Phase Behavior of Poly(methyl methacrylate)/Poly(vinylidene fluoride) Blends in the Presence of High‐Pressure Carbon Dioxide

Abstract

Abstract Previous efforts have demonstrated that high‐pressure CO 2 can markedly influence the phase behavior of amorphous polymer blends. In this work, we examine the effect of high‐pressure CO 2 on the miscibility of blends composed of glassy poly(methyl methacrylate) (PMMA) and semicrystalline poly(vinylidene fluoride) (PVDF). Blends of this type are known to exhibit lower critical solution temperature (LCST) behavior with partial miscibility up to ≈50–60 wt.‐% PVDF at ambient conditions. Two miscible PMMA/PVDF blends have been systematically exposed to high‐pressure CO 2 at 35 °C and pressures below and above the critical pressure. Small‐angle X‐ray scattering reveals that the scattering intensity at high scattering angles shows little dependence on pressure at low CO 2 pressures, but increases substantially at relatively high CO 2 pressures. Transmission electron microscopy and differential scanning calorimetry analyses confirm that the blends are initially quasi‐homogeneous with diffuse PVDF‐rich dispersions and a single glass transition temperature. After exposure to relatively high CO 2 pressures, however, the PVDF is found to crystallize within the PMMA‐rich matrix. Thermal recycling of these blends promotes homogenization, indicating that such CO 2 ‐altered phase behavior is reversible. SAXS patterns acquired from the 69/31 w/w PMMA/PVDF blend. magnified image SAXS patterns acquired from the 69/31 w/w PMMA/PVDF blend.