Abstract
AbstractThe free‐radical polymerization of methyl methacrylate at low temperatures has been studied in a series of solvents of differing solvent power and ability to form weak complexes with monomer. In every case the polymer was predominantly syndiotactic, which suggests that monomer association or complex formation are not important stereoregulating factors, and that the treatment of the propagation reaction as two concurrent addition reactions between monomer and a free propagating species is justified. The polymerization has been studied over the temperature range −20 to −60°C. with ethylsilver as initiator. Over these temperatures the overall rate law is Rp = K[M]3/2 [Ag]1/2 where K, a composite constant, can be expressed as 1.7 exp{ −5100/RT} 1. mole−1 sec.−1. The polymerization proceeds by a free radical mechanism, the initiation step appearing to be the decomposition of a ethylsilver–monomer complex to form metallic silver, and a free radical capable of initiating polymerization. The first‐order rate constant for this decomposition in ethyl acetate as solvent has the value 1.5 × 102 exp{−6600/RT} sec.−1. The molecular weights of the polymers formed are higher than would be predicted by extrapolation of data from higher temperatures, and also indicate that transfer reactions to catalyst components are negligible in the range of initiator concentrations studied.
Published Version
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