Nanostructure and crystallisation kinetics of poly(ethylene oxide)/poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) blends

Blends of poly(ethylene oxide) (PEO) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM) were studied by means of synchrotron small and wide angle X-ray scattering (SAXS and WAXS, respectively) and by differential scanning calorimetry (DSC). The DSC measurements were used in the determination of the Flory–Huggins interaction parameter and also to study the isothermal and non-isothermal crystallisation kinetics of the PEO/PVPh-HEM blend. The interaction parameter, χ₁₂, was found to be negative (between −0.5 and −2.5, approximately) and presented a significant dependence on the blend composition, which is expected for a system with specific interactions such as hydrogen bonding. From the kinetic studies with Kissinger, Friedman and Avrami models, it was shown that crystallisation of PEO chains is slower in the blend than in the pure polymer, despite the decrease in the energy barrier to the crystallisation with the increase in PVPh-HEM concentration.

From the SAXS and WAXS profiles, the nanostructure of the blend was elucidated, exhibiting the formation of PEO lamellae even in the blends containing high concentrations of PVPh-HEM, which are non-crystalline (as observed by the WAXS profiles). The thickness of the PEO lamellae (R_c, approximately 8 nm) remains almost unchanged with the blend composition, while the crystalline peaks, observed at 19.78 and 23.98°, vanish, and the WAXS profile exhibits only a non-crystalline halo. For the non-crystalline blends with high concentrations of PVPh-HEM, PEO chains keep their crystalline structural memory.