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The rmal Polymerization

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  ص106-107

2026-01-13

426

The rmal Polymerization

A few monomers, such as styrene and methyl methacrylate, will, after careful purification and presumably free from all impurities, polymerize at elevated temperatures. It is supposed that some ring-substituted styrenes act similarly. The rates of such thermal self-initiated polymerizations are slower than those carried out with the aid of initiators. Styrene, for instance, polymerizes only at a rate of 0.1% per hour at 60C and only 14% at 127C. The rate of thermal polymerization of methyl methacrylate is only about 1% of the rate for styrene [163, 164]. Several mechanisms of initiation were proposed earlier. The subject was reviewed critically [165]. More recently, the initiation mechanism for styrene polymerization has been shown by ultraviolet spectroscopy to consist of an initial formation of a Diels–Alder dimer. The dimer is believed to subsequently transfer a hydrogen to a styrene molecule and as in doing so form a free radical [166]:

Thermal polymerization of methyl methacrylate, on the other hand, appears to proceed through an initial dimerization into a diradical [167]. This is followed by a hydrogen abstraction from any available source in the reaction mixture.