The Effect of Conversion on the Mechanism of Vinyl Polymerization. I Styrene

Abstract

Abstract The polymerization of pure styrene has been studied photochemically near room temperatures and in the range 0 to about 70 % conversion, and the following results have been obtained. With increasing conversion; (1) both the direct photo-polymerization and the thermal polymerization are accelerated strongly, (2) the over-all activation energies in both polymerizations decreases, (3) the lifetime of kinetic chains increased steadily and the photochemical initial and after effects are easily observed dilatometrically over 30 % conversion. Also (4) the reaction order of chain termination is 2 in the range 0 to about 40 % conversion, but it becomes less than 2 at the conversions over 60 %. Thus these results have been discussed on several assumptions and it has been concluded that they are attributed to a considerable change in the mechanism of radical termination with increasing conversion of the reaction system, i.e., the change from an activation-controlled termination to a diffusion-controlled one.