The percolation limits for two-phase blends of PMMA and copolymers of styrene and MMA

Abstract

Phase separation and phase structure growth were studied, in the temperature range 150–220°C, in blends of poly(methyl methacrylate) (PMMA) and random copolymers of styrene and methyl methacrylate [P(S x MMA 1− x )] with x ≧ 0.4. Blends with 0.4 ≦ x < 0.6 are homogeneous at lower temperatures. One-phase films of these blends were cast at room temperature from solution. Granules of all blends with 0.4 ≦ x ≦ 1 were made by extrusion at 180†C. They had a fine two-phase morphology. Isothermal structure evolution was studied with both types of blends. The types of morphology and the structure growth rates were investigated, particularly in late stages where growth proceeds under steady-state conditions. The percolation limits between domain-matrix and cocontinuous morphologies were determined as a function of the incompatibility, χ χ c , which strongly increases with x in the blend series. The percolation range proved to be similar to the spinodal range at low χ χ c , but not at high χ χ c , where cocontinuous morphologies are found in a narrow range only.