Shear-induced crystallization and rheological behavior of syndiotactic polystyrene

We studied the correlation between shear-induced crystallization and rheological behavior of syndiotactic polystyrene. It was found that after applying a steady shear flow around the nominal melting temperature (Tm = 270 °C), crystal growth rate was accelerated compared with the quiescent state and a morphology of oriented lamellae (kebabs) was observed. On the other hand, no obvious morphological change was observed when applying a shear flow with relatively slow shear rate. We discussed a possibility that the difference of crystal growth rate and morphology could be attributed to the competition between shear rate and relaxation time such as reptation time. Our rheological results suggested that when the imposed shear rate is close to the reciprocal of reptation time, oriented lamellae (kebabs) are observed but extended-chain crystals (shishs) cannot be formed since the chain segments between adjacent entanglements remain unstretched.