Miscibility studies of high Tg polyester and polycarbonate blends

Abstract

Differential scanning calorimetry (d.s.c.) has been applied to characterize the miscibility of blends of a high T g polyester, synthesized by condensation polymerization from 4,4′-(2-norbornylidene)diphenol and terephthalic acid/azelaic acid in a 60 40 molar ratio (this polyester will be denoted T(40)C-GJ), with bisphenol-A polycarbonate. The theoretical development to determine the Flory-Huggins interaction parameter (χ) of phase-separated polymer blends from their phase compositions is described. The glass transition temperature ( T g) of a miscible blend of T(40)C-GJ and a low molecular weight polycarbonate (Lexan) can be accurately described by both the Gordon-Taylor equation with k = 1.7 and the Couchman equation. These equations were used to determine the phase compositions of a phase-separated blend of T(40)C-GJ and a high molecular weight polycarbonate (Makrolon) from the T g data. The χ values for these blends are in the range (8.4–9.9) × 10 −3 and are slightly composition dependent. The miscibility of these blends can be quantitatively understood in terms of the χ results from the d.s.c. measurements. The morphology observed by transmission electron microscopy for 50 50 wt% blends of T(40)C-GJ and polycarbonate is consistent with the d.s.c. results.