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

The number of phases, transition temperatures, and microhardness of a series of poly(ester ether carbonate) (PEEC) multiblock terpolymers with poly(butylene terephthalate) (PET) hard segments have been investigated as a function of ether/carbonate (EC) soft-segment composition at constant PET content. The polymerization degree of PET and the intrinsic viscosity of the terpolymers were determined by viscosimetry. The degree of crystallinity, long spacing, glass transitions T-g, 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 PET) phases and one crystalline (PET) phase. The T-g value of PET does not depend on the chemical composition of the soft segments, in the contrast to the T-g of the soft-segment amorphous phase. Introduction of polycarbonate moities in the soft segments induces an increase of T-g by 50 degrees C without formation of an additional (third) amorphous phase. The reduced crystallizability of PET 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.