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.
The usual photochemical method and the rotating sector technique have been used to study the effect of conversion on the termination mechanism in the polymerization of methyl methacrylate. The strong rate acceleration, the extreme increase in kinetic chain lifetime and some decreases in the overall activation energy and the reaction order of chain termination have been detected with increasing conversion of the reaction system. These results are in good agreement with those reported on styrene in the first paper of this series and with the available data on this polymerization. These results have been discussed under several assumptions and confirmed to be due to a large change in the termination mechanism, i. e., from the activation-controlled termination of polymer radicals in the initial stages to the predominant diffusion-controlled termination in the later stages.
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