Abstract
It is well known that poly(vinyl alcohol) (PVA) in the mixed solvent of dimethysulphoxide (DMSO) and water converts to a thermoreversible gel with a phase transition near room temperature. In this study, syndiotactic-rich PVA samples with high-molecular weight (degree of polymerization N between 4600 and 23600) were synthesized. The thermal stability of PVA gels was evaluated from their gel-melting temperature, and the Young’s modulus E was determined by tensile test and compression test. From there, junction size was estimated as a function of N. The junction length ζ in number of vinyl alcohol units and multiplicity S in number of PVA chains were estimated from the Tanaka-Stockmayer theory (TS theory). Gel-melting temperatures of syndiotactic-PVA gels were higher than those of atactic-PVA gels. The PVA junction point was found to be crystalline and its length ζ increased slowly with increasing N for N < 104, above which it showed a plateau region. Both Young’s modulus E and junction size ζ × S increased with increasing degree of polymerization N and number of syndiotactic-diads.
