Abstract
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.
Highlights
Compared to the development of new polymeric structures or monomers, polymer blends provide attractive interest in polymer science due to the enhancement of properties of a pure polymer by mixing it with one or more other polymers
The absorbance peaks at 1680 cm-1 and 1726 cm-1 attributed to carbonyl groups of pure poly(methyl methacrylate) (PMMA),36 and its intensity changes in PMMA/Poly(vinylidene fluoride) (PVDF) blends
This is due to the formation of hydrogen bonding between the carbonyl groups of PMMA and CH2 groups of PVDF, which hinder the vibration of carbonyl groups and reduce its intensity
Summary
Compared to the development of new polymeric structures or monomers, polymer blends provide attractive interest in polymer science due to the enhancement of properties of a pure polymer by mixing it with one or more other polymers. The dynamics of the blends with a large composition range was studied by Lu et al., and they found that the dynamic heterogeneity in segmental relaxations for the blends is determined by the presence of the crystal-amorphous interphase, which is responsible for the reduced viscosity and speedup relaxation in the blends These studies have certainly advanced our understanding of the dynamic heterogeneity and thermorheological complexity of the blends, the structural evolution and dynamics of PMMA/PVDF blends are still not being well understood yet, especially for the dynamics of interphase and the longer-scale dynamics such as sub-Rouse modes and Rouse modes. The different relaxation dynamics of the α and α modes of PMMA/PVDF blends depending on the composition were compared to reveal the structure evolution and the change of chains entanglement during heating process. The samples were all protected in argon atmosphere with a pressure of 0.1 MPa to avoid degradation and oxidation
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