Restoring thermorheological simplicity in miscible polymer blends: How many hydrogen bonds are required?

The linear viscoelastic properties of blends of poly(vinyl methyl ether) (PVME) with poly(styrene) (PS), poly(styrene-stat-vinylphenol) (PSVPh) copolymers, and poly(vinylphenol) (PVPh) in different proportions were measured over a wide temperature range (0-160 °C). All blends were miscible over the temperature and composition ranges covered. The amount of hydrogen bonding was tuned by using copolymers with varying mole fractions of vinylphenol units (10%, 20%, and 50%). The time-temperature superposition principle (tTS) was used to create master curves from the rheological data. For some PS/PVME and PSVPh/PVME blends there was a clear failure of tTS. In contrast, tTS was successful for all the PVPh/PVME blends and PSVPh/PVME blends with higher vinylphenol content, despite much higher differences between the component T_gs. These results confirm that the dynamic response of two polymers can be effectively coupled in the presence of sufficient hydrogen-bonding interactions, whereby the temperature dependences of the two-component relaxation times become equivalent. By using an established model for predicting the extent of hydrogen bonding, the concentration of hydrogen bonds necessary to couple the dynamic behavior, as reflected by the success of tTS, was estimated. The size of the associated 'control volume' is comparable to the Kuhn length.