Abnormal segmental dynamics of poly(methyl methacrylate)/poly(vinylidene fluoride) blends by mechanical spectroscopy

The molecular relaxation dynamics of PMMA/PVDF blends above the glass transition temperature (Tg) over a wide composition range are studied by mechanical spectroscopy combined with differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. The mechanical spectra of the blends reveal the existence of two relaxation modes: α, ascribed to the glass transition, and α′, related to the softening dispersion composed of the sub-Rouse modes and the Rouse modes. At ϕPVDF = 40%, both the α and α′ relaxation processes shift to low-temperatures and are accelerated, which is due to the formation of the interphase and unfavourable interchain entanglements in the intermediate composition. The abnormal dynamics of the blend at ϕPVDF = 40% is further confirmed by the observed weak interaction between PMMA and PVDF from FTIR measurements and an obvious drop of the intermolecular coupling from the Coupling Model. However, the longer α′ relaxation shows a different dynamic behavior from the α relaxation for the blends with increasing the PVDF content at ϕPVDF ≤ 40%, which is due to the structure evolution and the change of chains entanglement with heating. This work enriches the understanding of the complex relaxation dynamics and the structure evolution in PMMA/PVDF blends.