Effect of pressure on phase behavior in polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(o‐fluorostyrene‐co‐p‐fluorostyrene) copolymers

摘要

AbstractThe effect of pressure on miscibility and phase separation in blends of random copolymers ofortho‐ andpara‐fluorostyrene, P(o‐FS‐co‐p‐FS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide), PPO, has been studied by differential thermal analysis (DTA) at pressures up to 300 MPa. At 200 MPa the copolymers containing from 10 to 38 molp‐FS are miscible with PPO below 230°C using the customary criterion of a single calorimetric glass transition temperature (Tg). Each blend undergoes phase separation upon annealing at higher temperatures at both atmospheric and elevated pressures indicating the presence of a lower critical solution temperature (LCST). When the phase behaviors of the 50/50 wt blends are examined as a function of temperature and copolymer composition, a symmetric miscibility “window” can be observed in the resulting temperature‐composition diagram with a maximum at about 22 molp‐FS. In a complementary set of experiments, the pressure dependence of the phase boundary for the blend of PPO and P(o‐FS‐co‐p‐FS) in which the copolymer contained 29 molp‐FS was studied. The temperature minimum of the phase boundary is at about 50 wt PPO and is independent of pressure. The consolute temperature,Tc, increases at about 0.10°C/MPa up to 200 MPa and then becomes independent of pressure to reach an asymptotic value at around 270°C. Similar behavior is also observed for blends in which the copolymer composition contains either 16 or 23 molp‐FS. In these blends the decrease ofdTc/dP at higher pressures may indicate that the negative volume of mixing approaches zero above 200 MPa. This study shows therefore, that pressure no longer plays a role i