Melt crystallization of bisphenol A polycarbonate in PC/zinc sulfonated polystyrene ionomer blend

Date of Completion

January 2003

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

The effects of zinc sulfonated polystyrene ionomer (ZnSPS) on the melt crystallization of bisphenol A polycarbonate (PC) were investigated. Melt crystallization of pure PC is extremely slow due to its rigid chain. In the blend of PC and ZnSPS (PC-ZnSPS), the melt crystallization rate of PC can be enhanced. ^ DSC was used to study the crystallization kinetics of PC in PC-ZnSPS blend. The crystallization of PC at 190°C increased in both partially miscible and miscible blends with ZnSPS. For PC-ZnSPS blend with same PC composition as 80%, the crystallization rate was affected by the sulfonation level of ZnSPS. The induction time of crystallization for a partially miscible blend PC-ZnSPS9.98 (80/20) was 40 minutes, and the crystallization reaches 27% crystallinity within 14 hrs. The induction time for pure PC with the same thermal history was more than 24 hrs. The crystal structure of PC crystal formed in PC-ZnSPS blend was studied by WAXD, which showed no difference from the reported WAXD pattern for pure PC. Molecular weight change of PC was found during the thermal annealing of PC-ZnSPS blend at 190°C, but molecular weight alone cannot explain the change of crystallization rate of PC in PC-ZnSPS blend. Discussion was made to address the mechanisms that are responsible for the crystallization rate enhancement of PC in PC-ZnSPS blend. ^ In order to understand and elucidate the reason for the molecular weight change of PC in PC-ZnSPS blend and its effect on the crystallization of PC, TG, GPC and GC-MS were used to investigate the stability of PC-ZnSPS blend and mixtures of PC with sodium tosylate (NaTS), zinc tosylate (ZnTS) and sodium benzoate (NaBZ). ZnSPS, NaTS and ZnTS undergo desulfonation of the sulfonate group at temperatures above 350°C. The desulfonation process can destabilize PC and lower the maximum mass loss rate temperature of PC for more than 70°C. NaTS, ZnTS and NaBZ have quite different effect on the thermal stability of PC at temperatures below 250°C. NaBZ can significantly degrade PC both at 190°C and 250°C. PC does not show any molecular weight (M w) change in the presence of NaTS at 250°C and 190°C for up to 1hr and 16 hrs respectively. ZnTS can also cause Mw change of PC at 250°C and 190°C, but the changing of Mw of PC in the presence of ZnTS is less than that in the presence of NaBZ. The reason for the molecular weight change of PC in PC-ZnSPS blend can be explained based on Davis's ionic ester exchange reaction mechanism. ^

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