Growth of spherulites with positive and negative birefringence in syndiotactic polystyrene/poly(vinyl methyl ether) blend films

The morphology and the spherulite radial growth rate of syndiotactic polystyrene (sPS) in melt crystallized samples are strongly altered by blending with poly(vinyl methyl ether) (PVME). In particular, for the plain sPS two types of spherulite are observed. Both types of spherulite have positive birefringence and the same radial growth rate. In the blend film another type of spherulite is also present having negative birefringence. The negative and positive spherulites are distinct in their crystallization kinetics. It has been found that for the same crystallization temperature, T(c), and composition, the positive spherulites grow faster than the negative spherulites. Comparing the values of the growth rate of positive sPS spherulites, grown from sPS/PVME blends, with that of pure sPS, resulted in G being higher for blends than for pure sPS at a given T(c). This result, already obtained for isotactic polystyrene/PVME blends (iPS/PVME), was related to the increase in mobility of the crystallizable molecules in the melt following addition of PVME.