Polymerisation at high pressures near the liquid-solid phase boundary

The melting point-pressure relationship for three disubstituted ethylene compounds has been determined tc within 40 atmospheres. The melting pressures at 60° C. of these substances are: ethyl cinnamate, 2900 atmos.; diethyl fumarate, 3680 atmos.; and a-methylstyrene, 3700 atmos. The free radical polymerisations of ethyl cinnamate and diethyl fumarate have been studied in detail, particularly in the region of the freezing pressures. Previous research on a-methylstyrene polymerisation was verified in part, but the reported value of the freezing pressure of this compound at 60° C. was found to be in error. Some physical properties of polymers, especially molecular weights, have been determined and the pressure effect on these properties is discussed. A few experiments with ethyl crotonate are recorded. The overall volume of activation, AV*, has been determined for each reaction, the values being: ethyl cinnamate, - 54.0 cc./mole; diethyl fumarate, -14.7 cc./mole; and a-methylstyrene, -18.4 cc./mole. In the case of ethyl cinnamate, the reaction is complicated by a phase separation which accounts for the very high value of HIV* observed. The molecular weights were found to behave sigmoidally with pressure for all three compounds. This behaviour with a-methylstyrene is in disagreement with a previous study, but closely follows the behaviour of styrene. There was no discontinuity in the molecular weights of these three polymers in the vicinity of the liquid-solid phase boundary.