Glass transition behavior of polypropylene/polystyrene/styrene-ethylene-propylene block copolymer blends

Summary The glass transition behavior of ternary blends of polypropylene (PP), polystyrene (PS) and styrene-ethylene-propylene-styrene block copolymer (SEPS) was investigated. The blends were prepared by an internal mixer, and their dynamic mechanical properties and morphology were measured. The blends showed phase inversion at around 75wt% PS composition. The glass transition temperature (T_g) of the PP phase shifted to lower temperature as the PS contents were increased in PP/PS binary blends, probably due to the mismatch of thermal expansion coefficients between two components. As the SEPS copolymer contents were increased, the T_g's of the PP phase in the blends increased. In particular, the large increase in T_g of the PP phase was observed in the PP/PS (25/75) blends where the phase inversion takes place. Received: 2 February 1998/Revised version: 24 March 1998/Accepted: 13 April 1998