An efficient process for the depolymerization of vinyl polymers

Abstract

The present invention relates to a highly efficient process for the photo-initiated depolymerization of vinyl polymers in the presence of at least one chlorine-containing reagent, preferably at elevated temperatures. The invention further relates to the recycling of vinyl polymers comprising the process according to the invention as well as the use of chlorine-containing reagents for the depolymerization of vinyl polymers.

Description

[0001] An efficient process for the depolymerization of vinyl polymers

[0002] Field of the Invention

[0003] The present invention relates to a highly efficient process for the photo-initiated depolymerization of vinyl polymers in the presence of at least one chlorine-containing reagent, preferably at elevated temperatures. The invention further relates to the recycling of vinyl polymers comprising the process according to the invention as well as the use of chlorine-containing reagents for the depolymerization of vinyl polymers.

[0004] Background

[0005] Plastics have long since become an indispensable class of materials, replacing traditional materials such as glass, leather, ceramics, and metals. Their extensive use and durability, however, has led to environmental concerns ranging from greenhouse gas emissions to microplastic contamination of marine life. Addressing these challenges necessitates a transition to a circular economy through recycling. Unfortunately, the predominant method, thermomechanical recycling, results in the downcycling into lower-grade products via reduction in the molecular weight. To circumvent product deterioration, alternatives such as “upcycling” (see [1] S. Oh, E. E. Stache, Chemical Upcycling of Commercial Polystyrene via Catalyst-Controlled Photooxidation. J. Am. Chem. Soc. 144, 5745-5749 (2022) and [2] C. Jehanno et al.. Critical advances and future opportunities in upcycling commodity polymers. Nature 603, 803-814 (2022)) and chemical recycling to monomer (see [1], [3] A. Abel, R. L. Snyder, G. W. Coates, Chemically recyclable thermoplastics from reversible -deactivation polymerization of cyclic acetals, Science 373, 783-789 (2021) and [4] T. M. McGuire, A. Buchard, C. Williams, Chemical Recycling of Commercial Poly(l-lactic acid) to 1-Lactide Using a High- Performance Sn(II) / Alcohol Catalyst System, J. Am. Chem. Soc. 145, 19840-19848 (2023)) have been explored. The latter is particularly appealing as it not only establishes the smallest closed-loop cycle, but also opens up the option to synthesize completely different polymeric materials (see [1]).

[0006] A major challenge is the deconstruction of vinyl polymers with all -carbon backbones due to the absence of heteroatom-associated weak links, the very trait that imparts chemical stability to these materials e.g. from hydrolysis.

[0007] Poly(methyl methacrylate) (PMMA) is a vinyl polymer widely used as a glass substitute in a variety of applications, notably as protective barriers during the COVID- 19 pandemic. Pyrolysis of PMMA requires temperatures exceeding 400 °C but this process generates undesirable byproducts such as 2,3-butanedione, a compound that imparts a pungent odor to the recycled PMMA (see [5] C. B. Godiya et al., Depolymerization of waste poly(methyl methacrylate) scraps and purification of depolymerized products, Journal of Environmental Management 231, 1012-1020 (2019)). Recent advances in controlled radical polymerization (CRP) (see [6] G. Moad, in Macromolecular Engineering, pp. 1-61, [7] P. Krys, K. Matyjaszewski, Kinetics of Atom Transfer Radical Polymerization, Eur. Polym. J. 89, 482-523 (2017), [8] K. Parkatzidis, H. S. Wang, N. P. Truong, A. Anastasaki, Recent developments and future challenges in controlled radical polymerization: A 2020 update, Chem. 6, 1575-1588 (2020), [9] D. T. Gentekos, R. J. Sifri, B. P. Fors, Controlling polymer properties through the shape ofthe molecular-weight distribution, Nat. Rev. Mater. 4, 761-774 (2019) and

[0010] C. Boyer et al., Bioapplications of RAFT Polymerization, Chem. Rev. 109, 5402-5436 (2009)) have enabled the reduction of reaction temperatures, leveraging pre-installed labile chainends to facilitate depolymerization at lower temperatures (100-170°C) (see

[0011] M. R. Martinez, K. Matyjaszewski, Degradable and Recyclable Polymers by Reversible Deactivation Radical Polymerization, CCS Chem. 4, 1-36 (2022);

[0012] M. R. Martinez, F. De Luca Bossa, M. Olszewski, K. Matyjaszewski, Copper (II) Chloride / Tris (2-pyridylmethyl) amine-Catalyzed Depolymerization of Poly (n-butyl methacrylate), Afocromo / ecules, (2021),

[0013] M. R. Martinez, S. Dadashi-Silab, F. Lorandi, Y. Zhao, K. Matyjaszewski, Depolymerization of P(PDMS1 IMA) Bottlebrushes via Atom Transfer Radical Polymerization with Activator Regeneration, Afocromo / ecules 54, 5526-5538 (2021),

[0014] M. R. Martinez, D. Schild, F. De Luca Bossa, K. Matyjaszewski, Depolymerization of Polymethacrylates by Iron ATRP, Afocromo / ecules 55, 10590-10599 (2022),

[0015] F. De Luca Bossa, G. Yilmaz, K. Matyjaszewski, Fast Bulk Depolymerization of Polymethacrylates by ATRP, ACS Macro Lett. 12, 1173-1178 (2023),

[0016] K. Parkatzidis, N. P. Truong, K. Matyjaszewski, A. Anastasaki, Photocatalytic ATRP Depolymerization: Temporal Control at Low ppm of Catalyst Concentration, J. Am. Chem. Soc. 145, 21146-21151 (2023),

[0017] H. S. Wang, K. Parkatzidis, T. Junkers, N. P. Truong, A. Anastasaki, Controlled radical depolymerization: Structural differentiation and molecular weight control, Chem. 10, 1-14 (2023),

[0018] F. Hafliger, N. P. Truong, H. S. Wang, A. Anastasaki, Fate of the RAFT End-Group in the Thermal Depolymerization of Polymethacrylates. , CS Macro Lett. 12, 1207-1212 (2023),

[0019] H. S. Wang, N. P. Truong, G. R. Jones, A. Anastasaki, Investigating the Effect of End-Group, Molecular Weight, and Solvents on the Catalyst-Free Depolymerization of RAFT Polymers: Possibility to Reverse the Polymerization of Heat-Sensitive Polymers, ACS Macro Lett. 11, 1212-1216 (2022),

[0020] V. Mellott i et al., Light- accelerated depolymerization catalyzed by Eosin Y, Polym. Chem. 14, 253-258 (2023),

[0021] H. S. Wang, N. P. Truong, Z. Pei, M. L. Coote, A. Anastasaki, Reversing RAFT Polymerization: Near- Quantitative Monomer Generation Via a Catalyst-Free Depolymerization Approach., J. Am. Chem. Soc. 144, 4678-4684 (2022),

[0022] V. Bellotti, H. S. Wang, N. P. Truong, R. Simonutti, A. Anastasaki, Temporal Regulation of PET-RAFT Controlled Radical Depolymerization, Angew. Chem. Int. Ed. 62, e202313232 (2023),

