Secondary relaxations in poly(allyl alcohol), PAA, and poly(vinyl alcohol), PVA. II. Dielectric relaxations compared with dielectric behaviour of amorphous dried and hydrated cellulose and dextran

This work deals with the characterisation of the dielectric secondary relax ations of poly(allyl alcohol) (PAA) and poly(vinyl alcohol) (PVA) and its c omparison with the cellulose and dextran dielectric behaviour. Cellulose an d dextran are two polysaccharides made of glucosyl repeat units. Cellulose has two hydroxyl groups (OH) and one hydroxymethyl group (CH2OH) per glucos e ring, while dextran has three OH groups and no CH2OH group. PAA and PVA a re the two simplest vinyl polymers containing CH2OH and OH lateral groups, respectively. They exhibit only one broad dielectric secondary relaxation w ith characteristics in between those of the gamma and beta mechanical relax ations in drie d PAA. Each of these apparently unique relaxations is succes sfully explained and modelled by the overlaps of two relaxation processes, gamma ' and beta '. The gamma ' relaxation, related to the rotation of side groups (CH2OH for PAA and OH for PVA), has characteristics close to those of the gamma mechanical relaxation for dried PAA. The beta ' relaxation cor responds to more or less cooperative motions of main-chain segments. Furthe rmore, the influence of moisture on the secondary dielectric relaxations of PAA and PVA is discussed on the basis of a competition between gamma ' and beta ', where the intensity of beta ' (gamma ') increases (decreases) with increasing water content. (C) 2001 Published by Elsevier Science Ltd.