Influence of isomer ratio and ring substituents in decomposition activation energies of α,α,α′,α′‐tetrasubstituted dibenzyls

Abstract

Diethyl-2,3-dicyano-2,3-di-(X-substituted phenyl) succinates (X ϭ p-OCH 3 , p-CH 3 , p-Cl, H, p-NO 2 ) can initiate the free-radical polymerization of styrene. The decomposition rate constant and activation energy were measured by means of a dilatometer, and the results showed that they were strongly dependent on the ratio of meso-and dl-isomers in the polysubstituted dibenzyl compounds and the properties of the ring substituents. On the other hand, it was found that the polystyrenes, which were obtained by initiation with hydrogen, had a much larger average molecular weight than that with p-OCH 3 and p-CH 3 . The experimental phenomena were correlated with the structure of the radical resulting from hydrogen.

Thermolysis kinetics of diethyl 2,3‐dicyano‐2,3‐di(p‐substituted phenyl)succinates

“…The radical intermediates derived from the central C–C bond homolysis were confirmed by the well‐resolved electron spin resonance spectrum . The formation of radical intermediates is further supported by the fact that diethyl 2,3‐dicyano‐2,3‐di( p ‐substituted phenyl)succinates can all be used as radical initiators for various alkene polymerizations …”

“…These results are in sharp contrast to the negligible effects of reaction temperature and p ‐substituents on the dl / meso isomerization equilibrium constants . It is worth noting that the thermolysis rate constants (Table ) are all much larger than the rate (10 –4 min –1 ) of radical formation required for efficient polymerization initiators, suggesting that these hexasubstituted ethanes can be used as polymerization initiators …”

“…Although the central C–C bond lengths are longer (~1.60 Å) than the standard (1.54 Å), the dl and meso diastereomers are both stable, indicating that the corresponding homolysis into diradicals is negligible at room temperature. However, these dl and meso diastereomers have been demonstrated as excellent polymerization initiators at ~100 °C for various alkene monomers such as styrene, acrylonitrile, methyl mathacrylate, etc …”