The influence of chain transfer agents on rate of polymerization in the heterogeneous and homogeneous polymerization of vinyl chloride

Abstract

Abstract The addition of small amounts of effective chain transfer agents such as carbon tetrabromide and dodecyl mercaptane to the azo‐iso‐butyronitrile‐initiated polymerization of vinyl chloride in 1.2‐dichloroethane leads to a marked increase in the rate of polymerization which, although lesser than in the heterogeneous bulk polymerization of vinyl chloride, amounts to approximately 20% in this completely homogeneous system. At higher transfer agent concentrations due to the slightly retarding action of the transfer agent a decrease in rate is to be observed so that maximum rates are obtained with 3ċ10 −4 moles of transfer agent per mole of monomer. As in the heterogeneous bulk polymerization the increase of rate is explained by a transformation of the less active radicals formed by chain transfer to monomer into the more active radicals derived from the chain transfer agent, leading to an increase in kinetic chain length. The influence of the chain transfer agent on the heterogeneous and homogeneous polymerization of vinyl chloride is compared and a kinetic scheme, which is representative for both cases, is established and discussed in detail.