Dynamics study of free volume properties of SMA/SMMA blends by PAL method

Miscibility of poly(styrene-co-maleic anhydride) (containing 7 wt% maleic anhydride)/poly(styrene-co-methyl methacrylate) (containing 40 wt% styrene) blends were previously studied. It was obtained that SMA70 (containing 70 wt% of SMA in SMA/SMMA blends) is miscible in molecular level but SMA20 is not. In this paper, the two blends selected were used to investigate the temperature dependence of free volume parameters. It showed there are different deviations of free volume parameters in SMA20 and SMA70, and it was interesting that temperature dependence of ortho-positronium lifetime τ3 of the SMA20 mixture exhibits two breaks in the range temperature from 90 °C to 120 °C, which revealed that the mixture has two glass transition ranges. Also, ortho-positronium lifetime τ3 of the SMA20 mixture is nearly constant in the temperature range from 130 °C to 160 °C. These indicated that SMA20 blend is phase-separated in room temperature and become miscible above 130 °C, which may be due to steric hindrance effect of phenyl rings of SMMA and SMA. From the deviation of o-Ps lifetimes of SMA70, the single glass transition temperature of SMA70 blend was shown. Combining the previous study, it was further concluded that PAL method seems to be a powerful method to detect in situ phase behavior of immiscible polymer blends and glass transition of miscible polymer blends.