Some Nonradical Degradation Mechanisms

Although the majority of polymers degrade thermally or photochemically by a free-radical process, there are a few examples vhere covalent bond scission occurs by electron transfer around a six-membered transition state. Thermal degradation of poly(ethylene terephthalate) [Eq. (20)] and side group cleavage in poly(methyl acrylate) and poly(tert-butyl methacrylate) are some examples vhere j5-scission of the alkyl-oxygen bond takes place from a cyclic transition state vithout free-radical formation [4]. 

Cyclization of side chains may also occur vithout bond scission as in polyacrylonitrile (see Section 15.4.6.3). 

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