The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S-PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide-angle X-ray diffraction and compared with those of atactic poly(vinyl alcohol) (A-PVA) fibers with r = 54%. The beta(c) dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A-PVA around 120-140 degreesC, and the only primary (alpha(c)) dispersion was observed for S-PVA around 180 degreesC. The thermal expansion coefficients for the a and c axes of the A-PVA crystal changed discontinuously around 120 degreesC, which corresponded to the beta(c) dispersion. For S-PVA, the coefficient for the (002) plane changed discontinuously around 100 degreesC, similarly to A-PVA, but that for the (100) plane remained unchanged between 20 and 220 degreesC. These results showed that the intermolecular hydrogen bonding of S-PVA was stronger in the direction of the a axis than in the other directions, suppressing the beta(c) dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S-PVA decreased markedly around 180 degreesC, and this indicated that the alpha(c) dispersion was due to the torsional motion of the molecular chains in the crystalline regions. (C) 2004 Wiley Periodicals, Inc.