Polymers and methods of depolymerization of polymers using pendent groups

Abstract

The present disclosure provides for polymers and modified polymers and methods of depolymerization of polymers and modified polymers. The present disclosure provides for an efficient approach for the depolymerization of polymers pendent group activation. The present disclosure includes polymers that include a low mol% of thermolytically labile groups (e.g., phthalimide ester-containing monomers). The polymers can be synthesized via conventional radical polymerization to produce polymers that are colorless, transparent and closely resemble the unfunctionalized polymer.

Description

POLYMERS AND METHODS OF DEPOLYMERIZATION OF POLYMERS USINGPENDENT GROUPSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. provisional application entitled “COMPOSITIONS, SYSTEMS AND METHODS FOR BULK DEPOLYMERIZATION OF POLYMETHYL METHACRYLATE COPOLYMERS VIA PENDENT GROUP INITIATION” and having serial number 63 / 592,944, filed October 25, 2023, and U.S. provisional application entitled “POLYMERS AND METHODS OF DEPOLYMERIZATION OF POLYMERS USING PENDENT GROUPS” and having serial number 63 / 563,488, filed March 11 , 2024, each of which is herein incorporated by reference in their entireties.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Grant Numbers 1904631 and 1941529, awarded by the National Science Foundation; and Grant Numbers W911 NF- 17-1-0326 and W911 NF-23-1-0260, awarded by the US Army Research Office. The government has certain rights in the invention.BACKGROUND

[0003] Polymer recycling is an important area due to the increased use of polymers in most consumer products. There are two categories of polymer recycling: thermomechanical recycling and chemical recycling. Thermomechanical recycling often results in a reduction in the molecular weight and mechanical properties of the recycled polymer, while chemical recycling is an approach to convert polymer into monomer or its precursor forms.SUMMARY

[0004] The present disclosure provides for polymers and modified polymers and methods of depolymerization of polymers and modified polymers.

[0005] In an aspect, the present disclosure provides for a composition comprising: a polymer having the following structure:wherein x is about 0.25-25%, wherein y is about 75-99.75%, wherein m is 1 to 10,000, wherein each of R1andR2are independently selected from H, an alkyl group, halogen, a -ON group, a -O-alkyl group, an aryl group, wherein U is a group that forms a monomer unit selected from: amethacrylate monomer, an acrylamide monomer, a methacrylamide monomer, an acrylate monomer, a styrenic monomer, a styrenic-derivative monomer, a vinyl pyridine monomer, a maleimide monomer, a maleic anhydride-derived monomer, a vinyl ester monomer, a vinyl amide monomer, a vinyl halide monomer, a substituted acrylamide, a substituted methacrylamide, or a derivative of anyone of these, whereinR6, and R7are independently selected from H, an alkyl group, halogen, a -CN group, an-O-alkyl group, and an aryl group (the squiggly line indicates the bond to the polymer backbone).

[0006] In an aspect, the present disclosure provides for a method of depolymerization a polymer comprising one or more of the following pendent groups:wherein each R1, R2, R3, R4, R5, R6, and R7are independently selected from H, an alkyl group, halogen, a -CN group, an -O-alkyl group, and an aryl group (the squiggly line indicates the bond to the polymer backbone), heating the polymer to about 180 to 300° C, wherein the polymer is a polymer as described in one of claims 1 -6; and depolymerization of the polymer, wherein about 90% of the monomer units are recovered.BRIEF DESCRIPTION OF DRAWINGS

[0007] Further aspects of the present disclosure will be more readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings.

[0008] Figs. 1A-1 C illustrate the high extents of depolymerization (~90%) for all the P(PhthMA- co-MMA) copolymers, with as little as 1 % incorporation of PhthMA achieving ~90% depolymerization. Fig. 1A illustrates a reaction scheme for the depolymerization of PMMA copolymers. Fig. 1 B illustrates thermogravimetric traces of the PMMA copolymers. Fig. 1 C illustrates the extent of depolymerization vs. mol% incorporation of / V-(methacryloxy)phthalimide. Values for extent of depolymerization were obtained from isothermal hold data at 290 °C for 2 h (Figure 50-52).

[0009] Fig. 2A illustrates the structure of P(TCPhthMA-co-MMA) and Fig. 2B illustrates the structure of P(SMA-co-MMA) . Figs. 2C and 2D illustrate the thermogravimetric analysis (TGA) traces of the (Fig. 2C) P(TCPhthMA-co-MMA) and (Fig. 2D) P(SMA-co-MMA) copolymers with varying incorporations of the depolymerization triggerable comonomers.

[0010] Fig. 3 illustrates the extent of depolymerization vs. number average molecular weight (Mn) for the P(PhthMA-co-MMA)i% copolymers.

[0011] Figs. 4A-F illustrate the high transparency and colorless nature of the synthesized polymers. Both the P(PhthMA-co-MMA)i% and the P(SMA-co-MMA)i% thin films are colorless like that of unfunctionalized PMMA. Figs. 4A, 4C, and 4E illustrate the UV-Vis spectra of (Fig. 4A) P(PhthMA-co-MMA)5%, (Fig. 4C) P(TCPhthMA-co-MMA)5%, and (Fig. 4E) P(SMA-CO-MMA)5%. Figs. 4B, 4D, and 4F illustrate the top-down view of (Fig. 4B) P(PhthMA-co-MMA)i%, (Fig. 4D) P(TCPhthMA-co-MMA)i%, and (Fig. 4F) P(SMA-co- MMA)i% films.

[0012] Figs. 5A-C illustrate that MMA could be recovered from the bulk depolymerization and simultaneous distillation of the copolymers. Fig. 5A illustrates the reaction scheme for the bulk depolymerization of P(PhthMA-co-MMA). Fig. 5B illustrates the1H NMR spectrum of the collected MMA. Fig. 5C illustrates the size-exclusion chromatography trace of the polymer byproduct.

[0013] Fig. 6A illustrates a representation of the bulk depolymerization of P(PhthMA-co-MMA- co-EGDMA) networks. Fig. 6B illustrates the thermogravimetric analysis traces of the P(PhthMA-co-MMA-co-EGDMA) networks with varying incorporations of the dimethacrylate crosslinker.

[0014] Fig. 7 illustrates the1H NMR spectrum of / V-hydroxytetrachlorophthalimide in DMSO-d6.

[0015] Fig. 8 illustrates the13C NMR spectrum of / V-hydroxytetrachlorophthalimide in DMSO-d6.

[0016] Fig. 9 illustrates the1H NMR spectrum of / V-(methacryloxy)tetrachlorophthalimide in CDCI3.

[0017] Fig. 10 illustrates the13C NMR spectrum of / V-(methacryloxy)tetrachlorophthalimide in CDCI3.

[0018] Fig. 11 illustrates the1H NMR spectrum of / \ / -(methacryloxy)succinimide in CDCI3.

[0019] Fig. 12 illustrates the size-exclusion chromatography traces for the synthesis of P(PhthMA-co-MMA)i%.

[0020] Fig. 13 illustrates the number-average molecular weight (Mn) vs. conversion plot for the synthesis of P(PhthMA-co-MMA)i%.

[0021] Fig. 14 illustrates the size-exclusion chromatography traces for the synthesis of P(PhthMA-co-MMA)3%.

[0022] Fig. 15 illustrates the number-average molecular weight (Mn) vs. conversion plot for the synthesis of P(PhthMA-co-MMA)3%.

[0023] Fig. 16 illustrates the size-exclusion chromatography traces for the synthesis of P(PhthMA-co-MMA)5%.

[0024] Fig. 17 illustrates the number-average molecular weight (Mn) vs. conversion plot for the synthesis of P(PhthMA-co-MMA)5%.

