Tetraphenylethanes as initiators of radical polymerization. II. Dead-end polymerization of styrene
The polymerization of styrene with the use of tetraphenylethanes as initiators is an example of dead-end polymerization. At higher concentrations of the initiator, the chain growth is terminated exclusively by their reaction with primary radicals. Thus, the polymerization rate (vbr) depends only on monomer concentration: vbr = k1·[M]2 . During polymerization the initiator concentration decreases, thus decreasing the contribution of primary radicals in the termination reaction — this results in a Continuous change in the reaction order, namely
— in relation to the initiator 0.25 → 0
— in relation to the monomer 1.5 → 2.
In contradistinction to analogous telechelic oligomers of methyl methacrylate, oligostyrenes are not able to initiate radical polymerizations below 100°C. The end C-C bond in oligostyrenes can be made more labile by the introduction of an additional substituent. The thus-prepared telechelic oligomers of a-methylstyrene appeared to be effective initiators of radical polymerizations at temperatures over 50°C.
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