Segmental and secondary dynamics in hydrogen-bonded poly(4-vinylphenol)/ poly(methyl methacrylate) blends

Broadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen-bonded poly(4-vinylphenol)/ poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20-80% and at temperatures from -30 to approximately glass-transition temperature (T _g) + 80°C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry T _g and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher T _g. This leads to well-defined α and β relaxations in the blends above the corresponding T _g, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above T _g, but with an activation energy larger than that observed below T _g because of increased relaxation amplitude.