Termination Reaction in Vinyl Polymerization: Preparation of Block Copolymers

Abstract

THE nature of the termination reaction in vinyl polymerization, that is, the question of disproportionation or combination of polymeric free radicals, has been the subject of controversy. A number of methods have been used for distinguishing between the various possibilities^1–4; these depend on relations between degrees of polymerization measured by osmotic pressure and end-group analysis, or on relations between rate and molecular weight data. In all these cases the extremes of 100 per cent disproportionation of radicals and 100 per cent combination give rise only to a difference of a factor of two in the appropriate quantity which is compared with experiment. These methods have been applied to comparatively few monomers, and results obtained by different groups of workers have not always been in agreement^3,4. We therefore thought it worth while to attempt to devise an independent method of general application which would be more sensitive in its distinction between combination and disproportionation. We now wish to describe briefly the method which has been developed and its application to four vinyl monomers.