Pressure effect on the kinetics of polymerization I : bulk polymerization of vinyl chloride, propylene and butadiene

Abstract

The bulk polymerization of vinyl chloride with benzoyl peroxide as the initiator, was carried out at 40°to 70℃ under high pressures in the range of 1.170 to 3, 900kg/cm^2. These results were considered in comparison with those of radical polymerization of propylene (with benzoyl peroxide as the initiator at 80°to 100℃, 2, 800 to 4, 000kg/cm^2) and thermal polymerization of butadiene (at 50°to 95℃, 1, 100 to 5, 000kg/cm^2), from the kinetic viewpoint. In all cases, it was observed that the polymerization reaction was not preceded by any induction periods, and the polymer yields increased linearly with the reaction time throughout the comparatively long runs. The rate of polymerization was accelerated by increasing pressure and temperature. From the apparent initial rate. the activation energies (E), the activation volumes (ΔV≠) and the activation entropies (ΔS≠) were calculated, and the following values were obtained; i) for vinyl chloride, E=20.6 to 24.0 kcal/mole, ΔV≠=-4.6 to -10.4cm^3/mole and ΔS≠=-15.1 to -2.3 e.u., ii) for propylene, E=11.9 to 12.3 kcal/mole, ΔV≠=-9.0 to -12.7 cm^3/mole and ΔS≠=-46.4 to -42.0 e.u., iii) for butadiene, E=15.1 to 19.2 kcal/mole, ΔV≠=-8.8 to -17.2 cm^3/mole and ΔS≠=-38.0 to -24.3 e.u. The activation entropies and activation energies were increased by increasing pressure, but the activation volumes showed negative values. Then, the accelerating effect of pressure on the polymerization reaction is entirely ascribed to the increase in the activation entropy which overcomes the rise of activation energy. The latter is considered to retard the rate of the reaction. From the X-ray diffraction and infrared absorption analyses, following subjects were concluded. 1. The polyvinyl chloride obtained was not different from the ordinary polyvinyl chloride, but the degree of polymerization was increased by increasing pressure, i.e., P^^-=1, 470 to 1, 900 at 50℃. 2. The polypropylene obtained was atactic polypropylene. The degree of polymerization was very low and was unaffected by pressure, i.e., P^^-=14 to 65 at 80°to 100℃. 3. The polybutadiene obtained was insoluble in the ordinary solvents of rubbers, and was a crosslinked elastic polymer.