Segmental Dynamics of Bulk Poly(vinyl Acetate)-d₃ by Solid-state ²H NMR: Effect of Small Molecule Plasticizer


The effect of dipropyleneglycol dibenzoate, a plasticizer, on the glass-transition temperature (Tg) of poly(vinyl acetate) was studied using deuterium solid-state NMR and modulated differential scanning calorimetry (MDSC) from 0 to 20% plasticizer content. Quadrupole-echo 2H NMR spectra were obtained for methyl deuterated PVAc-d3 samples with different plasticized amounts. The Tgʼs of different plasticized samples were determined from NMR as the temperatures at which the deuterium powder patterns collapsed. It was found that the Tgʼs decreased by approximately 6 °C for every 5% increment in the plasticizer content and that the trends in the NMR-determined Tgʼs, that is, Tg(NMR), were consistent with those determined by modulated differential scanning calorimetry (MDSC). The Tg(NMR) values were about 36 °C above those of the Tg(DSC) values. This difference in the Tgʼs was due to the different time scales of the two experiments which could be accounted for on the basis of time−temperature superposition principles. The experimental NMR line shapes were fitted using a set of simulated spectra generated from the MXQET simulation program. The spectra were based on a model of nearest-neighbor jumps on a truncated icosahedron (soccer ball). The resulting average correlation times were also found to fit a time−temperature superposition with the same parameter. While the Tg was decreased by the amount of plasticizer, it was found that the breadth of the transitions from either the NMR line shapes or the MDSC thermograms did not seem to change much with the amount of added plasticizer.




National Science Foundation (U.S.)

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