CRYSTALLIZATION AND MELTING OF SYSTEM ISOTACTIC POLYSTYRENE AND POLY(2,6-DIMETHYL PHENYLENE OXIDE)

From glass transition T//g measurements on isotactic polystyrene (IPS)-poly(2-6-dimethyl phenylene oxide) (PPO) blends, it was concluded that thoroughly annealed, freeze-dried samples, or samples evaporated from solution at high temperature, are homogeneous. Without annealing, the freeze-dried blends show two to three T//g's characteristic of the presence of different phases. The overall crystallization rate of these samples is much higher than that observed with annealed samples. The presence of dissolved PPO in annealed samples reduces the overall crystallization rate and the spherulitic growth rate, compared to IPS. The melting behavior of the blends is influenced by the extent of mixing of both polymers. Without annealing, isothermally crystallized, free-dried blends show the same melting behavior as IPS (i. e. , multiple melting). In homogeneous annealed samples the rate of reorganization is strongly reduced and multiple melting only occurs at low scanning rate (e. g. , 1 degree C/min). This behavior is influenced by the crystallization temperature and by the composition of the blends.