[0023] R. Whitfield, G. R. Jones, N. P. Truong, L. E. Manring, A. Anastasaki, Solvent-Free Chemical Recycling of Polymethacrylates made by ATRP and RAFT polymerization: High-Yielding Depolymerization at Low Temperatures, Angew. Chem. Int. Ed., e202309116 (2023),

[0024] J. B. Young et al., Bulk depolymerization of poly(methyl methacrylate) via chain-end initiation for catalyst-free reversion to monomer, Chem. , Accepted (2023),

[0025] J. B. Young, J. I. Bowman, C. B. Eades, A. J. Wong, B. S. Sumerlin, Photoassisted Radical Depolymerization., ACS Macro Lett. 11, 1390-1395 (2022),

[0026] S. Huang, X. Su, Y. Wu, X.-G. Xiong, Y. Liu, Promoting halogenbonding catalyzed living radical polymerization through ion-pair strain, Chem. Sci. 13, 11352-11359 (2022),

[0027] M. J. Flanders, W. M. Gramlich, Reversible -addition fragmentation chain transfer (RAFT) mediated depolymerization of brush polymers, Polym. Chem. 9, 2328-2335 (2018),

[0028] Y. Sano, T. Konishi, M. Sawamoto, M. Ouchi, Controlled radical depolymerization of chlorine-capped PMMA via reversible activation of the terminal group by ruthenium catalyst Eur. Polym. J. 120, 109181 (2019),

[0029] G. R. Jones et al., Reversed Controlled Polymerization (RCP): Depolymerization from Well-Defined Polymers to Monomers, J. Am. Chem. Soc. 145, 9898-9915 (2023)).

[0008] These end groups, typically halogens, thiocarbonylthio compounds, or '-hydroxy phthal imide esters, can be (photo)thermally or catalytically cleaved from the polymer to form a chain-end radical that can trigger an end-to-end depolymerization.

[0009] Matyjaszewski and coworkers demonstrated in a series of reports the full potential of halogen chainends by utilizing Cu or Fe halide salt catalysts to cleave the terminal C-Cl bond and achieve >80% depolymerization in solution and bulk [see

[0012] to

[0015] ,

[0010] Sumerlin and coworkers utilized thiocarbonylthio esters to trigger depolymerization via photolytic cleavage of the terminal thiocarbonylthio C-S bond in solution and bulk (see 25], More recently, the same group demonstrated depolymerization from both ends of PMMA by utilizing an additional thermolytically labile A'-hydrox phthal imide ester at a-chain-end (see

[0024] .

[0011] Anastasaki et al. reported up to 92% depolymerization for various polymethacrylates using thiocarbonylthio and halogen-terminated chain-end in solution and bulk (see

[0016] to

[0023] ).

[0012] Despite these advances, current methods are restricted to polymers with pre-installed weak links and cannot address the 3.9 million metric tons of industrial PMMA produced annually or existing waste (-90% unrecycled) (see

[0030] J. De Tommaso, J.-L. Dubois, Risk Analysis on PMMA Recycling Economics. 13, 2724 (2021) and

[0031] M. Sponchioni, S. Altinok, in Advances in Chemical Engineering, D. Moscatelli, M. Pelucchi, Eds. (Academic Press, 2022), vol. 60, pp. 269-287).

[0013] Moreover, even if the entire industry were to immediately transition into producing such tailored materials containing weak bonds, their instability under heat / light and limited depolymerization at high molecular weights ( 105- 106g / mol) poses serious limitations for real -world applications. As a consequence, there was still a need for a process for the efficient depolymerisation of vinyl polymers in particular a process that allows depolymerisation of vinyl polymers without specially designed end groups.

[0014] Summary of the invention

[0015] A process was now found for the photo-initiated depolymerisation of vinyl polymers comprising at least the steps of:

[0016] A) providing a reaction medium comprising i) at least one vinyl polymer selected from those comprising monomer units selected from monomer units of formula (I) wherein

[0017] R1is hydrogen, methyl or -CH2COOR3and

[0018] R2if R1is hydrogen or methyl is hydrogen, methyl, cyano, Ce-Cu-aryl, - OR3, -COOR3, -CONR4R4and for hydrogen additionally also -O(C=O)R3if R1is -CH2COOR3is -COOR3or

[0019] R1and R2together are -(C=O)O-CH(CH3)-CH2-, -(C=O)O-CH2-CH(CH3)- or -(C=O)O-CH2-CH2- wherein

[0020] R3is independently selected from the group consisting of Ce-Cu-aryl, C3-Ci4- heterocyclyl or Ci-Cis-alkyl, whereby Ci-Cis-alkyl is either not, once, twice or more than twice interrupted by non-successive functional groups selected from the group consisting of:

[0021] -O-, -SO2-, -SO-, -SO2NR4-, NR4SO2-, -NR4-, -CO-, -O(CO)-, -(CO)O-, -O(CO)O-, -NR4(CO)NR4-, NR4(CO)-, -(CO)NR4-, -NR4(CO)O-, -O(CO)NR4- and which is additionally or alternatively either not, once, twice or more than twice interrupted by bivalent residues selected from the group consisting of C3-C14- heterocyclo-diyl and G -C’u-aryldiyl. and which is additionally or alternatively either not either once, twice or more than twice substituted by substituents selected from the group consisting of: hydroxy, fluoro, cyano, Ce-Cu-aryl, Ci-Cs-alkoxy, -PO(N(R4)2)2, PO(OR4)2, - SO2N(R4)2or -N(R4)2

[0022] R4is independently selected from the group consisting of hydrogen, Ci-Cs-alkyl, Ce- Ci4-aryl and G-Cu-hctcrocyclyl or N(R4)2 as a whole is a N-containing C3-C14- heterocycle, ii) and at least one chlorine-containing reagent and

[0023] B) irradiating said reaction medium with electromagnetic radiation having a wavelength sufficient to induce the generation of chlorine radicals.

[0024] The scope of the invention further encompasses a process for the recycling of vinyl polymers comprising a process according to the invention as well as the use of chlorine-containing reagents for the depolymerisation of vinyl polymers.

[0025] Brief description of the drawing

[0026] Figure 1 shows the anticipated mechanism of the depolymerization reaction according to the invention which is initiated via a hydrogen atom transfer (HAT) by a chlorine radical formed upon irradiation exemplarily shown for polymethylmethacrylate, hereinafter referred to as PMMA.

[0027] Detailed description

[0028] The scope of the invention encompasses all combinations of substituent definitions, parameters, features and illustrations set forth above and below, either in general or within areas of preference or preferred or alternative embodiments, with one another.

[0029] Whenever used herein the terms “including”, “for example”, “e.g.”, “such as” and “like” are meant in the sense of “including but without being limited to” or “for example without limitation”, respectively. The term “depolymerization” as used herein means the scission of polymer chains of the polymer employed in the inventive process into fragments having a lower molecular mass than the polymer chains of the polymer beforehand.

