Investigation on LCST behavior of a new amorphous/crystalline polymer blend: Poly(n-methyl methacrylimide)/poly(vinylidene fluoride)

The liquid-liquid phase-separation (LLPS) behavior of poly(n-methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small-angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (Tc) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min⁻¹ and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, Tc of PMMI/PVDF is higher than its melting temperature (Tm) and a large temperature gap between Tc and Tm exists. At the early phase-separation stage, the apparent diffusion coefficient (Dapp) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn-Hilliard-Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism.