Abstract
The thermal degradation of poly(methyl methacrylate) (PMMA) without chain-end double bonds was studied at 140–180°C by a photoinitiation method involving benzophenone derivatives. The temperature range of main-chain scission can be lowered from 270–330°C, the usual thermal degradation condition for anionically prepared poly(methyl methacrylate), to the 140–180°C temperature range of the photoinitiated case. The formation of a PMMA on-chain radical by hydrogen abstraction by a triplet benzophenone derivative with low initiator efficiency (f=0.02–0.03) is followed by its β-scission and depolymerization with a zip length of 790–3200 at 140–180°C for PMMA with Mn0=8.4×105. A first-order termination mechanism for the polymer radical is suggested, based on the irradiation intensity dependence of the chain scission. The rate of weight loss during thermal degradation is independent of the molecular weight of PMMA, but the rate of main-chain scission increases with decreasing molecular weight, suggesting that a terminal alkyl radical produced by complete depolymerization undergoes chain transfer more easily than other radicals existing during the depropagation process. Thus, the terminal alkyl radical is supposed to abstract hydrogen from polymer chain and regenerate polymer on-chain radical and successive β-scission.
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Mita, I., Obata, K. & Horie, K. Photoinitiated Thermal Degradation of Polymers II. Poly(methyl methacrylate). Polym J 22, 397–410 (1990). https://doi.org/10.1295/polymj.22.397
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DOI: https://doi.org/10.1295/polymj.22.397