Molecular modeling of the mobility of poly(allyl alcohol), PAA, and poly(vinyl alcohol), PVA

Detailed atomistic models of the dense glassy isotactic and syndiotactic poly(allyl alcohol) (PAA) and poly(vinyl alcohol) (PVA) have been simulated and characterized. Models of PVA display very good agreement with experimental characteristic ratio and solubility parameter, whereas no experimental data are available for PAA. Intra- and intermolecular hydrogen bonding interactions for each system were analyzed and compared with available solid-state NMR experiments. The generated microstructures have been used for a quasi-static simulation of localized molecular motions. These motions include the rotation of hydroxyl and hydroxymethyl pendant groups for PVA and PAA, respectively. The average energy barrier of the most probable conformational transition of hydroxymethyl groups in PAA and hydroxyl groups in PVA is estimated to be 45(±13) and 10(±3) kJ mol−1, respectively. The mobility of the pendant groups appears to be independent of tacticity. The influence of the side group rotation on the surrounding is very limited. The role of inter- and intramolecular hydrogen bonds is discussed. Mobility of the main-chain backbone is studied in the isotactic PVA model. It is found that the neighboring torsion angles are affected by conformational interconversions of a given backbone angle. This is explained in terms of cooperativity and geometry of the motions. The calculated energy barrier is found at an average value of 52 kJ mol−1. The calculated data on the different simulated mobilities are compared with the observed secondary relaxations measured by mechanical spectrometry.