[0025] Fig. 18 illustrates the size-exclusion chromatography traces for the synthesis of P(TCPhthMA-co-MMA)i%.

[0026] Fig. 19 illustrates the number-average molecular weight (Mn) vs. conversion plot for the synthesis of P(TCPhthMA-co-MMA)i%.

[0027] Fig. 20 illustrates the size-exclusion chromatography traces for the synthesis of P(TCPhth M A-co-M MA)3% .

[0028] Fig. 21 illustrates the number-average molecular weight ( / Wn) vs. conversion plot for the synthesis of P(TCPhthMA-co-MMA)3%.

[0029] Fig. 22 illustrates the size-exclusion chromatography traces for the synthesis of P(TCPhth M A-co-M MA)5% .

[0030] Fig. 23 illustrates the number-average molecular weight (Mn) vs. conversion for P(TCPhthMA-co-MMA)5%.

[0031] Fig. 24 illustrates the size-exclusion chromatography traces for the synthesis of P(SMA- co-MMA)i%.

[0032] Fig. 25 illustrates the number-average molecular weight (Mn) vs. conversion for P(SMA- co-MMA)i%.

[0033] Fig. 26 illustrates the size-exclusion chromatography traces for the synthesis of P(SMA- CO-MMA)3%.

[0034] Fig. 27 illustrates the number-average molecular weight (Mn) vs. conversion for P(SMA- CO-MMA)3%.

[0035] Fig. 28 illustrates the size-exclusion chromatography traces for the synthesis of P(SMA- CO-MMA)5%.

[0036] Fig. 29 illustrates the number-average molecular weight (Mn) vs. conversion for P(SMA- CO-MMA)5%.

[0037] Fig. 30 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% (Mn= 35.9 kg / mol).

[0038] Fig. 31 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% (M, = 114 kg / mol).

[0039] Fig. 32 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% ( / Wr= 255 kg / mol).

[0040] Fig. 33 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% ( / Wr= 666 kg / mol).

[0041] Fig. 34 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% (M, = 2290 kg / mol).

[0042] Fig. 35 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 76.9 kg / mol) in CDCI3.

[0043] Fig. 36 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)3% (Mn= 68.9 kg / mol) in CDCI3.

[0044] Fig. 37 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)s% (Mn= 79.6 kg / mol) in CDCI3.

[0045] Fig. 38 illustrates the1H NMR spectrum of the purified P(SMA-co-MMA)i% (Mn= 70.1 kg / mol) in CDCI3.

[0046] Fig. 39 illustrates the1H NMR spectrum of the purified P(SMA-co-MMA)3% (Mn= 69.3 kg / mol) in CDCI3.

[0047] Fig. 40 illustrates the1H NMR spectrum of the purified P(SMA-co-MMA)5% (Mn= 82.6 kg / mol) in CDCI3.

[0048] Fig. 41 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 35.9 kg / mol) in CDCI3.

[0049] Fig. 42 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 114 kg / mol) in CDCI3.

[0050] Fig. 43 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 255 kg / mol) in CDCI3.

[0051] Fig. 44 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 666 kg / mol) in CDCI3.

[0052] Fig. 45 illustrates the1H NMR spectrum of the purified P(PhthMA-co-MMA)i% (Mn= 2290 kg / mol) in CDCI3.

[0053] Figs. 46A-C illustrate a side-on view of thin films of (Fig. 46A) P(PhthMA-co-MMA)i%, (Fig. 46B) P(TCPhthMA-co-MMA)i%, and (Fig. 46C) P(SMA-co-MMA)i. / o.

[0054] Figs. 47A-B illustrate an image of bulk distillation set-up (Fig. 47A) before and (Fig. 47B) after depolymerization.

[0055] Fig. 48 illustrates the size-exclusion chromatography trace of P(PhthMA-co-MMA)i% (Mn= 30.0 kg / mol) using MMA recovered from bulk distillation.

[0056] Fig. 49 illustrates the1H NMR spectrum of the polymer byproduct from the vacuum distillation of P(PhthMA-co-MMA)i% in CDCI3.

[0057] Fig. 50 illustrates the thermogravimetric analysis displaying mass loss for depolymerization of P(PhthMA-co-MMA)i%(Mn= 76.9 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0058] Fig. 51 illustrates the thermogravimetric analysis displaying mass loss for depolymerization of P(PhthMA-co-MMA)3% (Mn= 68.9 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0059] Fig. 52 illustrates the thermogravimetric analysis displaying mass loss for depolymerization of P(PhthMA-co-MMA)5% (Mn= 69.7 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0060] Fig. 53 illustrates the TGA tandem mass spectrometry of P(PhthMA-co-MMA)i% (Mn= 76.9 kg / mol) at 25 °C.

[0061] Fig. 54 illustrates the TGA tandem mass spectrometry of P(PhthMA-co-MMA)i» / „ depolymerization ( / Wn= 76.9 kg / mol) at 220 °C.

[0062] Fig. 55 illustrates the discrete ion mass tracking of various products observed during depolymerization of P(PhthMA-co-MMA)5%. An increase in ion peaks corresponding to MMA and CO2are observed after the onset of depolymerization.

[0063] Fig. 56 illustrates the thermogravimetric analysis displaying mass loss during the depolymerization of P(TCPhthMA-co-MMA)i% ( / Wr= 80.0 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0064] Fig. 57 illustrates the thermogravimetric analysis displaying mass loss during depolymerization of P(TCPhthMA-co-MMA)3% (Mn= 86.0 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0065] Fig. 58 illustrates the thermogravimetric analysis displaying mass loss during depolymerization of P(TCPhthMA-co-MMA)5% ( / Wr= 91 .0 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0066] Fig. 59 illustrates the thermogravimetric analysis displaying mass loss during depolymerization of P(SMA-co-MMA)i% (Mn= 70.1 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0067] Fig. 60 illustrates the thermogravimetric analysis displaying mass loss during depolymerization of P(SMA-co-MMA)3% (Mn= 69.3 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0068] Fig. 61 illustrates the thermogravimetric analysis displaying mass loss during depolymerization of P(SMA-co-MMA)5% (Mn= 82.6 kg / mol) at an isothermal hold at 290 °C for 2 h.

[0069] Fig. 62 illustrates the thermogravimetric analysis of P(SMA-co-MMA)i% (Mn= 70.1 kg / mol) at an isothermal hold at 180 °C for 2 h followed by depolymerization during an isothermal hold at 290 °C for 2 h.

[0070] Fig. 63 illustrates the thermogravimetric analysis of P(SMA-co-MMA)3%(Mn= 69.3 kg / mol) at an isothermal hold at 180 °C for 2 h followed by depolymerization during an isothermal hold at 290 °C for 2 h.

[0071] Fig. 64 illustrates the thermogravimetric analysis of P(SMA-co-MMA)5% (Mn= 82.6 kg / mol) at an isothermal hold at 180 °C for 2 h followed by depolymerization during an isothermal hold at 290 °C for 2 h.

[0072] Fig. 65 illustrates the thermogravimetric analysis during the depolymerization of P(PhthMA-co-MMA-co-EGDMA) network at an isothermal hold at 290 °C for 2 h.

[0073] Fig. 66 illustrates the thermogravimetric analysis during the depolymerization of P(PhthMA-co-MMA-co-EGDMA) network at an isothermal hold at 290 °C for 2 h.DETAILED DESCRIPTION

[0074] The present disclosure provides for polymers and modified polymers and methods of depolymerization of polymers and modified polymers. The present disclosure provides for an efficient approach for the depolymerization of polymers (e.g., poly(methyl methacrylate) (PMMA) copolymers) via pendent group activation. The present disclosure includes polymers that include a low mol% of thermolytically labile groups (e.g., phthalimide ester-containing monomers). Additional details are provided herein.

