Glass transition behavior and miscibility in blends of poly(vinyl p-phenol) with two homologous aliphatic polyesters

New miscible blend systems comprised of poly(4-vinyl phenol) (PVPh) and a homologous series of polyesters of different CH₂/CO ratios (from 4.5 to 7) was discovered. Miscibility has been confirmed using differential scanning calorimetry, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The PVPh/polyesters blends investigated exhibited a single composition-dependent glass transition and homogeneous phase morphology, and they similarly exhibited a cusp in the T_g-composition relationships. This work further extended the range of aliphatic polyesters that are known to be miscible with PVPh. The Flory-Huggins interaction parameter (χ₁₂) or energy density (B) obtained from analysis of melting point depression for PVPh/PEAz and PVPh/PHS blends are of negative values. More interestingly, the specific interactions in the PVPh/polyester blends change with the corresponding different structures in the polyester component. For the PVPh/PHS blend whose polyester constituent possesses a lower carbonyl density in the main chain (average CH₂/CO ratio=7), the energy density B was found to be -1.17 cal cm^-3. This value is significantly lower than those for either the PVPh/PEAz (CH₂/CO=4.5) blend system (B=-7.72 cal cm^-3). Miscibility, specific interactions, and peculiar T _g-composition relationships in the blends of PVPh with selected homologous polyesters are discussed.