Molecular Mass and Dynamics in PMA-d₃ in the Glass Transition Region
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The segmental dynamics through the glass transition region, by which the glassy polymer becomes rubbery, are not well understood. Free volume, thermodynamic and kinetic theories have been used to describe the phenomenon behind the glass transition and some of those theories were tested with computer simulations. Different experimental techniques, such as NMR, thermo-mechanical analysis (TMA), differential scanning calorimetry (DSC), dilatometry and dynamic mechanical analysis (DMA) have all been also used to probe this important phenomena. Deuterium (2H) NMR has been a valuable tool for the investigation of the dynamics of macromolecules. Deuteration of macromolecules at specific locations on the chains does not significantly affect the properties of polymers. Spiess et al. Investigated motions in the glass transition region using 1D and 2D exchange NMR experiments on deuterated polystyrene. Rössler et al. studied the molecular dynamics in deuterated binary liquids close to the glass transition temperature (Tg) using 2D Exchange NMR. Blum et al. studied the effect of molecular mass on dynamics through glass transition for poly(methyl acrylate) (PMA). They found a “homogeneity” of the dynamics in the glass transition region for high molecular mass sample, but heterogeneity for the low molecular mass sample. In addition, the polydispersities of the samples were large. In this paper, we report studies of the dynamics of more monodisperse poly(methyl acrylate)-d3 (PMA)-d3 samples around the glass transition region using 2H quadrupole echo NMR and modulated DSC (MDSC).