[0075] Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

[0076] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of thesesmaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

[0077] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described.

[0078] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

[0079] Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, material science, tribo- / rheology, and the like, which are within the skill of the art.

[0080] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions, methods, and materials disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C, and pressure is at or near atmospheric. Standard temperature and pressure are defined as 20 °C and 1 atmosphere.

[0081] Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible.

[0082] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0083] As used herein, the following terms have the meanings ascribed to them unless specified otherwise. In this disclosure, "consisting essentially of" or "consists essentially" or the like, when applied to methods and compositions encompassed by the present disclosure refers to compositions like those disclosed herein, but which may contain additional structural groups, composition components or method steps (or analogs or derivatives thereof as discussed above). Such additional structural groups, composition components or method steps, etc., however, do not materially affect the basic and novel characteristic(s) of the compositions or methods, compared to those of the corresponding compositions or methods disclosed herein. "Consisting essentially of or "consists essentially" or the like, when applied to methods and compositions encompassed by the present disclosure have the meaning ascribed in U.S. Patent law and the term is open-ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments.Definitions

[0084] By "chemically feasible" is meant a bonding arrangement or a compound where the generally understood rules of organic structure are not violated. The structures disclosed herein, in all of their embodiments are intended to include only "chemically feasible" structures, and any recited structures that are not chemically feasible, for example in a structure shown with variable atoms or groups, are not intended to be disclosed or claimed herein. However, if a bond appears to be intended and needs the removal of a group such as a hydrogen from a carbon, the one of skill would understand that a hydrogen could be removed to form the desired bond.

[0085] It is understood that “substitution” or “substituted” includes the implicit proviso that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound, i.e., a compound that does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, etc.

[0086] “Polymers” are understood to include, but are not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof.

[0087] As used herein, “alkyl” or “alkyl group” refers to a saturated aliphatic hydrocarbon, which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkyl groups include, but are not limited to methyl, ethyl,n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Reference to “alkyl” or “alkyl group” includes unsubstituted and substituted forms of the hydrocarbon moiety.

[0088] As used herein, “halo”, “halogen”, or “halide”, refers to a fluorine, chlorine, bromine, iodine, and astatine, and radicals thereof. Further, when used in compound words, such as “haloalkyl” refers to an alkyl or alkenyl radical in which one or more hydrogens are substituted by halogen radicals.

[0089] The term “unsaturated” refers to a molecule, such as a hydrocarbon or hydrocarbon moiety that includes one or more double bonds and / or triple bonds.

[0090] “Aryl”, as used herein, refers to C5-C2o-membered aromatic, heterocyclic, fused aromatic, fused heterocyclic, biaromatic, or bihetereocyclic ring systems. In an aspect, “aryl”, can include 5-, 6-, 7-, 8-, 9-, and 10-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, functional groups that correspond to benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine, and the like. Those aryl groups having heteroatoms in the ring structure may also be referred to as “aryl heterocycles” or “heteroaromatics”. The aromatic ring can be substituted at one or more ring positions with one or more substituents including, but not limited to, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino (or quaternized amino), nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromatic moieties, -CF3, -CN; and combinations thereof.

[0091] The term “aryl” also includes polycyclic ring systems (C5-C30) having two or more cyclic rings in which two or more carbons are common to two adjoining rings (i.e., “fused rings”) wherein at least one of the rings is aromatic, e.g., the other cyclic ring or rings can be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and / or heterocycles. Examples of heterocyclic rings include, but are not limited to, benzimidazolyl, benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl, benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aH carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl, decahydroquinolinyl, 2H,6H-1 ,5,2-dithiazinyl, dihydrofuro[2,3 b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl, isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1 ,2,3-oxadiazolyl, 1 ,2,4- oxadiazolyl, 1 ,2,5-oxadiazolyl, 1 ,3,4-oxadiazolyl, oxazolidinyl, oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenoxathinyl,phenoxazinyl, phthalazinyl, piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl, quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, tetrazolyl, 6H-1 ,2,5-thiadiazinyl, 1 ,2,3-thiadiazolyl, 1 ,2,4-thiadiazolyl, 1 ,2,5-thiadiazolyl, 1 ,3,4- thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl, 1 ,2,3-triazole, 1 ,2,4-triazole and xanthenyl. One or more of the rings can be substituted as defined above for “aryl”.

[0092] In some aspects, a structure of a compound can be represented by a formula:which is understood to be equivalent to a formula:where n is typically an integer. That is, Rnis understood to represent five independent substituents, Rn(a), Rn(b), Rn(c), Rn(d), and Rn(e). By “independent substituents,” it is meant that each R substituent can be independently defined. For example, if in one instance Rn<a> is halogen, then Rn<b> is not necessarily halogen in that instance.Discussion:

[0093] The present disclosure provides for polymers and modified polymers and methods of depolymerization of polymers and modified polymers. The present disclosure provides for an efficient approach for the depolymerization of polymers (e.g., poly(methyl methacrylate) (PMMA) copolymers) via pendent group activation. The present disclosure includes polymers that include a low mol% of thermolytically labile groups (e.g., phthalimide ester-containing monomers). The polymers can be synthesized via conventional radical polymerization to produce polymers that are colorless, transparent and closely resemble the unfunctionalized polymer. The method of depolymerization can achieve about 95% or more reversion to the monomer units (e.g., methyl methacrylate (MMA) if the functionalized polymer is PMMA). The depolymerization can be conducted catalyst-free and exhibits exceptional efficiency, even for high molecular weight polymers, including ultra-high molecular weight (106— 107g / mol) PMMA, for example, where near quantitative depolymerization is achieved. The method yields polymerbyproducts of significantly lower molecular weight, distinguishing it from bulk depolymerization methods initiated from chain ends.

[0094] In an aspect, the present disclosure provides for a composition that includes a polymer that includes thermolytically labile groups (Q). The thermolytically labile groups can includewhere each R1, R2, R3, R4, R5, R6, are R7can be independently selected from: H, an alkyl group (e.g., methyl, ethyl, propyl, butyl), halogen, -CN group, -O-alkyl (e.g., -OMe group), or an aryl group (the squiggly line indicates the bond to the polymer backbone). The molecular weight of the polymer can be about 1-10,000 kg / mol or about 100-10,000 kg / mol.

[0095] In an aspect, the polymer can have the following polymer backbone: following structure:, where x is about 0.25-25% (e.g., about 0.25 to 3.0%, about 1 .0 to 25.0%, or about 1 .0 to 3.0%), where y is about 75-99.75% (e.g., about 97- 99.75%, about 75 to 99%, or about 97 to 99%), and where m is 1 to 10,000. In the structure above, x is multiplied by m and y is multiplied by m. Q can be one of the thermolytically labile groups discussed above and herein, where the thermolytically labile group is bonded to a carbon of the polymer backbone. U can be a group that forms a monomer unit selected from: a methacrylate monomer, an acrylamide monomer, a methacrylamide monomer, an acrylate monomer, a styrenic monomer, a styrenic-derived monomer a vinyl pyridine monomer, a maleimide monomer, a maleic anhydride-derived monomer, a vinyl ester monomer, a vinyl amide monomer, a vinyl halide monomer, a substituted acrylamide, a substituted methacrylamide, or a derivative of anyone of these. In a particular aspect, the backbone unit can include a monomer unit or a copolymer including the monomer unit, where the monomer unit is selected from: alkyl methacrylates, acrylamide, A / ,A / -dimethylacrylamide, A / , / V-dialkylacrylamides, N- alkylacrylamides, A / ,A / -dialkyl methacrylamides, / V-alkyl methacrylamides, alkyl acrylates, oligo(ethylene glycol) acrylate, oligo(ethylene glycol) methacrylate, oligo(ethylene glycol)acrylamide, or oligo(ethylene glycol) methacrylamide, a substituted monomers units of each of these.

