Radiation-Induced Polymerization of Methyl Methacrylate at High Pressure

Radiation-induced polymerization of methyl methacrylate (MMA) was studied up to 7500 kg/cm² at 20°C. The rate of polymerization increased to 3000 kg/cm² with overall activation volume ΔV_pol? of -23.6 cm³/mole, and then the pressure dependence of the rate was very small in the pressure range between 3000 and 3700 kg/cm². The rate of polymerization increased again above 3700 kg/cm² up to the crystallization pressure of MMA (5500 kg/cm²) with ΔV_pol? of -13.7 cm³/ mole with increasing pressure. The volume contraction by polymerization decreased with increasing pressure up to 3000 kg/cm² but hardly decreased with increasing pressure above 3000 kg/cm². The stereoregulzarity (triad probability) of PMMA changed slightly at 3000 kg/cm; above 3000 kg/cm², syndiotactic addition decreased and heterotactic addition increased. Marked change in P-V isotherms of MMA, however, was not observed about 3000 kg/cm². We concluded from these facts that an alignment of monomer molecules, which does not cause large volume change, was realized about 3000 kg/cm². Polymerization proceeded above the crystallization pressure by long time irradiation, and isotactic addition increased clearly in the solid-state polymerization.