Eq.Temp ct alkaliSolvent(°C) time solid the of mass Polym Bisphenol (h) obtained eri S yield (mg) solid zation (DPn) (%) 235aCE1 / / DMSO RT 24 1000 PES (Mn = 54 600 / g.mol-1) CE 2 / / DMSO 100 24 1000 PES / CE3 NaOH 5.6 DMSO 100 5 130c Dimer +monomer / 69 %1E4 NaOH 5.6 DMSO 100 24 <1Dimer +monomer / ~ 100 %1CE5 NaOH 1 DMSO 100 5 830 Oligomer 4.75b21 %1CE6 NaOH 1 DMSO 100 24 790 Oligomer 2.25b33 %1CE7 NaOH 2 DMSO 100 5 823 Oligomer 4.25b24 %1DMSO 100 24 20Di99 %1E8 NaOH 2mer +monomer / 94 %2CE9 NaOH 2 DMSO 60 24 787 Oligomer 4.35b4 %1(4 eq)fCENaOH 2 Ph SO 1Starting 152 00 24 1000polymer / / Ph2SO CE +100 24 1Starting16NaOH 2DMSO000 polym / / ber(4 eq) CENaOHStarting 172 DMF 100 24 1000polymer / / CE DMF + DMSOStarting18NaOH 2100 24 1000 pol / / (4 eq)bymerSSPU 2023 / 023CE 19gNaOH 2 DMPU 100 24 1340 Oligomer 28.12b / DMPU CE + Dimer + 20gNaOH 2DMSO 100 24 1100 Monomer 2.32b11 %1(4 eq)f+ Trimera: Calculated from the Mnobtained by SEC (GPC) using DMSO as mobile phase and polymethylmethacrylate (PMMA) calibration;b: Calculated from NMR spectra of the filtered solid. The aromatic protons of the monomer signals are located at 7.70 ppm and 6.90 ppm while the aromatic signals of the dimer are located at 7.91 ppm, 7.77 ppm, 7.24 ppm and 6.93 ppm. Each of these signals corresponds to two protons. Therefore, one signal from each product can be integrated (for example, the 7.70 ppm signal of the monomer and the 7.24 ppm signal of the dimer) to calculate a simple ratio between these integrals to obtain the composition of the product.c: Obtained solid product and extracted product are a mixture of monomer and dimer, the yield is calculated from NMR analysis of each compound;d: Monomer remaining in DMAc;e: All compounds and solvents mixed together before addition of NaOH;f: PES dissolved in the solvent at 100 °C. NaOH dissolved in mixture DMSO / water at 100 °C. The latter solution is then added dropwise to the first;g: Reaction made on 500 mg. Filtered solid mass value was doubled for the sake of comparison ease.1: NMR yield;2: LC-MS yield

[0120] In Table III, the reaction time was set to 24 hours; the reaction temperature was set to 100oC; and the NaOH or TMAOH as alkali compound content was set to 2 Eq. relative to the initial PES molar amount.

[0121] The DMSO / water volumetric ratios of 20:1 and 500:1 were compared. In Example 1 of JP2009173902A, the solution is diluted to have 1g of PES polymer in 500 mL of DMSO, which is less concentrated than the Example 21 concentration of 1g of PES for 20 mL of DMSO. As shown in Table III, the dilution from JP2009173902A requires TMAOH to obtain any Bisphenol S, while Example 21 uses the much less harmful base of NaOH and a much lower amount of DMSO.

[0122] Table III provides the comparison between present examples and related counterexamples presented by previous work in which the depolymerisation was carried out using DMSO as solvent at a reaction temperature of 100oC SSPU 2023 / 023Table III. Eq React. Filt Nature of ests Alkali Alka DM ered Obtained T SO H2O React. the (ml) (ml) Temp. time (h) solid mass obta DPnBisphenol li (°C) (mg) ined solid S yield (%) E21 NaOH 2 20 1 100 24 20Dimer +monomer / 99 %CE NaOH 2 500 1 100 3 940 Olig8.4 22omer70 %CE TMAOH 2 500 1 100Dimer + 23*3 680monomer / 34 %*CE23: reproduction of Example 1 of JP2009173902A, except that larger amounts of ingredients were used in order to recover the depolymerized material and analyse it to provide information on the solid byproduct and estimate the Bisphenol S yield