[0096] In an aspect, the polymer can be a copolymer with Q in a small amount relative to U. In an aspect, the monomer unit is a methacrylate monomer unit (e.g., methyl methacrylate monomer unit) or a styrenic monomer unit. In an aspect, the polymer is a copolymer (e.g., poly(A / -(methacryloxy)phthalimide-co-methyl methacrylate) (P(PhthMA-co-MMA). Each of R1and R2can be independently selected from: H, an alkyl group, halogen, -CN group, -O-alkyl (e.g., -OMe group), and aryl group. In particular, each of R1and R2can be independently selected from: a methyl group, an ethyl group, a propyl group, and a butyl group.

[0097] Figures 1-2, 4-6, 35-45, 50-52, and 56-66 illustrates various embodiments of polymers having the polymer backbone described above and herein as well as polymers including the thermolytically labile groups as described above and herein.

[0098] In an embodiment, the polymer can be linear or non-linear such as star-like, branched, hyperbranched, comb / brush-like, gradient copolymer, bottle brush-like, cyclic or network. A linear polymer can be defined as a macromolecular structure comprised of monomeric units covalently linked together in a sequential and unidirectional manner, forming a single continuous chain. This architecture is devoid of crosslinks, side chains and network structures that would arise from connections between polymer chains.

[0099] A branched polymer can be defined as a macromolecular architecture where one or more side chains extend from the primary linear backbone. For example, this architecture can result from the incorporation of monomers with multiple reactive sites during the polymerization process. These side chains, which may vary in length, regularity, and density create a more complex heterogeneous topology compared to linear polymers. The degree of branching (DB) can be calculated by the equation:where D represents molar equivalents of dendritic or branching unit, and L represents molar equivalents of the linear unit. Herein, branched polymers can be defined as having a DB greater than 0 but less than 0.4.

[0100] A hyperbranched polymer can be defined as a macromolecular structure characterized by tree-like topology that differentiates it from conventional branched polymers. The defining feature of hyperbranched polymers is their high DB, which is greater than 0.4 but less than 1 .

[0101] A star polymer can be defined as a macromolecular structure characterized by ‘arms’ extending from a central core. Star polymers have inherently more chain-ends thanlinear polymers. These ‘arms’, which may vary in length, regularity, and density create a more complex heterogeneous topology compared to linear polymers.

[0102] In an aspect, the backbone unit can include monomer units and copolymers including the monomer units. In an aspect, the polymer or modified polymer can be a block copolymer, a random copolymer, a statistical copolymer, an alternating copolymer, or a gradient copolymer.

[0103] A gradient copolymer is a polymer with more than one type of monomer unit where the frequency of occurrence of at least one monomer unit changes gradually along the polymer chain. A statistical copolymer is a copolymer in which the sequential distribution of the monomeric units obeys known statistical laws and is based on relative reactivities.

[0104] In another aspect, the present disclosure provides a method of depolymerization of polymer. The polymer can be a modified polymer that is modified to include a thermolytically labile group (Q) or a polymer that was originally prepared with a thermolytically labile group (Q). The unfunctionalized methacrylate polymer may be functionalized by transesterification with the compounds listed below to create the thermolytically labile group (Q). Additionally, the unfunctionalized polymer may be td above. The polymer or modified polymer to be depolymerized includes those described above in reference to the composition of the present disclosure and those described with the Examples section.

[0105] In an aspect, the method of depolymerization of a polymer (e.g., that includes the thermolytically labile groups (e.g., modified polymer)) includes heating the polymer to a temperature of about 180 to 300° C or 220 to 290° C for a time frame of about 0.1 to 24 h or about 10 to 180 min. After sufficient time, the polymer is depolymerized into the original monomer units. In an aspect, about 80% or more (e.g., about 80 to 99%) or about 90% or more (e.g., about 90 to 99%) of the monomer units can recovered. The method can be conducted in a catalyst-free environment (e.g., a catalyst is not added to the polymer during this method). It should be noted that a minor amount of a catalyst may be present in the polymer that is a residual amount from the method of making the polymer, but additional catalyst is not added to the polymer for the present depolymerization process. In an aspect, the monomer unit of the polymer can be themethacrylate monomer unit such as methyl methacrylate monomer unit (e.g., a poly(methyl methacrylate) polymer). Additional details are provided in Example 1.Example

[0106] While embodiments of the present disclosure are described in connection with the Examples and the corresponding text and figures, there is no intent to limit the disclosure to the embodiments in these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure.

[0107] In this study, we present an efficient approach for the depolymerization of poly(methyl methacrylate) (PMMA) copolymers synthesized via conventional radical polymerization. By incorporating low mol% phthalimide ester-containing monomers during the polymerization process, colorless and transparent polymers closely resembling unfunctionalized PMMA are obtained which can achieve >95% reversion to methyl methacrylate (MMA). Notably, our catalyst-free bulk depolymerization method exhibits exceptional efficiency, even for high molecular weight polymers, including ultra-high molecular weight (10s— 107g / mol) PMMA, where near quantitative depolymerization is achieved. Moreover, this approach yields polymer byproducts of significantly lower molecular weight, distinguishing it from depolymerization methods initiated from chain ends. Furthermore, we extend our investigation to polymethacrylate networks, demonstrating high extents of depolymerization. This innovative depolymerization strategy offers promising opportunities for the development of sustainable and high- performance polymethacrylate materials, holding great potential for various applications in polymer science.

[0108] The increase in demand of plastic materials has led to concomitant increase in plastic waste.1Despite the increased production of plastic materials, current recycling methods lag behind the rate at which the polymers are made.2Thus, polymer recycling has emerged as a pivotal area of research and innovation. Polymer recycling can be separated into two categories, thermomechanical recycling and chemical recycling.34Thermomechanical recycling often results in a reduction in the molecular weight and mechanical properties of the recycled polymer.56On the other hand, chemical recycling is a promising approach to convert polymer into monomer or its precursor forms. The recycled monomer can then be re-polymerized to afford new polymeric materials with identical or enhanced mechanical properties, providing an appealing approach to address the chemical circularity of polymers.7

[0109] While chemical recycling of some commercially relevant polymers such as polyethylene terephthalate) (PET) has been achieved through the nucleophilic attack of the ester backbone to yield monomer precursors,8-10degradation of vinyl-based polymers remains a formidable challenge due to their robust all-carbon backbones.11Efforts to impart degradability have centered around the incorporation of ester, thioester, and disulfide bonds within the polymer backbone.12-16Alternatively, the incorporation of monomers that can be triggered to generate main chain radicals allows efficient degradation of polymer backbones via p-scission.17-21However, many of these methods require catalysts or high dilution with solvent. For example, the inclusion of N- hydroxyphthalimide ester-containing monomers such as A / -(methacryloxy)phthalimide (PhthMA) can lead to direct main chain scission of polymethacrylates.21The PhthMA unit can accept an electron from a single electron donor which induces a cascade reaction, liberating CO2and generating a backbone radical which can cleave the polymer backbone via p-scission.21-25