[0030] Such fragments having a lower molecular mass than the polymer chains of the polymer beforehand typically exhibit a lower degree of polymerization i.e. represent vinyl polymers comprising a reduced number of monomer units of formula (I) than the vinyl polymers employed into the reaction.

[0031] In a preferred embodiment depolymerization means the partial or full fragmentation of polymer chains of the polymer(s) employed in the inventive process into those monomers the polymer(s) were originally made from i.e. where the monomer units of the polymers are derived from, preferably to an extent of 20 wt-% or more, more preferably 50 wt-% or more, even more preferably 80 wt-% or more and yet even more preferably 90 wt-% or more based on the mass of polymer(s) employed.

[0032] As used herein, and unless specifically stated otherwise, Ce-Ci4-aryl denotes carbocyclic aromatic substituents having six to fourteen carbon atoms within the aromatic system as such, i.e. without carbon atoms of substituents, preferably phenyl (Ce), naphthyl (Cio), phenanthrenyl and anthracenyl (each CM), whereby said carbocyclic, aromatic substituents are unsubstituted or substituted by up to five identical or different substituents per cycle. For example and with preference, the substituents are selected from the group consisting of fluoro, cyano, Ci-Cs-alkyl, Ci-C8-fluoroalkyl, Ci-Cs- alkoxy, Ci-C8-fluoroalkoxy, Ce-Cw-aryl, in particular phenyl and naphthyl, di(Ci-C8-alkyl)amino, (Ci-C8-alkyl)amino, CO(Ci-C8-alkyl), OCO(Ci-C8-alkyl), NHCO(Ci-C8-alkyl), N(CI-C8- alkyl)CO(Ci-C8-alkyl), CO(C6-Ci4-aryl), OCO(C6-Ci4-aryl), NHCO(C6-Ci4-aryl), N(CI-C8- alkyl)CO(C6-Ci4-aryl), COO-(Ci-C8-alkyl), COO-(C6-Ci4-aryl), CON(Ci-C8-alkyl)2or CONH(Ci-C8-alkyl), CONH2, SO2NH2and SO2N(Ci-C8-alkyl)2. In a preferred embodiment, the carbocyclic, aromatic substituents are unsubstituted or substituted by up to three identical or different substituents per cycle selected from the group consisting of fluoro, cyano, Ci-C8-alkyl, Ci-C8- fluoroalkyl, Ci-C8-alkoxy, Ci-C8-fluoroalkoxy, Ce-Cw-aryl, in particular phenyl.

[0033] In a more preferred embodiment the carbocyclic, aromatic substituents are unsubstituted or substituted by up to three identical or different substituents per cycle selected from the group consisting of fluoro, Ci-C8-alkyl, Ci-C8-perfluoroalkyl, Ci-C8-alkoxy, Ci-C8-perfluoroalkoxy, and phenyl.

[0034] Most preferred carbocyclic, aromatic substituents are phenyl.

[0035] The definitions given above including their areas of preference also apply analogously to Ce-Ci4- aryl-diyl substituents.

[0036] As used herein and unless specifically stated otherwise, OCu-heterocyclyl denotes heterocyclic aliphatic, aromatic or mixed aliphatic and aromatic substituents in which no, one, two or three skeleton atoms per cycle, but at least one skeleton atom in the entire cyclic system is a heteroatom selected from the group consisting of nitrogen and oxygen and whereby the entire cyclic system as such, i.e. without carbon atoms of substituents, comprises three to fourteen carbon atoms and whereby the heterocyclic aliphatic, aromatic or mixed aliphatic and aromatic substituents are unsubstituted or substituted by up to five identical or different substituents per cycle, whereby the substituents are selected from the same group as given above for carbocyclic aromatic substituents including the areas of preference.

[0037] Preferred heterocyclyl-substituents are pyridinyl, oxazolyl, benzofuranyl, dibenzofuranyl, furanyl, indolyl, pyridazinyl, pyrazinyl, imidazolyl, pyrimidinyl and quinolinyl, either unsubstituted or substituted with up to three substituents selected from the group consisting of fluoro, Ci-Cs-alkyl, Ci-Cs-perfluoroalkyl, Ci-Cs-alkoxy, Ci-Cs -perfluoroalkoxy, and phenyl.

[0038] As used herein, and unless specifically stated otherwise, Ci-Cis.alkyl, Ci-Cis-alkoxy are a straight- chained, cyclic either in part or as a whole, branched or unbranched alkyl or alkoxy substituents having the given number of carbon atoms in the substituent as such, i.e. without carbon atoms of further, optionally present substituents or carbon atoms of functions interrupting the aforementioned substituents. As an example, a benzyl substituent represents a Ci-alkyl substituent substituted by phenyl.

[0039] The same analogously applies to Ci-Cs-alkyl and Ci-C4-alkyl, Ci-Cs-alkoxy and Ci-C4-alkoxy substituents.

[0040] Fluoroalkyl or fluoroalkoxy substituents denote alkyl or alkoxy substituents with the given number of carbon atoms which are once or more than once, preferably fully substituted by fluoro substituents.

[0041] Fluoroalkyl or fluoroalkoxy substituents denote alkyl or alkoxy substituents with the given number of carbon atoms which are once or more than once, preferably fully substituted by fluorine.

[0042] Perfluoroalkyl or perfluoroalkoxy substituents denote alkyl or alkoxy substituents with the given number of carbon atoms which are fully substituted by fluoro substituents.

[0043] Specific examples of Ci-Cs-alkyl are methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclohexyl, n-hexyl, n-heptyl, n-octyl and isooctyl. Additional examples for Ci -Cis-alkyl are norbomyl, adamantyl, n-decyl, n-dodecyl alkyl, n-hexadecyl, n-octadecyl.

[0044] Specific examples of Ci-Cs-alkoxy-substituents are methoxy, ethoxy, isopropoxy, n-propoxy, n- butoxy, tert-butoxy and cyclohexyloxy.

[0045] The vinyl polymerfs)

[0046] In step A), a reaction medium is provided which comprises not only at least one chlorine-containing reagent but also at least one vinyl polymer. The vinyl polymer is selected from those comprising monomer units selected from those of formula (I) as defined above.

[0047] In a preferred embodiment such monomer units make up at least 50 wt-%, more preferably at least 80 wt.-% and even more preferably at least 90 wt.-% and yet even more preferably at least 95 % of the total mass of vinyl polymer employed.

[0048] The remainder to 100 %, if any, may include monomer units other than those of formula (I) or compounds selected from the group of known polymer additives which includes flame-retardants, anti-aging agents like antioxidants, antiozonants, heat stabilizers and light stabilizers, processing aids like lubricants, hydrocarbon waxes and fatty acids, plasticizers, tackifiers, pigments, colorants, antistatic agents, anti-microbials and odor agents.

[0049] It is an important finding that said polymer additives, in particular anti -aging agents like antioxidants, antiozonants, heat stabililizers and light stabilizers which are known to scavenge ozone, oxygen or certain other radicals do not prevent depolymerization if for example used in typical amounts.

