Crystallization behavior of single or pauci chain aggregates of isotactic polystyrene

Abstract

Single and pauci chain aggregates of isotactic polystyrene (i-PS) were prepared by the freeze-drying process from dilute solutions with the concentration from 1?10^-3 to 2?10^-5 g/mL. It was found by DSC measurements that the melting point of samples gradually shifted to lower temperatures with the decrease of the solution concentration used for sample preparation. As a result, the lamella thickness of bulk samples and the samples prepared by the freeze-drying process from a solution of 2?10^-5 g/mL was 19.3 and 12.6 nm, respectively. At 468.3 K the half crystallization time (t_1/2) of samples freeze-dried from a solution of 1?10^-4 g/mL was about 36 s, which was merely one tenth of that of the bulk sample. In addition, the growth rate of spherulite (dr/dt) of samples prepared from a solution of 2?10^-5 g/mL was faster than that of the bulk sample annealed at 478.3 K. All these results should be attributed to the fewer entanglements in samples prepared by freeze-drying process from dilute solutions, and presented clear evidence for the influence of chain entanglements on the crystallization behavior of polymers.

Keywords

isotactic polystyrene, single chain aggregates, pauci chain aggregates, crystallization