[0110] Poly(methyl methacrylate) (PMMA) is a polymer with an all-carbon backbone produced via chain-growth polymerization. PMMA is a prominent and commercially significant polymer that is lightweight, colorless, and transparent.26PMMA is primarily used as glass substitutes in the aircraft and automotive industries but is also used in orthopedics and dentistry.2627The industrial production of PMMA currently resides at >4 million tons per year, with the production of PMMA expected to increase to nearly 6 million tons by 2027.28Industrially, PMMA is synthesized by conventional radical polymerization with molecular weights of 105— 10sg / mol. While PMMA can be recycled by thermomechanical methods, the material properties of the recycled PMMA are often compromised as the material is degraded to lower molecular weight. Alternatively, PMMA can be depolymerized to methyl methacrylate (MMA) by pyrolysis, with high temperatures used to induce C — C bond cleavage of the all-carbon backbone. The high temperatures used (>400 °C) induce random backbone cleavage and unzip the polymer chain, reverting polymer to monomer.29However, the high-temperature requirement results in a variety of undesired byproducts along with MMA.30

[0111] To circumvent the high temperatures needed to depolymerize PMMA, which also result in numerous impurities, recent work has centered around the depolymerization of PMMA synthesized by reversible-deactivation radical polymerization (RDRP) methods.31-35Initial work in this area demonstrated that the depolymerization of RDRP-derived polymethacrylates could be achieved efficiently in solution, with high dilutions being used to lower the ceiling temperature of the polymer.34Further work on the depolymerization of polymethacrylates derived from reversible addition-fragmentation chain transfer(RAFT) polymerization demonstrated that the depolymerization process could be accelerated when using light in tandem with heat to increase the rate of C — S bond cleavage.3637Concurrently, the Matyjaszewski group reported on a number of methods to depolymerize polymethacrylates synthesized by atom transfer radical polymerization (ATRP) at higher concentrations and temperatures.32 3335Anastasaki and coworkers have also demonstrated that the depolymerization of polymethacrylates can be achieved in a controlled manner by increasing the concentration of thiocarbonylthio moieties in solution to increase the rate of degenerative chain transfer and allow for the uniform depropagation of polymer chains.3839Although the aforementioned routes allow depolymerization of PMMA, the low concentration of polymer (~ 0.05 wt%) means that these methods may be difficult to apply on an industrial scale.

[0112] To increase the commercial viability of depolymerizing PMMA, bulk depolymerization methodologies of RDRP-made PMMA have recently been reported. The inclusion of labile chain-ends such as halogens, thiocarbonlythio, and A / -hydroxyphthalimide esters have allowed for high extents of depolymerization at significantly lower temperatures than industrially used, affording highly pure MMA for new materials. Anastasaki and coworkers demonstrated that the depolymerization of PMMA synthesized by RAFT polymerization and ATRP could be depolymerized with high efficiencies in a two-step catalytic process.40Matyjaszewski and coworkers also reported on the rapid depolymerization of PMMA synthesized by ATRP by using a copper halide catalyst which activated the carbon-halogen polymer chain-end to generate a PMMA macroradical which was then depolymerized.41We reported the bulk depolymerization of PMMA in a one-step, catalyst-free approach, achieved through the thermolysis of labile a- and co - chain-ends which afforded high extents of depolymerization to MMA.42In the previous report, chain-ends inherent to ATRP and RAFT polymerization were investigated, with the highest extents of depolymerization (>90%) achieved with polymers containing a / V- hydroxyphthalimide ester on the a-end and a trithiocarbonate on the co-end. By analyzing the thermogravimetric analysis (TGA) data, we attributed 60% depolymerization to initiation from the a-end / V-hydroxyphthalimide ester and 30% depolymerization from the w-end trithiocarbonate.

[0113] Despite the current reports on the depolymerization of PMMA providing great advances in the field, the approaches are reliant on RDRP methods to allow for efficient depolymerization through their thermolytically labile chain-ends. As a result, the polymers are often colored or require catalysts for efficient depolymerization in the bulk. In addition, low extents of depolymerization are achieved at high molecular weights, which is problematic given that high molecular weight PMMA is commercially important.42 43Tofurther improve the recyclability of PMMA, new depolymerization methodologies that address the drawbacks inherent to depolymerizable PMMA synthesized by RDRP, which may prevent adoption by industry, are required.44Herein, we demonstrate a route to synthesize depolymerizable PMMA by conventional radical polymerization. The incorporation of low-mol% PhthMA generates backbone radicals at elevated temperatures and affords high extents of depolymerization to generate MMA. This depolymerization methodology is efficient across a broad array of polymer molecular weights with up to 95% depolymerization achievable for higher molecular weight polymers at significantly lower temperatures than those industrially used.

[0114] Results and Discussion

[0115] Poly( / V-(methacryloxy)phthalimide-co-methyl methacrylate) (P(PhthMA-co-MMA)) copolymers were synthesized by conventional radical polymerization at 70 °C in dimethylsulfoxide (DMSO), employing azobisisobutyronitrile (AIBN) as the initiator. The PMMA copolymers were synthesized with varying molar ratios of PhthMA to investigate the effect of different amounts of the radical trigger on the extent of depolymerization (Figure 12-17). The molar ratios of PhthMA were determined by the integrations of the aromatic protons relative to the methyl ester protons of PMMA by1H NMR spectroscopy (Figure 35-37). The polymers ranged in molecular weight between 60-80 kg / mol. The TGA traces of the PMMA copolymers showed significant mass loss beginning at 180- 200 °C upon heating to 500 °C at a heating rate of 5 °C / min. The T95 of the polymers differed based on the incorporation of PhthMA, with higher incorporations resulting in lower T95 values. The highest T95of 234 °C was observed for the P(PhthMA-co-MMA)i% and the lowest T95of 185 °C for P(PhthMA-co-MMA)5% (Figure 1 B).

[0116] Averaging the T95of the P(PhthMA-co-MMA) copolymers containing 1 , 3 and 5 mol% PhthMA resulted in an averaged T95of 205 °C, roughly 170 °C lower than PMMA homopolymers synthesized via anionic or conventional radical polymerization methods.30The inclusion of higher molar ratios of PhthMA resulted in higher mass loss by TGA, with up to 98% mass loss achievable for P(PhthMA-co-MMA)5%. To determine the extent of depolymerization of PMMA from TGA, we subtracted the wt% of PhthMA from the total mass loss observed. Gratifyingly, we observe very high extents of depolymerization (~90%) for all the P(PhthMA-co-MMA) copolymers, with as little as 1% incorporation of PhthMA achieving ~90% depolymerization (Figure 1A-1C).

[0117] To provide evidence that the mass loss observed by TGA was a result of depolymerization, TGA-tandem mass spectrometry (TGA-MS) was used. At room temperature, no peaks that correspond to monomer were observed; however, afterincreasing the temperature to 220 °C, molecular ion signals for MMAwere present (Figure 53, 54). To provide insight into the mechanism of depolymerization, select ion fragments were tracked over time. The ion peak corresponding to CO2increased after the onset of depolymerization, leading us to believe that depolymerization first proceeds via N— O bond cleavage of the A / -hydroxyphthalimide ester and decarboxylation of the carboxylate radical to generate a backbone radical (Figure 55). The ion peaks that correspond to MMA also increased after the onset of depolymerization; as such we attribute the observed reduction in polymer mass primarily to depolymerization following P-scission of the backbone radical (Figure 55).

