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 relaxations of poly(allyl alcohol) (PAA) and poly(vinyl alcohol) (PVA) and its comparison with the cellulose and dextran dielectric behaviour. Cellulose and dextran are two polysaccharides made of glucosyl repeat units. Cellulose has two hydroxyl groups (OH) and one hydroxymethyl group (CH2OH) per glucose ring, while dextran has three OH groups and no CH2OH group. PAA and PVA are the two simplest vinyl polymers containing CH2OH and OH lateral groups, respectively. They exhibit only one broad dielectric secondary relaxation with characteristics in between those of the γ and β mechanical relaxations in dried PAA. Each of these apparently unique relaxations is successfully explained and modelled by the overlaps of two relaxation processes, γ′ and β′. The γ′ relaxation, related to the rotation of side groups (CH2OH for PAA and OH for PVA), has characteristics close to those of the γ mechanical relaxation for dried PAA. The β′ relaxation corresponds to more or less cooperative motions of main-chain segments. Furthermore, the influence of moisture on the secondary dielectric relaxations of PAA and PVA is discussed on the basis of a competition between γ′ and β′, where the intensity of β′ (γ′) increases (decreases) with increasing water content.