Microhardness of condensation polymers and copolymers. 2. Poly(ester ether carbonate) thermoplastic terpolymers

Abstract

The number of phases, transition temperatures, and microhardness of a series of poly(ester ether carbonate) (PEEC) multiblock terpolymers with poly(butylene terephthalate) (PBT) hard segments have been investigated as a function of ether/carbonate (EC) soft-segment composition at constant PBT content. The polymerization degree of PBT and the intrinsic viscosity of the terpolymers were determined by viscosimetry. The degree of crystal-Unity, long spacing, glass transitions Tg , and melting temperature were derived by means of x-ray diffraction, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) measurements. Surface mechanical properties were studied by microindentation tests. It was found that the terpolymer consists of two amorphous (EC and PBT) phases and one crystalline (PBT) phase. The Tg value of PBT does not depend on the chemical composition of the soft segments, in the contrast to the Tg of the soft-segment amorphous phase. Introduction of polycarbonate moities in the soft segments induces an increase of Tg by 50°C without formation of an additional (third) amorphous phase. The reduced crystallizability of PBT hard segments (by a factor of 3) is explained by this decrease of flexibility of the soft segments, which also causes a twofold reduction in the microhardness values. The dominating contribution of crystallinity to the microhardness is shown. However, the much lower measured overall microhardness in contrast to the one calculated by means of the additive law is explained by the plasticizing effect of the soft amorphous phase. This assumption is in agreement with the structure model derived from the small-angle x-ray (SAXS) and wide-angle x-ray (WAXS) data.