Polymethacrylic thermal degradation

It may be noted here that the thermal degradation of polyacrylates does not follow the same pattern as that of the polymethacrylates. None of the polyacrylates gives appreciable yields of monomer or olefin the principal products are polymeric fragments which arise by chain scission accompanied by transfer of tertiary hydrogen atoms. 

At high temperatures the image of photodegradation changes completely because additional reactions are involved in the thermal degradation of a polymer [1319]. Many papers have been devoted to the study of photothermal degradation of polyethylene [148,1289], polypropylene [822], poly(ethylene-co-carbon monoxide) [871, 917], polyacrylates and polymethacrylates [821, 829], poly(acrylate-co-methacrylate) [828, 831], poly(vinyl chloride) [311, 702, 768, 891,1097,1319,1792] polystyrene [1491], natural rubber [14] and poly(ether sulphone) [1265]. 

Thermal depolymerisation products are monomers (or co-monomers in the case of copolymer degradation), i.e., polymethacrylates and PS degrade by depolymerisation mostly - and monomeric-dimeric and trimeric nnits (methacrylates or styrenes, respectively), split off from the system. Both are snspected of cansing cancer. For PS, monomer yield of thermal depolymerisation can be as high as 40%, while PMMA can decompose to the monomers completely above 300 C [79, 80]. 

Although several other methacrylate ester polymers resemble PMMA in degrading thermally to give 100% monomer, this behaviour is by no means general for this class of polymers and some polymethacrylates, in contrast, give very little monomer. 

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