Strong intermolecular hydrogen bonding is capable of suppressing concentration fluctuations and coupling segmental relaxations in polymer blends whose components exhibit a large difference in their respective Tg's (ΔTg). In this paper we report on our dielectric study of blends of poly(4-vinylphenol) [PVPh] with poly(vinyl acetate) [PVAc] and a random ethylene-vinyl acetate copolymer [EVA70]. Dielectric spectra were collected over a broad frequency range (0.01 Hz-10 MHz) for blends with PVPh concentrations ranging from 10% to 40%. Although both blends have large ΔTg's (i.e., 116 K for PVPh/PVAc and 173 K for PVPh/EVA70), a single segmental relaxation was observed in most samples. This is attributed to the strong coupling arising from intermolecular hydrogen bonding. The fragility increases modestly with PVPh concentration as a result of enhanced intermolecular coupling. The effect of hydrogen bonding on fragility is discussed by considering hydrogen bond strength, its change with temperature, and competition between inter- and intramolecular association. Concentration fluctuations in PVPh/PVAc blends are insignificant, although PVPh/EVA70 blends show a broad relaxation time distribution as a result of their very large ΔTg and the distribution of intermolecular hydrogen bonds. Some independently relaxing segments may involve only one intermolecular hydrogen bond, whereas others include two or more. The present results are also compared with those from our previous studies of PVPh/poly(ethyl methacrylate) and PVPh/poly(vinyl ethyl ether) blends.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry