Influence of isomer ratio and ring substituents in decomposition activation energies of alpha,alpha,alpha ',alpha '-tetrasubstituted dibenzyls

Diethyl-2,3-dicyano-2,3-di-(X-substitute phenyl)succinates(X = p-OCH3, p-CH 3, p-Cl, H, p-NO,) can initiate the free-radical polymerization of styrene. The decomposition rate constant and activation energy were measured by mea ns of a dilatometer, and the results showed that they were strongly depende nt on the ratio of meso- and dl-isomers in the polysubstituted dibenzyl com pounds and the properties of the ring substituents. On the other hand, it w as found that the polystyrenes, which were obtained by initiation with hydr ogen, had a much larger average molecular weight than that with p-OCH3 and p-CH3. The experimental phenomena were correlated with the structure of the radical resulting from hydrogen. (C) 2001 John Wiley & Sons, Inc.