[0118] Inspired by the result that pendent group A / -hydroxyphthalimide esters could efficiently trigger the depolymerization of PMMA at elevated temperatures, we sought to tune the onset of depolymerization by changing the ester that acts as the radical trigger. / V- (Methacryloxy)tetrachlorophthalimide (TCPhthMA) was synthesized with the idea that it would result in faster thermolysis and a decrease in the onset temperature of depolymerization due to a weaker N — O bond strength (Figure 7-10). Varying ratios of TCPhthMA were copolymerized with MMA by conventional radical polymerization to produce P(TCPhthMA-co-MMA) copolymers. The incorporation of TCPhthMA was estimated from the feed ratio of TCPhthMA to MMA due to the absence of distinguishing 1H NMR signals in the resulting copolymer. After purification, the synthesized copolymers of varying composition were of similar molecular weight, ranging from 60-80 kg / mol (Figure 18-23). Gratifyingly, the T95 for the P(TCPhthMA-co-MMA)i% was reduced by 40 °C to 194 °C compared to the P(PhthMA-co-MMA)i%. The averaged T95 values were reduced to 190 °C for the P(TCPhthMA-co-MMA) copolymers, demonstrating that it is possible to successfully tune the onset temperature of depolymerization. The TGA profiles of these copolymers exhibited a consistent pattern, with higher levels of TCPhthMA correlating with increased mass loss during depolymerization (Figure 2C). High extents of depolymerization were also achieved for these copolymers (~80%) (Figure 56-58).

[0119] Given that it was possible to decrease the onset temperature of depolymerization by the addition of the chlorine atoms to the aromatic ring of the A / -hydroxyphthalimide ester, we then aimed to also increase the onset temperature of depolymerization. Increasing the onset temperature for depolymerization may be an important consideration, given that PMMA is typically processed at temperatures ranging from 180-220 °C. We hypothesized that by removing the aromatic ring of the / V-hydroxyphthalimide ester, the bond strength of the N — O bond would increase and result in higher temperatures required for depolymerization. / \ / -(Methacryloxy)succinimide (SMA) (Figure 11) wascopolymerized with MMAto produce P(SMA-co-MMA) copolymers, using the aforementioned conditions with 1 , 3, or 5 mol% SMA (Figure 24-29). The incorporations of SMA were determined by1H NMR spectroscopy by comparing the methylene protons of SMA to those of the methyl ester of PMMA (Figure 38-40). Gratifyingly the averaged T95 of the P(SMA-co-MMA) copolymers was increased to 232 °C, nearly 30 °C higher than that of the P(PhthMA-co-MMA) copolymers (Figure 2D). The extents of depolymerization were also high for the P(SMA-co-MMA) copolymers with up to 85% depolymerization achievable (Figure 59-61). Inspired by our result in increasing the T95, we sought to investigate whether the P(SMA-co-MMA) copolymers were amenable to heating at 180 °C without inducing depolymerization. To investigate the thermal stability of the P(SMA-co-MMA) copolymers, the copolymers were subjected to an isothermal hold at 180 °C for 2 h by TGA. The TGA traces of all P(SMA-co-MMA) copolymers showed no mass loss over the 2 h period, while a sequential isothermal hold at 290 °C demonstrated significant mass loss, up to 95% for the P(SMA-co-MMA)5% copolymer which equates to 85% depolymerization (Figure 62-64). These results suggest that the P(SMA-co-MMA) copolymers may be amenable to current industrial PMMA processing conditions, which is attractive to ensure PMMA can be depolymerized intentionally and on command at elevated temperatures, and not during processing.

[0120] Previous reports on the depolymerization of PMMA using labile chain ends both under dilute and bulk conditions have demonstrated a depolymerization dependence on molecular weight.42 43The previously mentioned strategies result in high extents of depolymerization of low molecular weight PMMA but a significant reduction in the extent of depolymerization for higher molecular weight polymers. Inspired by our results of achieving high extents of depolymerization for the P(PhthMA-co-MMA) copolymers, with molecular weights ~70 kg / mol, we sought to investigate the depolymerization dependence on molecular weight when depolymerization is initiated from the pendent group. To investigate this, P(PhthMA-co-MMA)i% of varying molecular weights were synthesized by conventional radical polymerization by tuning the amount of radical initiator (Figure 30-34, 41-45). UHMW copolymers45-51were synthesized by using very low concentrations of radical initiator to monomer. The synthesized copolymers were subjected to TGA in which an isothermal hold at 290 °C for 2 h was used to determine the mass loss, and the extent of depolymerization determined after accounting for the wt% of PhthMA within the polymer. High extents of depolymerization were observed for all polymers (>80%) (Figure 3). Interestingly, higher molecular weight samples reached greater extents of depolymerization. The depolymerization of high and UHMW polymers yielded >95% depolymerization, which is a 50% increase over chain end-initiateddepolymerization methodologies of polymers of similar molecular weight.42We believe the greater extent of depolymerization of higher molecular weight polymers is owed to the greater number of PhthMA units per chain — which results in a greater fraction of the polymer chain that can be depolymerized (Figure 3).

[0121] Given that PMMA is often employed in applications that require colorless materials with high optical clarity, we investigated the optical properties of the depolymerizable copolymers by UV-Vis spectroscopy (Figure 4A, 4C, 4E). Solutions of the P(PhthMA-co- MMA) and P(TCPhthMA-co-MMA) copolymers demonstrated no absorbance at wavelengths within the visible range and only absorbance between 250-365 nm attributable to the TT-TT* transitions of the aromatic rings, while a slight absorbance was also observed at 425 nm for the P(TCPhthMA-co-MMA) copolymer. The P(SMA-co- MMA) copolymer demonstrated no absorbance between 200-600 nm. Thin films of P(PhthMA-co-MMA)i%, P(TCPhthMA-co-MMA)i%, and P(SMA-co-MMA)i% were created by dissolving the polymers in dichloromethane to prepare 10 wt% polymer solutions. The solutions were solvent cast and allowed to evaporate. The images in Figure 4 demonstrate the high transparency and colorless nature of the synthesized polymers. Both the P(PhthMA-co-MMA)i" / 0and the P(SMA-co-MMA)i% thin films are colorless like that of unfunctionalized PMMA (Figure 4B, 4F). From a top-down view of P(TCPhthMA- co-MMA)i% the polymer appears both colorless and transparent (Figure 4D); however, from a side-on view of the thin film, a slight green color is observed, which is likely a result of the absorbance of the copolymer at 425 nm (Figure 46B). These results provide promise for these polymer materials to be used as optical materials.

[0122] We aimed to demonstrate that MMA could be recovered from the bulk depolymerization and simultaneous distillation of the copolymers (Figure 5A). Solid P(PhthMA-co-MMA)i% was added to a round bottom flask equipped with a distillation apparatus, and the polymer was heated to 250 °C in a sand bath under vacuum (Figure 47A). After depolymerization, a colorless liquid was obtained in the collection flask (Figure 47B). The 1H NMR spectrum of the colorless liquid confirmed its identity as MMA with no discernable byproducts observed (Figure 5B). This depolymerization methodology afforded 81% recovery of the theoretical mass of MMA.

[0123] The recovered MMA was used for polymerization to synthesize P(PhthMA-co-MMA)i%, demonstrating the potential chemical circularity of this depolymerization methodology (Figure 48). After reaction completion, a small amount of brown solid was left in the initial round-bottom flask. To determine the identity of the material, the byproduct was analyzed by size-exclusion chromatography (SEC) and1H NMR spectroscopy. Given our hypothesis that p-scission of the polymer backbone precedes depolymerization, lowmolecular weight polymer byproducts are expected. The SEC trace of the residual solid indicated polymer of low number-average molecular weight (Mn= 8.02 kg / mol), which supports our hypothesis that depolymerization is initiated via the pendent group via p- scission of the polymer backbone (Figure 5C). The1H NMR spectrum of the polymer byproduct demonstrated peaks that correspond to PMMA. Alkenyl proton peaks were observed between 47-4.9 ppm, which are consistent with depolymerization being initiated after p-scission (Figure 49).21 52

[0124] To further demonstrate the versatility of the pendent-group approach, depolymerization of polymer networks were explored. This is potentially important since crosslinked polymers are typically more difficult to recycle than thermoplastics. Polymethacrylate networks were synthesized from the copolymerization of MMA (85 or 90%), PhthMA (5 mol%), and ethylene glycol dimethacrylate (EGDMA, 5 or 10 mol%). Depolymerization of the polymethacrylate networks reached high extents of mass loss (>95%) when subjected to an isothermal hold at 290 °C for 2 h (Figure 65, 66). The extent of mass loss was independent of the amount of EGDMA added. Given that EDGMA is a dimethacrylate crosslinker, the independence of the incorporation of EGDMA on the mass loss can be rationalized by depolymerization occurring across both ends of the dimethacrylate crosslinker. This result is promising since the recycling of thermoset polymers is limited.