[0050] In one embodiment the vinyl polymers employed contain 2.5 wt-% or less, preferably 1.5 wt.-% or less, more preferably 1.0 wt.-% or less of polymer additives selected from the group of antioxidants, antiozonants, heat stabililizers and light stabilizers.

[0051] It is apparent to those skilled in the art that the end groups typically do not contribute more than 0.5 wt.-% to the total weight of the vinyl polymer. Therefore vinyl polymers that are prepared from only one specific monomer resulting in one specific monomer unit would typically and independently of their typically small end groups be made up from 100 % of such single monomer unit since 100 % is a rounded value for anything from 99.5 wt.-% or more.

[0052] Typical end groups depend on the vinyl polymer and their polymerization process and include hydrogen, hydroxyl, alkenes e.g. formed by disproportionation, halogens, thiols, thiocarbonylthio compounds, or JV-hydroxyphthalimide esters or (other) fragments of an initiator molecule such as 2- cyano-propyl.

[0053] In one embodiment the vinyl polymer employed in the process according to the invention does not comprise end-groups comprising a halogen or a cyano group or a '-hydroxy phthal imidc-group or an azo group or a sulfur, in particular a thiocarbonylthio group.

[0054] Preferred monomer units are those of formula (I) wherein

[0055] R1methyl or -CH2COOR3and

[0056] R2if R1is methyl is methyl, phenyl, -OR3, -COOR3, -CONR4R4if R1is -CH2COOR3is -COOR3or R1and R2together are -(C=O)O-CH(CH3)-CH2- wherein R3and R4are as defined above, but preferably

[0057] R3is independently selected from the group consisting of phenyl or Ci -Cis-alkyl and

[0058] R4is independently selected from the group consisting of hydrogen, Ci-Cs-alkyl and phenyl

[0059] Even more preferred monomer units are those of formula (I) wherein

[0060] R1is methyl and

[0061] R2is methyl, phenyl, -OR3, -COOR3, -CONR4R4, preferably COOR3wherein R3and R4are as defined above in the summary of the invention, but preferably

[0062] R3is independently selected from the group consisting of phenyl or Ci -Cis-alkyl and more preferably methyl

[0063] R4is independently selected from the group consisting of hydrogen, Ci-Cs-alkyl and phenyl and more preferably hydrogen and methyl.

[0064] In one embodiment the monomer units are derived from

[0065] • Methacrylic acid esters, amides and nitriles, such as methyl-, ethyl-, -isopropyl, n-butyl-, 2- ethylhexyl-, 2-hydroxyethyl and isobomylmethacrylate, methacrylamide, N- isopropylmethacrylamide and methacrylonitrile;

[0066] • itaconic acid di Ci-Cis-alkyl esters;

[0067] • vinyl ethers, such as ethyl vinyl ether and isobutyl vinyl ether;

[0068] • isopropenylethers such as methyl-, ethyl, isopropyl-, n-butyl, isobutyl- ethylhexyl-, decyl-, dodecyl- and benzylisopropenylether;

[0069] • vinyl esters, such as vinyl acetate;

[0070] • vinyl aromatic compounds such as vinylpyridine, a-methylstyrene, styrene and styrene substituted by Ci-Cs-alkoxy at the aromatic ring, preferably styrene, 2-, 3- and 4- chlorostyrene and p-methoxystyrene;

[0071] • vinylic olefins such as ethene, propene and isobutylene; vinylic lactones such as y-methyl-a-methylene-y-butyrolactone, p-methyl-a-methylene-y- butyrolactone and a-methylene-y-butyrolactone. Preferably, the monomer units are derived from methacrylic acid Ci-Cis-alkylesters such as methyl-, ethyl-, isopropyl-, n-butyl-, 2-ethylhexyl- and isobomyhnethacrylate, methacrylamide, N-isopropyl- methacrylamide, itaconic acid Ci-di Cis-alkylesters such as itaconic acid dimethyl ester and itaconic acid diethyl ester, a-methylstyrene, isobutylene as well as isopropenyl-Ci-Cis-alkylethers such as methyl-, ethyl, isopropyl-, n-butyl, isobutyl-, ethylhexyl-, decyl- and dodecylisopropenylether.

[0072] Specific preferred examples of vinyl polymers include polymethylmethacrylate (PMMA), polyethylmethacrylate (PEMA), polyisopropylmethacrylate, poly-n-butylmethacrylate, poly-2- ethylhexylmethacrylate, poly-isobomylmethacrylate, polymethacrylamide, poly-N-isopropyl- methacrylamide, poly-a-styrene, polyisobutylene, poly-dimethylitaconate and poly- diethylitaconate, poly-y-methyl-a-methylene-y-butyrolactone, poly-P-methyl-a-methylene-y- butyrolactone and poly-a-methylene-y-butyrolactone or any co-polymers of the aforementioned polymers, whereby polymethylmethacrylate (PMMA) is particularly preferred.

[0073] The vinyl polymers employed into step A) may stem from various sources including used vinyl polymers, polymers from production residues, recycled waste materials and the like. It is a major finding that the process according to the invention is qutre robust with regard to adherent traces of water, dust, dirt or other components typically accompanying waste or used materials.

[0074] The spatial dimensions, shape and morphology of the vinyl polymers are in principle not limited with regard to their general suitability to be employed in the process according to the invention. As a consequence the vinyl polymers may be for example employed as powders, granules, flakes, shredded material, chips, as bulk material or as foam, foils, sheets or any type of semi-finished or finished products.

[0075] The particle size may range from 10 nm to Im, preferably from 10 pm to 10 cm and more preferably from 1 mm to 5 cm as determined by sieving with the respective sieve size.

[0076] The vinyl polymers may be homopolymers or copolymers i.e. vinyl polymers comprising monomer units derived from two or more monomers.

[0077] In one embodiment the vinyl polymers employed in the process according to the invention comprise at least 80 wt-%, preferably at least 90 wt-%, more preferably at least 95 wt-% and even more preferably at least 97 wt-% of only one monomer unit of formula (I) as defined above including its preferential embodiments, the remainder comprising end groups, further monomer units of formula (I) and / or monomer units other than those of formula (I) and / or the polymer additives described above.

[0078] For example, typical qualities of PMMA comprise 98.5 wt.-% to 99.5 wt.-% of monomer units derived from methacrylic acid and from 0.5 to 1.5 wt.-% of n-butylacrylate. The vinyl polymers may further be linear or branched, with an average number of branching points being in the range of more than 0 and 1 or less per 100 monomer units of the polymer. Preferred vinyl polymers are linear polymers.

[0079] In one embodiment the vinyl polymers may be crosslinked as defined below or not, preferably they are not crosslinked.

[0080] If the vinyl polymers are crosslinked the term "crosslinked" refers to a vinyl polymer whose polymer chains are joined together by covalent chemical bonds, typically via crosslinking molecules or groups, to form a network polymer and whereby the average number of crosslinks is in the range of more than 0 and 3 or less per 100 monomer units of the vinyl polymer, preferably more than 0 and 1 or less per 100 monomer units of the vinyl polymer.

