Secondary relaxations in poly(allyl-alcohol), PAA, and poly(vinyl alcohol), PVA Part I.: Mechanical relaxations compared with mechanical behavior of cellulose and dextran in the presence of polar solvent

As a team project, a molecular simulation study of thermally activated localized motions in polysaccharides, such as cellulose and dextran is required to determine the molecular origin of their secondary relaxations and the influence of polar solvents on these relaxations. Nevertheless, the complexity of polysaccharides led to the idea of testing the simplest polymer that could present similar mechanical behavior. Poly(allyl alcohol), PAA, and poly(vinyl alcohol), PVA, are the two simplest polymer containing hydroxymethyl and hydroxyl lateral groups, respectively, PVA is a commercial polymer, but PAA was synthesized by the reduction of poly(methyl acrylate) and characterized by infrared (IR) and C-13 Nuclear Magnetic Resonance (NMR) spectroscopy. PVA and PAA, with different water or methanol contents, were characterized by dynamic mechanical analysis (DMA). The dried PAA presents two secondary relaxations, the so called gamma(PAA) and beta(PAA) whereas PVA presents only one secondary relaxation, beta(PVA) For both polymers, characteristics and influence of polar solvent content on the beta secondary relaxation are very close to the results obtained previously for cellulose and dextran. Such a comparison has been done to sort out the molecular origin of the gamma secondary mechanical relaxation in polymers presenting polar side groups (vinyl polymers and polysaccharides). It appears that hydroxymethyl moieties are involved in this relaxation. (C) 2000 Elsevier Science Ltd. All rights reserved.