Miscibility with asymmetrical interactions in blends of two carbonyl-containing polymers: Poly(vinyl acetate) with aliphatic polyesters

Phase behavior, miscibility, or immiscibility in blends of two polymers with carbonyl groups, PVAc and homologous polyesters of different CH2/CO ratios, were examined using DSC, OM and SEM. Polyesters used in this study included PES, PEA, PPA, and PBA. PVAc/polyester blends were found to be immiscible with distinctly a two-phase morphology when the polyesters' structural CH2/CO ratios are lower than 3 or higher than 4; whereas miscibility is seen in three blend systems: PVAc/PEA (CH2/CO=3.0), PVAc/PPA (CH2/CO=3.5), and PVAc/PBA (CH2/CO=4.0). Asymmetry in the T-g-composition relationships is seen in all three miscible blend systems. Such non-specific, weak and asymmetrical interactions, though sufficient to maintain borderline miscibility in the blends, may be partially responsible for leading to the noted asymmetry in the T-g-composition relation of the blends. Mechanism and origin of this phenomenon of asymmetry in T-g-composition relationships in some blends may be still puzzling. Strictly speaking, the non-equilibrium phenomenon of glass transition may not be ideal for evaluating the strength of intermolecular interactions in blends. Future perfection on more suitable approaches may yet be needed.