[0081] Generally branching and crosslinking can be induced during polymerization by multifunctional monomers as described below.

[0082] Suitable multifunctional monomers include poly(meth)acrylates such as ethylene glycol diacrylate, 1,6-hexanediol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, hexamethylene glycol diacrylate and bis- phenol-A diacrylate, 4,4'-bis(2- acryloyloxyethoxyjdiphenylpropane, trimethylolpropane tri-acrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, vinyl acrylate, polyethyleneglycol-mono-acrylate, polyethylene-glycol- di-acrylate, ethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, propylene glycol dimethacrylate, dipropylene glycol dimethacrylate, tripropylene glycol dimethacrylate, neopentyl glycol dimethacrylate, hexamethylene glycol dimethacrylate and bis- phenol-A dimethacrylate, 4,4'- bis(2-methacryloyloxyethoxy)diphenylpropane, trimethylolpropane tri-methacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, vinyl methacrylate, polyethyleneglycol-mono- methacrylate, polyethylene-glycol-di-methacrylate; and other multiolefms such as butadiene, isoprene, chloroprene, 2,4-dimethylbutadiene, cyclopentadiene, methylcyclopentadiene, cyclohexadiene, divinyl -benzene, 1 -vinyl -cyclohexadiene, norbomadiene, 2-isopropenylnorbomene, 2-vinyl-norbomene, diisopropenylbenzene, divinyltoluene, divinylxylene and Ci to C20 alkyl-substituted derivatives of the aforementioned divinylaromatic multiolefms, divinyl succinate, diallyl phthalate, triallyl phosphate, triallyl isocyanurate, ethyleneglycoldivinylether, diethyleneglycoldivinylether, triethylene-glycoldivinylether and any mixture of the aforementioned poly(meth)acrylates and / or multiolefms.

[0083] The number average molecular weight [Mn] of the vinyl polymer(s) is typically and preferably 5 kg / mol or more, for example from 10 kg / mol to 10,000 kg / mol or 20 kg / mol to 5,000 kg / mol, preferably 20 kg / mol more, for example from 20 kg / mol to 2,000 kg / mol or 20 kg / mol to 1,000 kg / mol.

[0084] The PDI is not critical per se. The polydispersity index (PDI) [Mw / Mn] of the vinyl polymers may be for example in the range of 1.00 to 10.00, preferably from 1.01 to 5.00, more preferably in the range of 1.01 to 3.00.

[0085] The chlorine -containing reagent(s)

[0086] In step A), a reaction medium further at least one chlorine-containing reagent is provided.

[0087] The chlorine-containing reagent may be any compound that is capable of producing chlorine radicals upon irradiation with electromagnetic radiation having a wavelength of 490 nm or less.

[0088] Suitable compounds include elemental chorine (Ch) and organic compounds bearing at least one N- C1 bond and / or at least one C-Cl bond.

[0089] In another embodiment suitable compounds include metal chlorides, in particular chlorides of transition metals and lanthanides.

[0090] Suitable transition metal chlorides include TiC’E. TiCT. VCI4, VCI3, CrCE, CrCT. MnCE, MnCT. FeCh, FeCl2, C0CI3, C0CI2, NiCh, NiCl2, CuCl2, CuCl, ZnCl2, whereby FeCh, FeCl2and CuCl2are preferred. The fomulae of metal chlorides listed hererein include the water-free forms as well as all existing hydrates, whereby the water-free forms are preferred.

[0091] Suitable lanthanide chlorides include LaCT. CeCE, PrCE, NdCls, NdCl2, SmCE, SmCl2, EuCE, EuCE, GdCE, TeCE, DyCl3, DyCl2, H0CI3, ErCl3, TmCE. YbCE, YbCl2, LuCl2; whereby CeCl3is preferred.

[0092] Other suitable metal chlorides include AICI3.

[0093] Suitable organic compounds include mono, di- or higher chlorinated Ce-Cio-aryl compounds as well as mono, di or higher chlorinated Ci-Cis-chloroalkanes as well as N-chloroamines, N-chloroamides and N-chloroimides such as trichloroisocyanuric acid and N-chlorophthalimide and N- chlorosuccinimide; N-chloroimines such as 2,6-dichloroquinone-4-chloroimide and N- chlorosulfonamides such as chloroamine T and 2-chloro- l .2-bcnzisothiazol-3(2 / / )-onc 1,1 -dioxide (N -chlorosaccharin) .

[0094] In a preferred embodiment the chlorine-containing reagents are capable of dissolving the vinyl polymer(s) employed in step A) at least partially at the reaction temperature applied so that the chlorine-containing reagent simultaneously serves as a solvent and as reactant to produce chlorine radicals. In one embodiment the chlorine -containing reagent is selected such that at 20°C the solubility of the vinyl polymer to be depolymerized is at least 0.5 wt.-%, preferably at least 5 wt.-% and more preferably at least 10 wt.-% based on the weight of the chlorine -containing reagent employed.

[0095] Specific examples include chlorobenzene, 1,2-dichlorobenzene, 1,3 -dichlorobenzene and 1,4- dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, 1 -chloronaphthalene, 2-chloronaphthalene, 3 -chloronaphthalene, 1,8-dichloronaphthalene, 1,2-dichloronaphthalene 2,3-dichloronaphthalene 2,6-dichloronaphthalene, 1,1,2,2-tetrachloroethane, benzotrichloride, benzodichloride and benzylchloride, whereby 1,2-dichlorobenzene, 1,2,4-trichlorobenzene and 1,1,2,2-tetrachloroethane are preferred.

[0096] Further optional components of the reaction medium

[0097] The reaction medium may further comprise an inert solvent in particular in embodiments where the chlorine-containing reagent does not serve as a solvent.

[0098] Suitable inert solvents include fluorinated aromatic compounds, fluoroalkanes or fluoroamines or mixtures of any of the aforementioned. Specific examples include fluorobenzene, 1,2- difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4- trifluorobenzene and 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, perfluoroperhydrophenanthrene, perfluorotripentylamine and perfluorodecaline and any mixtures thereof.

[0099] Further suitable inert solvents include aromatic nitriles such as benzonitrile, phthalonitrile, acetonitrile, 4-phenylbenzonitrile and any mixtures thereof.

[0100] Further suitable inert solvents include mixtures of at least one fluorinated aromatic compound and at least one aromatic nitrile.

[0101] In view of the proposed mechanism and the experimental part, the reaction medium should not or just to a minor extent include compounds that would compete or react with the chlorine radicals produced in step B). Preferably the weight ratio of vinyl polymer to such reactive compounds is 0.1 or higher, preferably 1 or higher, more preferably 5 or higher and even more preferably 20 or higher. In one embodiment such reactive compounds are absent, whereby absent as used herein means that the weight ratio of vinyl polymers to such reactive compounds is 100 or higher.