[0125] In conclusion, we have demonstrated an efficient method to prepare depolymerizable PMMA by conventional radical polymerization. The incorporation of / V-hydroxy phthalimide / succinimide ester pendent groups, which are thermolytically labile, allows for high extents of depolymerization in the absence of catalysts to generate highly pure MMA. This depolymerization methodology is efficient across a broad range of molecular weights, with near-quantitative reversion to monomer even at UHMW. The T95of the polymers is tunable by modulation of the comonomer incorporation. P(SMA-co-MMA) copolymers were thermally stable at 180 °C for 2 h, which is important given that PMMA is often thermally (re)processed at this temperature. Bulk PMMA networks were also able to achieve high extents of depolymerization, setting a precedent for new methods of bulk thermoset recyclability. This approach provides a more facilitated route to chemically recyclable PMMA and does not rely on synthesis by controlled / living polymerization techniques. REFERENCES

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[0178] Example 2: Supporting Information for Example 1

[0179] Materials and Instrumentation

[0180] Materials:

[0181] All chemicals were used as received unless otherwise noted. Methyl methacrylate (MMA, Sigma-Aldrich, 99%) was passed through a plug of basic alumina to remove inhibitor immediately prior to use. Dichloromethane (DCM), A / , / V-dimethylformamide (DMF, ACS Grade), methanol, hexanes, chloroform, and anhydrous magnesium sulfate were purchased from Fisher Scientific. Ethanol (200 proof) was purchased from Decon Laboratories. Tetrachlorophthalic anhydride, triethylamine, methacryloyl chloride, N- hydroxysuccinimide, and hydroxylamine hydrochloride were purchased from Sigma- Aldrich. Azobisisobutyronitrile (AIBN, Millipore Sigma, 98%) was recrystallized from methanol and dried in vacuo prior to use. Deuterated chloroform (CDCI3, 99.8% with 0.05% v / v TMS) and deuterated methanol (CD3OD, 99.8%) were purchased from Cambridge Isotope Laboratories, Inc.

[0182] Instrumentation:

[0183] NMR Spectroscopy.1H NMR spectroscopy was recorded using an Inova 500 MHz 2 RF channel spectrometer. Monomer conversion was tracked by1H NMR spectroscopy with a Magritek Spinsolve Ultra 60 mHz benchtop spectrometer with the olefin protons referenced to DMF.1H NMR chemical shifts in CDCI3were referenced to CHCI3(7.26 ppm).

[0184] Size-Exclusion Chromatography (SEC). Size-exclusion chromatography (SEC) was performed in A / , / V-dimethylacetamide (DMAc) with 50 mM LiCI at 50 °C at a flow rate of 1.0 mL / min (Agilent isocratic pump, degasser, and autosampler; columns: Viscogel I- series 5 pm guard + two ViscoGel l-series G3078 mixed bed columns, molecular weight l ' lrange 0-20,000 g / mol and 0-1 ,000,000 g / mol). Detection consisted of a Wyatt Optilab T- rEX refractive index detector operating at 658 nm and a Wyatt miniDAWN Treos light scattering detector operating at 690 nm. Absolute molecular weights and molecular weight distributions were calculated using the Wyatt ASTRA software, and dn / dc values were obtained from 100% mass-recovery methods.

[0185] Thermogravimetric Analysis (TGA). TGA experiments were collected on a TA 5500 equipped with an autosampler using a 100 pL platinum pan. Each sample was run after precipitation and vigorous drying under vacuum. Ramp experiments were heated at 10 °C / min from room temperature to 500 °C under nitrogen flow (25 mL / min). All low- temperature TGA experiments were recorded using TAs Thermal Advantage for Q Series software.

[0186] Tandem Mass Spectrometry. A TA 5500 series TGA was equipped with an MKS DMS Series II mass spectrometer to analyze ion fragments from polymer samples. The instrument utilizes a 1-300 amu quadrupole mass filter with a closed ion source. Bar chart experiments were used to scan all ion fragments from polymer samples with peak jump mode used to detect discrete ions for tracking the generation of identifiable ions. All data were processed using ProcessEye software and exported as a text file to Origin.

[0187] Ultraviolet-visible spectrometer (UV-vis). UV-vis absorbance spectra were recorded on the Molecular Devices SpectraMax M2 multimode microplate reader. Stock solutions of the PMMA copolymers were created in DMSO at a concentration of 5 mg / mL.Samples were prepared by diluting 50 pL of the polymer stock solution with DMSO (150 pL) in a clear polypropylene 96-well plate.

[0188] Monomer Synthesis

[0189] A / -(methacryloxy)phthalimide (PhthMA)

[0190] / V-Hydroxyphthalimide (19.6 g, 120 mmol) and chloroform (170 mL) were added to a1000 mL round bottom flask (RBF) along with a stir bar. To the RBF on ice, triethylamine (18.2 mL, 130 mmol) was added dropwise. Following the addition of triethylamine,methacryloyl chloride (12.9 mL, 132 mmol) was added dropwise to the RBF on ice. The reaction was allowed to warm to room temperature with stirring overnight. The reaction solution was washed with water (100 mL x 4) and brine (100 mL x 1). The organic phase was dried over anhydrous magnesium sulfate before removing the solvent under reduced pressure. The crude product was purified by recrystallization from methanol. Yield = 50%.

[0191] / V-hydroxytetrachlorophthalimide

[0192] To 250 mL RBF equipped with a stir bar, NH2OH HCI (11.9 g, 171 mmol), triethylamine (17.1 g, 23.6 mL, 169 mmol) and ethanol (700 mL) were added. The reaction mixture was stirred for 10 min, prior to the addition of tetrachlorophthalic anhydride (25.0 g, 87.4 mmol). The reaction mixture was refluxed for 16 h. The reaction mixture was condensed to yield a red precipitate. The red precipitate was rinsed with minimal amount of sulfuric acid to generate a yellow precipitate. The yellow precipitate was washed with DI water and collected via vacuum filtration. The yellow precipitate was dissolved in ethanol (80 mL), and the product precipitated by the addition of ice-cold water. The precipitated product was collected via vacuum filtration and purified by recrystallization in ethanol to yield pure / V-hydroxytetrachlorophthalimide. Yield = 45%.

[0193] / V-(methacryloxy)tetrachlorophthalimide (TCPhthMA)

[0194] To a 100 mL RBF on ice equipped with a stir bar, / V-hydroxytetrachlorophthalimide (11.8 g, 39.2 mmol) and chloroform (58.8 mL) were added. Triethylamine (5.94 mL, 42.6 mmol) was added dropwise to the RBF. Methacryloyl chloride (4.50 mL, 77.3 mmol) wasadded dropwise to the RBF on ice for 30 min. The reaction was allowed to warm to room temperature with stirring over 16 h. The resulting reaction mixture was washed with water (16 mL x 4) and brine (16 ml_ x 1) before drying over anhydrous MgSO4. The resulting mixture was condensed to yield a yellow crude precipitate. The yellow precipitate was dissolved in minimal amount of DCM and gravity filtered to separate the insoluble by-product. The dissolved product was purified by column chromatography (70:30, DCM:hexanes). Yield = 21%.

