Reactive blending of bisphenol-A polycarbonate with isosorbide-based polycarbonates: Effect of chain flexibility and compatibility

Abstract

In this study the effect of flexible 1,4-cyclohexanedimethanol (CHDM) units on the reactive blending of poly(isosorbide-co-CHDM carbonate) (IcC-PC) with bisphenol-A polycarbonate (BPA-PC) was investigated and the contributions of chain flexibility and compatibility to transesterification were clarified. FTIR analysis revealed the presence of specific interactions between the CHDM segments of IcC-PC and the carbonyl group and phenyl rings of BPA-PC, leading to thermodynamic miscibility of the polymer blends when the CHDM content was higher than 50 mol% in IcC-PC. Addition of organotin catalysts during melt blending triggered transesterification between IcC-PC and BPA-PC, transforming the opaque blends into transparent alloys with a single Tg when the transesterification ratio reached a critical value. It was found that the reactivity of isosorbide (ISB) segments was higher than that of CHDM segments. The increase in the CHDM/ISB ratio first accelerated and then slowed down the transesterification, demonstrating that, despite of the low reactivity of the CHDM segments, the enhanced chain flexibility and compatibility were effective for promoting transesterification. Anyway, copolymerization of CHDM with ISB improved the compatibility of IcC-PC with BPA-PC, reduced the critical transesterification ratio for transparency, and remarkably shortened the blending time essential for the large-scale fabrication of transparent ISB-based polycarbonate alloys by twin-screw reactive extrusion.