[0102] Preparation and reaction conditions The preparation of the reaction medium is typically effected by simply mixing the vinyl polymer(s) and the at least one chlorine -containing reagent by standard mixing elements such as agitators, static mixers or combinations thereof such as rotor-stator mixers. Even though not typically necessary, the mixing can be supported by using high force dispersion devices such as, for example, ultrasound sonotrodes or high pressure homogenizers.

[0103] In an embodiment, the reaction medium forms a solution or dispersion, whereby the formation of a solution is preferred. It is noteworthy that even in cases where the vinyl polymer(s) are not fully dissolved in the reaction mixture, a solution is frequently formed during step B) i.e. upon depolymerisation.

[0104] The preparation of the reaction medium in step A) may either be performed batchwise or continuously, whereby, in one embodiment, the continuous preparation is preferred.

[0105] The weight ratio of the vinyl polymer(s) and the chlorine -containing reagent is typically from 100: 1 to 1: 10.000.

[0106] In embodiments wherein the chlorine -containing reagent simultaneously serves as a solvent the weight ratio of the vinyl polymer(s) and the chlorine-containing reagent is typically from 1 : 1 to 1 : 10,000, preferably from 1 :4 to 1 : 1,000, more preferably from 1:4 to 1 :200 or from 1 :5 to 1 : 100.

[0107] In embodiments wherein the chlorine-containing reagent does not serve as a solvent e.g. for chlorine the weight ratio of the vinyl polymer(s) and the chlorine-containing reagent is typically from 600: 1 to 1: 1, preferably from 100: 1 to 1: 1, more preferably from 100: 1 to 5: 1 such as from 10: 1 to 25: 1.

[0108] The presence of a solvent whether in form of the chorine containing reagent or an inert solvent is not mandatory per se. However to ensure a smooth reaction the reaction medium should comprise a liquid phase under reaction conditions. This can also be effected with a melt of the vinyl polymer.

[0109] In step B), the one or more vinyl polymers present in the reaction medium are depolymerized by irradiating said reaction medium with electromagnetic radiation having a wavelength sufficient to induce the generation of chlorine radicals.

[0110] It is apparent to those skilled in the art, that the electromagnetic radiation sufficient to induce the generation of chlorine radicals is dependent on the exact structure of the chlorine-containing reagent but can easily determined by performing very few and commonly known simple measurements, tests or experiments. Such tests include UV-Vis spectroscopy and radical scavenger experiments known to those skilled in the art.

[0111] For example, chlorine radicals can be generated already with a wavelength of around 490 nm from elemental chlorine while the generation of chlorine radicals from 1,2-dichlorobenzene starts from around 430 nm or below.

[0112] As a consequence, and in order to carry out the process according to the invention one may either adapt the chlorine-containing reagents to a given source of electromagnetic radiation or vice versa.

[0113] For typical chlorine -containing reagents as described hereinabove the generation of radicals is typically induced by irradiation having a wavelength of 500 nm or below, preferably 450 nm or below, more preferably in the range of 250 to 440 nm, even more preferably in the range of 300 to 430 nm.

[0114] Suitable sources of electromagnetic radiation having a wavelength sufficient to induce the generation of chlorine radicals include eximer lasers such as KrF and XeF-lasers; UV lamps like low-pressure, medium-pressure, high-pressure and super-high-pressure mercury lamps which can be undoped or doped e.g. with gallium iodide, thallium iodide or other metal halides; blue, violet-blue or UV-LEDs; concentrated, direct or indirect sunlight; xenon or xenon mercury arc lamps such as continuous- output xenon short- or long-arc lamps, flash lamps such as xenon or xenon mercury flash lamps; microwave-excited metal vapour lamps; excimer lamps, superactinic fluorescent tubes; fluorescent lamps; and noble gas incandescent lamps.

[0115] Preferred sources are UV lamps like low-pressure, medium-pressure, high-pressure and super-high- pressure mercury lamps which can be undoped or doped e.g. with gallium iodide, thallium iodide or other metal halides; blue, violet-blue or UV-LEDs, xenon or xenon mercury arc lamps such as continuous-output xenon short- or long -arc lamps.

[0116] In an embodiment, multichromatic sources of electromagnetic radiation are used to generate chlorine radicals.

[0117] As used herein a multichromatic sources of electromagnetic radiation denotes a source emitting electromagnetic radiation having more than one relative emission maxima (also known as emission bands) preferably more than one relative emission maxima within the wavelength ranges disclosed above. Even though the conditions mentioned above are sufficient to allow the depolymerization to proceed it is apparent to those skilled in the art that chlorine radical formation depends on the intensity and / or the time of irradiance.

[0118] In an embodiment of the invention the irradiance with electromagnetic radiation sufficient to induce the generation of chlorine radicals is effected at average intensities of at least 5 W per square meter of irradiated surface of the reaction medium (5 W / m2), preferably at least 10 W / m2and more preferably from 20 W / m2to 10 kW / m2.

[0119] In a preferred embodiment irradiance is effected with electromagnetic radiation having a wavelength of 450 nm or below, preferably of 440 nm or below, more preferably in the range of 250 to 440 nm, even more preferably in the range of 300 to 430 nm at average intensities of at least 5 W per square meter of irradiated surface of the reaction medium (5 W / m2), preferably at least 10 W / m2and more preferably from 20 W / m2to 10 kW / m2.

[0120] The irradiation time of the reaction medium may vary depending on the surface to volume ratio of the reactor employed as well as on and the intensity of irradiance but typically is for example in the range of from 1 min to 48 h, preferably 15 min to 36 h and even more preferably from Ih to 24 h min. Longer exposure times typically do not positively affect the depolymerization.

[0121] The determination of a suitable reaction temperature during depolymerization in step B) depends on the composition of the reaction medium, in particular the type and concentration of the vinyl polymer(s) within the reaction medium, since these factors mainly determine the thermodynamics of the depolymerisation which is entropy driven.

[0122] A typical and preferred reaction temperature range to carry out the depolymerisation in step B) is from -30 to 250° C, preferably from 20 to 220° C and even more preferably from 70 to 180° C.

[0123] In another embodiment the reaction temperature is from 90 to 170°C.

[0124] A typical and preferred reaction pressure range to carry out the depolymerization according to step B) is from 100 hPa to 5 MPa, preferably from 500 hPa to 1 MPa and more preferably from 900 hPa to 0.5 MPa, for example at ambient pressure.

[0125] In one embodiment, the depolymerization carried out such that a monomer production of 20 to 100 wt-% with regard to the vinyl polymer(s) employed is achieved, preferably 50 to 100 wt-%, more preferably 80 to 100 wt.-% and even more preferably 90 to 99 %.

[0126] In one embodiment the reaction is carried out under substantial exclusion of oxygen. As used herein substantial exclusion means a partial pressure of oxygen in the reaction vessel of 50 hPa or less, preferably 10 hPa or less and more preferably 1 hPa or less.

[0127] In one embodiment the reaction is carried out under an inert gas such as nitrogen or argon or any mixtures thereof. The aforementioned partial pressures of oxygen are for example ensured by flushing the reaction vessel once or several times with an inert gas such as nitrogen or argon or any mixtures thereof.

