Photo‐sensitized polymerization of styrene under high pressure

The polymerization of styrene, photosensitized by azocyclohexane‐1,1′‐dinitrile, was studied at 30°C over a pressure range of 1 to ca. 1000 bar. The average lifetimes of the growing polymer chains were determined by the rotating‐sector method. By measuring the effect of pressure on the individual reactions of styrene polymerization, the activation volumes for the propagation and the termination were obtained as −17,9 cm3/mol and 13,1 cm3/mol, respectively. The overall activation volume was also measured as −17,9 cm3/mol and was nearly equal to that calculated from the individual activation volumes (−17,8 cm3/mol). The propagation rate constant increases exponentially with pressure, whereas the termination rate constant decreases rapidly up to 500 bar and then decreases slowly as the pressure increases further.