Miscibility with positive deviation in Tg-composition relationship in blends of poly(2-vinyl pyridine)-block-poly(ethylene oxide) and poly(p-vinyl phenol)

Phase behavior and miscibility with positive deviation from linear T_g-composition relationship in a copolymer/homopolymer blend system, poly(2-vinyl pyridine)-block-poly(ethylene oxide) (P2VP-b-PEO)/poly(p-vinyl phenol) (PVPh), were investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR), optical microscopy (OM), and scanning electron microscopy (SEM). Optical and electron microscopy results as well as NMR proton spin-lattice relaxation times in laboratory frame () all confirmed the miscibility as judged by the T_g criterion using DSC. In comparison to the literature result on a homopolymer/homopolymer blend of P2VP/PVPh, fitting with the Kwei equation on the T_g-composition relationship for the block-copolymer/homopolymer blend of P2VP-b-PEO/PVPh blend system yielded a smaller q value (q = 120) for P2VP-b-PEO/PVPh than that for P2VP/PVPh blend (q = 160). The FT-IR and ¹³C NMR results revealed hydrogen-bonding interactions between the pendant pyridine group of P2VP-b-PEO and phenol unit in PVPh, which is responsible for the noted positive deviation of the T_g-composition relationship. Comparison of the shifts of hydroxyl IR absorbance band, reflecting the average strength of H-bonding, indicates a decreasing order of P2VP/PVPh > P2VP-b-PEO/PVPh > PEO/PVPh blends. The PEO block in the copolymer segment tends to defray the interaction strength in the P2VP-b-PEO/PVPh blends because of relative weaker interaction between PEO and PVPh than that between P2VP and PVPh pairs. A comparative ternary (P2VP/PEO)/PVPh blend was also studied as the controlling experiments for comparison to the P2VP-b-PEO/PVPh blend. The thermal behavior and interaction strength in (P2VP/PEO)/PVPh ternary blends are discussed with those in the P2VP-b-PEO/PVPh copolymer/homopolymer blend.