[0128] Steps A) and B) can independently of each other be carried out batchwise or continuously.

[0129] In one embodiment step B) is carried out continuously using a flow-through photo-reactor.

[0130] In those embodiments where a flow-through reactor is employed, the flow rate is adjusted to an average flow velocity of 0.005 to 1 m / s, preferably 0.01 to 0.5 m / s.

[0131] The process can be carried out using every type of device designed to carry out step B) and optionally but preferably also step A) under the conditions described hereinabove.

[0132] This includes photo-reactors known to those skilled in the art having irradiation zones with dimensions to allow irradiation with the parameters set forth above.

[0133] Suitable types of photo-reactors include rising or falling film photo-reactors and flow-through reactors, in particular microfluidic devices.

[0134] Suitable flow-through reactors comprise any device comprising in flow direction an inlet, at least one irradiation zone comprising a wall material transparent to the electromagnetic radiation employed such as simple tubes, tubings or hoses and an outlet as well as means to convey the reaction medium form the inlet via the at least one exposure zone to the outlet such as pumps.

[0135] Suitable wall material transparent to the electromagnetic radiation generating chlorine radicals include polyolefins such as fluorinated polyolefins such as fluorinated poly(ethylene-co-propylene), hereinafter also denoted as FEP, and polytetrafluoroethylene, polyesters (including polycarbonates), polyacrylates, polyurethanes and glass such as quartz glass, borax containing glasses and other glasses which are at least partially transparent to the electromagnetic radiation employed.

[0136] Examples of suitable flow-through reactors include the flow-through reactors disclosed in US2008 / 013537, US2003 / 0118486 and US2003 / 0042126.

[0137] In a preferred embodiment the flow-through reactors further comprise at least one mixing device to carry out step A) which is in flow direction arranged before the at least one irradiation zone. Said mixing zones may be equipped with the standard mixing elements mentioned above. In a preferred embodiment the mixing zone comprises static mixing elements such as slit type mixers.

[0138] In another embodiment steps A) and B) are carried out batch-wise in a photo-reactor. An exemplary photo-reactor is described in the experimental part.

[0139] As a result of the depolymerization of step B) polymer chain fragments or preferably monomers are obtained.

[0140] Monomers, if present, are preferably removed from the resulting reaction medium by standard stripping, vacuum or distillation techniques, preferably already during step B) to shift the equilibrium towards depolymerisation.

[0141] Polymer chain fragments, if present, may be recycled into step A) to further fragment the polymer chains and / or to produce further monomer(s).

[0142] In one embodiment, the monomers produced during step B) are collected and used in a process to produce vinyl polymers.

[0143] Therefore, the invention further comprises a process for the production of compounds of formula (II) wherein R1and R2have the meaning as defined for formula (I) including their preferential embodiments by photo-depolymerization of vinyl polymers comprising monomer units of formula (I).

[0144] A further aspect of the invention further relates to a recycling process for vinyl polymers comprising at least the process according to the invention.

[0145] Yet another aspect of the invention relates to the use of chlorine-containing reagents for the depolymerization of vinyl polymers.

[0146] Mechanistic aspects

[0147] In order to provide a better understanding of the invention, some mechanistic aspects are discussed exemplarily for the depolymerisation of PMMA, which, however, in no way shall be binding or be deemed as limiting feature.

[0148] Upon exposure to electromagnetic radiation, a chlorine radical is generated via photolysis of the at least one chlorine-containing reagent present in the reaction mixture. This chlorine radical abstracts either a methyl or methylene hydrogen of the polymer backbone to form a carbon-centered backbone radical. Electron paramagnetic resonance (EPR) experiments confirmed the formation of a carboncentered polymeric radical.

[0149] From the experimental results set forth hereinbelow it seems likely that the secondary methylene radical is the major radical as a methyl -methylene radical transition can occur via intramolecular hydrogen transfer (see

[0032] P. Ulanski, E. Bothe, K. Hildenbrand, C. von Sonntag, Free-Radical- Induced Chain Breakage and Depolymerization of Poly(methacrylic acid): Equilibrium Polymerization in Aqueous Solution at Room Temperature, Chemistry - A European Journal 6, 3922-3934 (2000)). Subsequently, p-scission of the backbone C-C bond produces an alkene and primary radical fragment, the latter of which can continue undergoing a series of P-scissions to produce the monomer MMA. The generation of MMA through a reactive primary radical is surprising as PMMA depolymerization typically occurs via the more stable tertiary radical. However, previous reports on the aqueous depolymerization of polymethacrylic acid (see

[0032] ) make these pathways at least not unlikely. A schematic view on the assumed reaction mechanism is shown in Fig. 1.

[0150] The present invention is a major contribution to modem recycling technologies since a one-step universal closed-loop chemical recycling methodology was provided that do not rely on tailor-made polymers containing labile bonds. The invention allows to revert commercial vinyl polymers back to the respective monomers even in the presence of undisclosed or unconventional comonomers, additives and dyes. Through the inventive approach, near-quantitative depolymerization can be achieved for vinyl polymers such as PMMA with high molecular weights up to 106g / mol and whether pristine or with a thermal history.

[0151] The invention is further illustrated by the examples without being limited thereby.

[0152] Examples:

[0153] I General Materials and Methods

[0154] A transparent quartz glass beaker fdled with transparent silicon oil was surrounded with LEDs producing electromagnetic radiation with wavelengths of either 365, 395, 415 nm, or 460+ nm (i.e. RGB-LEDs). The glass test tubes described below were immersed into the silicon oil and the glass beaker and the oil heated to the given temperature using a heating plate.

[0155] PMMA was either purchased from Rohm (Plexiglas®, Mnof 264,000 g / mol, acrylates could not be detected) or synthesized by free radical polymerization with azobisisobutyronitrile as the initiator (Mnof 330,000 g / mol, with no acrylates present in the polymer). II Photoinitiated depolymerization

[0156] Examples 1 to 17

[0157] In a glass test tube, 10 mg of the synthesized PMMA, 10 mL of a solvent, and a stir bar were added. A septum was used to seal the glass tube and the solution was stirred until all the PMMA dissolved. The solution was deoxygenated by sparging the solution with nitrogen through a stainless steel needle for 15 minutes and subsequently placed into the photoreactor described above. The reaction medium was then exposed to irradiation with electromagnetic radiation having the wavelength indicated in table 1 for 24 h and at the temperature also indicated in table 1.

[0158] Table 1: * for comparison: Not according to the invention

[0159] 1) instead of 10 mg PMMA, 100 mg PMMA were employed.

[0160] 2) commercial Plexiglas® (either yellow (Ex. 12), blue (Ex. 13), red (Ex. 14) or green (Ex. 15)) was used instead of synthesized PMMA.

[0161] 3) a mixture of commercial Plexiglas (yellow, blue, red, green) was used at a concentration of 16 g / 80 mL of solvent. MMA was distilled from the reaction mixture periodically.

[0162] 4) instead of 10 mg PMMA, 100 mg of blue-colored Plexiglas® were employed.