[0195] / \ / -(methacryloxy)succinimide (SMA)

[0196] To a 100 mL RBF on ice / V-hydroxysuccinimide (6.00 g, 52.1 mmol) was added along with chloroform (60 mL) and a stir bar. Triethylamine (7.92 mL, 56.8 mmol) was added dropwise with stirring to the RBF Methacryloyl chloride (5.58 mL, 57.4 mmol) was added dropwise to the RBF with stirring over the course of 30 min. The reaction was allowed to warm to room temperature and stirred overnight. The reaction solution was washed with DI water (3 x 100 mL) and brine (1 x 100 mL) before drying the organic phase over anhydrous magnesium sulfate. The solvent was removed on a rotary evaporator, leaving a white-brown solid. The crude product was recrystallized from methanol three times leaving a white-crystalline solid. Yield = 31%.

[0197] Polymer Synthesis

[0198] General Synthesis of P(PhthMA-co-MMA)

[0199] To a 10 mL Schlenk flask, MMA (1.93 mL, 18.1 mmol), PhthMA (0.04 g, 0.183 mmol), AIBN (15.0 mg, 0.0910 mmol), DMSO (7.21 mL), and DMF (0.700 mL) were added along with a stir bar. The reaction solution was sparged with argon for 30 min prior to heating the reaction at 70 °C until high conversion was reached, which was monitored by1H NMR. The polymer was purified by precipitation into cold methanol. The purified polymer was analyzed by1H NMR spectroscopy and SEC.

[0200] General Synthesis of P(TCPhthMA-co-MMA)

[0201] To a 25 mL Schlenk flask MMA (4.82 mL, 45.2 mmol), TCPhthMA (0.169 g, 0.457 mmol), AIBN (37.0 mg, 0.225 mmol), DMSO (16.3 mL), and DMF (1.70 mL) were added along with a stir bar. The reaction solution was sparged with argon for 30 min prior to heatingthe reaction at 70 °C until high conversion was reached which was monitored by1H NMR. The polymer was purified by precipitation into cold methanol. The purified polymer was analyzed by1H NMR spectroscopy and SEC.

[0202] Synthesis of P(SMA-co-MMA)

[0203] To a 25 mL Schlenk flask MMA (3.86 mL, 36.2 mmol), SMA (0.0700 g, 0.366 mmol), AIBN (30.0 mg, 0.182 mmol), DMSO (14.4 mL), and DMF (1.40 mL) were added along with a stir bar. The reaction solution was sparged with argon for 30 min prior to heating the reaction at 70 °C until high conversion was reached which was monitored by1H NMR. The polymer was purified by precipitation into cold methanol. The purified polymer was analyzed by1H NMR spectroscopy and SEC.

[0204] General Synthesis of P(PhthMA-co-MMA-co-EGDMA) Networks

[0205] To a 10 mL Schlenk flask MMA (0.969 mL, 9.00 mmol), PhthMA (0.116 g, 0.500 mmol), EGDMA (0.0950 mL, 0.500 mmol), and AIBN (0.640 mg, 0.0100 mmol), and dioxane (0.600 mL) were added along with a stir bar. The reaction solution was sparged with argon for 30 min prior to heating the reaction at 70 °C for 24 h. The network was crushed to a fine powder and dried under vacuum at 100 °C. The purified polymer network was analyzed by TGA.

[0206] Polymer Thin Films

[0207] The PMMA copolymers (0.700 g) were added to separate scintillation vials and dissolved in DCM (7.00 g). The dissolved polymers were transferred to separate petri dishes and allowed to evaporate at room temperature.

[0208] Example Bulk Distillation Procedure

[0209] To a 25 mL RBF, P(PhthMA-co-MMA)i% (0.500 g of 76.9 kg / mol) was added, and the flask was equipped with a condenser and a collection tube. The RBF was lowered into a preheated sand bath (250 °C), and vacuum was applied to the distillation setup as needed to collect monomer. After approximately 2.5 h, the condensation of MMA was no longer observed, and monomer was collected (0.390 mL, 81.0% yield) with high purity, as evidenced by the1H NMR spectrum (Figure 5D). The residual byproduct was collected and analyzed by1H NMR spectroscopy and SEC (Figure 5E, 46).

[0210] It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 25%” should be interpreted to include notonly the explicitly recited concentration of about 0.1 mol% to about 25 mol%, but also include individual concentrations (e.g., 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%, 5.5%, 10.1%, 15.5%, 20.2%) within the indicated range. In an embodiment, “about O’’ can refer to 0, 0.001 , 0.01 , or 0.1. In an embodiment, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about x’ to about ‘y’”.

[0211] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.

Claims

Claims1. A composition comprising: a polymer having the following structure:, wherein x is about 0.25-25%, wherein y is about 75-99.75%, wherein m is 1 to 10,000, wherein each of R1and R2are independently selected from H, an alkyl group, halogen, a -CN group, a -O-alkyl group, an aryl group, wherein U is a group that forms a monomer unit selected from: a methacrylate monomer, an acrylamide monomer, a methacrylamide monomer, an acrylate monomer, a styrenic monomer, a styrenic-derivative monomer, a vinyl pyridine monomer, a maleimide monomer, a maleic anhydride-derived monomer, a vinyl ester monomer, a vinyl amide monomer, a vinyl halide monomer, a substituted acrylamide, a substituted methacrylamide, or a derivative of anyone of these,halogen, a -CN group, an -O-alkyl group, and an aryl group (the squiggly line indicates the bond to the polymer backbone).

2. The composition of claim 1 , wherein the monomer unit is the methacrylate monomer unit.

3. The composition of claim 2, wherein the methacrylate monomer unit is a methyl methacrylate monomer unit.

4. The composition of claim 1 , wherein the monomer unit is the styrenic monomer unit.

5. The composition of claims 1 to 4, wherein the polymer is a copolymer.

6. The composition of claims 1 to 4, wherein x is 0.25-25%, wherein y is about 75-99.75%.

7. A method of depolymerization a polymer comprising one or more of the following pendent groups:wherein each R1, R2, R3, R4, R5, R6, and R7are independently selected from H, an alkyl group, halogen, a -CN group, an -O-alkyl group, and an aryl group (the squiggly line indicates the bond to the polymer backbone), heating the polymer to about 180 to 300° C, wherein the polymer is a polymer as described in one of claims 1-6; and depolymerization of the polymer, wherein about 90% of the monomer units are recovered.8 The method of claim 7, wherein a molecular weight of the polymer is about 1-10,000 kg / mol.

9. The method of claims 7 and 8, wherein the polymer is a copolymer, wherein the copolymer includes a monomer unit selected from: a methacrylate monomer, an acrylamide monomer, a methacrylamide monomer, an acrylate monomer, a styrenic monomer, a vinyl pyridine monomer, a maleimide monomer, a maleic anhydride-derived monomer, a vinyl ester monomer, a vinyl amide monomer, a vinyl halide monomer, a substituted acrylamide, a substituted methacrylamide, or a derivative of anyone of these.

10. The method of claim 9, wherein the monomer unit is the methacrylate monomer unit.11 . The method of claim 10, wherein the methacrylate monomer unit is a methyl methacrylate monomer unit.

12. The method of claim 9, wherein the monomer unit is a styrenic monomer unit.

13. The method of claims 7 to 9, wherein the heating comprising heating the polymer to about 180 to 290° C.

14. The method of claims 7 to 9, wherein the method is performed in a catalyst-free environment, a solvent-free environment, or both a catalyst-free environment and a solvent- free environment.

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