[0123] Bisphenol S Purity:

[0124] In Table IV, the samples were dissolved in acetonitrile (ACN) and diluted to 500 ppm for analysis in a LC-UV-MS. The following parameters were used for the UPLC: • Column: Waters Acquity UPLC BEH C18 (2.1 mm x 100 mm x 1.7 µm) • Mobile phase A: water + 0.1% formic acid • Mobile phase B: acetonitrile + 0.1% formic acid • Flow rate= 0.350 mL min-1• Column temperature: 40 ⁰C • PDA wavelengths monitored: 190-500 nm • Injection volume: 2µL Time (min.) % Mobile Phase A % Mobile Phase B Initial 95 5 1.0 95 5 14.0 1 99 16.0 1 99 16.5 95 5 20.0 95 5 SSPU 2023 / 023Table IV. Comparison between present examples and related counterexamples presented by previous work Sample Bisphenol S Purity (%) CE23 65.60 E21 94.75 E8 94.42 E24* 82.86 *E24: reproduction of E21 using TMAOH instead of NaOH What is claimed is: SSPU 2023 / 023

Claims

CLAIMS 1. A process for depolymerizing a polymeric material, the process comprising: forming, in a reactor vessel, a reaction medium comprising dimethylsulfoxide (DMSO), water, sodium hydroxide (NaOH), and at least one polyethersulfone (“PES polymer”) comprising at least 80 mol%, based on the total amount of moles of recurring units in the PES polymer, of recurring units (RPES) of formula (I):and reacting the at least one PES polymer with the NaOH at a reaction temperature of at least 80℃ and at most 180℃, to form a depolymerized material comprising bisphenol S of formula (II):(II), the DMSO and water being present in the reaction medium in a volumetric ratio of DMSO to water of at least 10:1, preferably at least 15:1, or at least 20:1, and at most 150:1, preferably at most 140:1, or at most 130:1, or at most 120:1, or at most 110:1, or at most 100:1; and the amount of the NaOH being in the range from 2 to 8 equivalents, preferably from 2 to 7 equivalents, more preferably from 2 to 6 equivalents, still more preferably from 2 to 5 equivalents, said equivalent being relative to the total number of oxygen atoms (the total number of oxygen equivalents) forming ether bonds in the PES polymer.

2. The process of Claim 1, further comprising the step of heating the reaction medium to reach the reaction temperature of at least 100℃, or at least 110℃, or at least 120℃ and at most 180℃ or at most 170℃, or at most 160℃, or at most 150℃. SSPU 2023 / 0233. The process of any one of Claims 1–2, wherein the PES polymer added to the reaction vessel is in solid forms, such as pellets, fibers, flakes, powder, pieces of shredded or ground articles, coagulated particles, or any other solid 3-D objects, or in form of a solution or slurry in which at least part of the PES polymer is dissolved in DMSO before being depolymerized.

4. The process of any one of Claims 1–3, wherein the depolymerized material further comprises >0 up to 5 wt% of an aromatic dimer of formula (III):preferably further comprises >0 and up to 5 wt% of an aromatic dihydroxy dimer of formula (III’) :said wt% being based on the total weight of the depolymerized material.

5. The process of any one of Claims 1–4, wherein the number average molecular weight of the depolymerized material is at most 1000 g / mol, preferably at most 900 g / mol, or at most 800 g / mol, or at most 700 g / mol, or at most 600 g / mol, or at most 500 g / mol.

6. The process of any one of Claims 1–5, wherein the reacting step is carried out in the reaction medium for a time period of at least 3 hours and at most 24 hours.

7. The process of any one of Claims 1–6, wherein the bisphenol S in the depolymerized material has a purity of at least 95%, preferably at least 97%, or at least 98%, or at least 99%, based on the total weight of the depolymerized material. SSPU 2023 / 0238. The process of any one of Claims 1–7, wherein the yield of bisphenol S is at least 90%, or at least 95%, or at least 98%, or at least 99%, said yield being based on the initial molar amount of PES polymer present in the reaction medium. SSPU 2023 / 023

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