Ultradrawing of polystyrene by solid‐state coextrusion: Shear‐induced crystallization in isotactic polystyrene

Polystyrene with a 60% isotactic dyad content (iPS) was subjected to two‐stage solid‐state coextrusion at 124 and 160°C. It was shown that only shear‐induced crystallization occurred with the amount of crystallinity strongly dependent on draw ratio. The steep increase in crystallinity from 0 to 29% is accompanied by a marked increase in the absolute total birefringence from 0 to 30 × 10 −3 and the tensile properties, from 2.5 GPa to 4.5 GPa, giving strong evidence for the necessity of a crystalline phase to achieve higher tensile moduli. Wide‐angle X‐ray scattering showed a higher crystal orientation for the extrudate produced at 124°C than for the one produced at 160°C. Thermal shrinkage experiments support a partial dissipation of orientation after extrusion at 160°C and on reextrusion in general. Electron microscopy revealed a fibrous nature for the solid‐state coextrudates produced at both temperatures.