Coupling of Component Segmental Relaxations in a Polymer Blend Containing Intermolecular Hydrogen Bonds

Abstract

The segmental relaxations of poly(4-vinylphenol)/poly(vinyl ethyl ether) [PVPh/PVEE] blends, with PVPh content from 10 to 50 wt % and having a very large Tg difference between the components, have been investigated using broadband dielectric spectroscopy. Although a single Tg was observed for all compositions in DSC measurements, two segmental α processes for blends with low PVPh concentration are highly probable. The slow process is attributed to the relaxation of intermolecular hydrogen-bonded PVPh and PVEE segments, while the fast one is assigned to unassociated PVEE segments. However, at PVPh concentrations ≥30 wt %, most PVEE segments are hydrogen-bonded to PVPh and the blends exhibit a single α relaxation. This behavior is compared to that of other miscible blends with large Tg contrast but having weak intermolecular interactions. The observed behavior is explained by the role of intermolecular hydrogen bonding, which is believed to be capable of coupling the segmental relaxations of PVEE and PVPh, which would otherwise exhibit two distinct segmental relaxation processes due to their large intrinsic mobility difference. The time−temperature superposition principle, which fails for many polymer blends, is successful in blends with higher PVPh content, indicating thermorheological simplicity of this dynamically asymmetric blend. Finally, increases in both the fragility and the coupling parameter are clearly observed in the blends compared to neat PVEE, confirming that intermolecular coupling is enhanced by hydrogen bonding.