Pressure-Volume Behavior of PMMA-MMA Coexistence System as Polymerized at High Pressure

The pressure-volume (P-V) isotherms were measured for the poly(methy1 methacrylate) (PMMA)-methyl methacrylate (MMA) coexistence system polymerized by γ-ray irradiation at various pressures. The P-V isotherm of the coexistence system polymerized below 3000 kg/cm² was similar to that of the monomer. The specific volume of the coexistence system polymerized above 3000 kg/cm² hardly changes in the pressure range between 3000 kg/cm² and the polymerization pressure when measurements are made with successively decreasing or successively increasing pressures. The compressibility was of the order of 10^?6 (kg/cm²)^?1 in this pressure range. This indicated that the coexistence system polymerized above 3000 kg/cm² behaves like a solid in this pressure range. Above the polymerization pressure, the compressibility was of the order of 10^?5 (kg/cm²)^?1, indicating that the coexistence system behaves as liquid. We concluded that the solid-like behavior of the coexistence system polymerized above 3000 kg/cm² is caused by a strong interaction between as-polymerized polymer chains and monomer molecules due to propagation through monomer clusters having short-range order. The present results support that MMA is aligned in short-range order at suitable pressure and temperature as reported in the preceding paper.