Claims

Claims:

1. A process for the photo-initiated depolymerisation of vinyl polymers comprising at least the steps of:A) providing a reaction medium comprising i) at least one vinyl polymer selected from those comprising monomer units selected from monomer units of formula (I)whereinR1is hydrogen, methyl or -CH2COOR3andR2if R1is hydrogen or methyl is hydrogen, methyl, cyano, Ce-Cu-aryl, - OR3, -COOR3, -CONR4R4and for hydrogen additionally also -O(C=O)R3if R1is -CH2COOR3is -COOR3orR1and R2together are -(C=O)O-CH(CH3)-CH2-, -(C=O)O-CH2- CH(CH3)- or -(C=O)O-CH2-CH2- whereinR3is independently selected from the group consisting of Ce-Cu-aryl, C3- C14- heterocyclyl or Ci-Cis-alkyl, whereby Ci-Cis-alkyl is either not, once, twice or more than twice interrupted by non-successive functional groups selected from the group consisting of:-O-, -SO2-, -SO-, -SO2NR4-, NR4SO2-, -NR4-, -CO-, -O(CO)-, -(CO)O-, -O(CO)O-, -NR4(CO)NR4-, NR4(CO)-, -(CO)NR4-, -NR4(CO)O-, - O(CO)NR4- and which is additionally or alternatively either not, once, twice or more than twice interrupted by bivalent residues selected from the group consisting of Cs-Cw-heterocyclo-diyl and C -C’u-aryldiyl.and which is additionally or alternatively either not either once, twice or more than twice substituted by substituents selected from the group consisting of: hydroxy, fluoro, cyano, Ce-Cw-aryl, Ci-Cs-alkoxy, -PO(N(R4)2)2, PO(OR4)2, -SO2N(R4)2or -N(R4)2R4is independently selected from the group consisting of hydrogen, Ci-Cs- alkyl, Ce-Ci4-aryl and Cs-Cu-hctcrocyclyl or N(R4)2 as a whole is a N- containing Cs-Cu-hctcrocyclc. ii) and at least one chlorine -containing reagent andB) irradiating said reaction medium with electromagnetic radiation having a wavelength sufficient to induce the generation of chlorine radicals.

2. The process according to claim 1, wherein the monomer units as defined in claim 1 make up at least 50 wt-%, more preferably at least 80 wt.-% and even more preferably at least 90 wt.-% and yet even more preferably at least 95 % of the total mass of vinyl polymer.

3. The process according to claim 1 or 2, wherein the monomer units are those of formula (I) whereinR1methyl or -CH2COOR3andR2if R1is methyl is methyl, phenyl, -OR3, -COOR3, -CONR4R4if R1is -CH2COOR3is -COOR3orR1and R2together are -(C=O)O-CH(CH3)-CH2- wherein R3and R4are as defined above, but preferablyR3is independently selected from the group consisting of phenyl or Ci-Cis-alkyl andR4is independently selected from the group consisting of hydrogen, Ci-Cs-alkyl and phenyl4. The process according to any one of claims 1 to 3, wherein the monomer units are those of formula (I) whereinR1is methyl andR2is methyl, phenyl, -OR3, -COOR3, -CONR4R4, preferably COOR3wherein R3and R4are as defined above in claim 1, but preferablyR3is independently selected from the group consisting of phenyl or Ci-Cis-alkyl and more preferably methylR4is independently selected from the group consisting of hydrogen, Ci-Cs-alkyl and phenyl and more preferably hydrogen and methyl.

5. The process according to any one of claims 1 to 4, wherein the vinyl polymers are selected from polymethylmethacrylate (PMMA), polyethylmethacrylate (PEMA), polyisopropylmethacrylate, poly-n-butylmethacrylate, poly-2-ethylhexylmethacrylate, poly- isobomylmethacrylate, polymethacrylamide, poly-N-isopropyl-methacrylamide, poly-a- styrene, polyisobutylene, poly- dimethylitaconate and poly-diethylitaconate or any copolymers of the aforementioned polymers, whereby polymethylmethacrylate (PMMA) is preferred.

6. The process according to any one of claims 1 to 5, wherein the vinyl polymers are employed as powders, granules, flakes, shredded material, chips, as bulk material or as foam, foils, sheets or any type of semi-finished or finished products.

7. The process according to any one of claims 1 to 6, wherein the vinyl polymer has a number average molecular weight [Mn] of 5 kg / mol or more, for example from 10 kg / mol to 10,000 kg / mol or 20 kg / mol to 5,000 kg / mol, preferably 20 kg / mol or more, for example from 20 kg / mol to 2,000 kg / mol or 20 kg / mol to 1,000 kg / mol.

8. The process according to any one of claims 1 to 7, wherein the chlorine-containing reagent is selected from the group consisting of elemental chorine (CT) and organic compounds bearing at least one N-Cl bond and / or at least one C-Cl bond.

9. The process according to any one of claims 1 to 8, wherein the chlorine-containing reagent simultaneously serves as a solvent and as reactant to produce chlorine radicals and is preferably selected from the group consisting of chlorobenzene, 1,2-dichlorobenzene, 1,3- dichlorobenzene and 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, 1- chloronaphthalene, 2-chloronaphthalene, 3 -chloronaphthalene, 1,8-dichloronaphthalene, 1,2-dichloronaphthalene 2,3-dichloronaphthalene 2,6-dichloronaphthalene, 1, 1,2,2- tetrachloroethane, benzotrichloride, benzodichloride and benzylchloride, whereby 1,2- dichlorobenzene, 1,2,4-trichlorobenzene and 1,1,2,2-tetrachloroethane are particularly preferred.

10. The process according to any one of claims 1 to 9, wherein in the reaction medium the weight ratio of vinyl polymer to reactive compounds being capable of reacting with chlorine radicals is 0. 1 or higher, preferably 1 or higher, more preferably 5 or higher and even more preferably 20 or higher.

11. The process according to any one of claims 1 to 10, wherein the weight ratio of the vinyl polymer(s) and the chlorine-containing reagent is, if the chlorine-containing reagent simultaneously serves as a solvent from 1 : 1 to 1 : 10.000, preferably from 1 :4 to 1 : 1000, more preferably from 1 :4 to 1 :200 or from 1 :5 to 1 : 100 or, if the chlorine-containing reagent does not serve as a solvent from 100: 1 to 1: 1, preferably from 100: 1 to 5: 1.

12. The process according to any one of claims 1 to 11, wherein irradiation in step B) is carried out with electromagnetic radiation having a wavelength of 500 nm or below, preferably 450 nm or below, more preferably in the range of 250 to 440 nm, even more preferably in the range of 300 to 430 nm.

13. The process according to any one of claims 1 to 12, wherein the reaction temperature range in step B) is from -30°C to 220° C, preferably from 200 to 220° C and even more preferably from 70 to 180° C.

14. A recycling process for vinyl polymers comprising at least the process according to any one of claims 1 to 13.

15. The use of chlorine -containing reagents for the depolymerization of vinyl polymers.

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