Role of the stereosequences of poly(vinyl alcohol) in the rheological properties of syndiotacticity-rich poly(vinyl alcohol)/water solutions

Syndiotacticity-rich poly(vinyl alcohols) (sPVAs) with various syndiotactic dyad (S-dyad) contents were prepared by the copolymerization of vinyl pivalate and vinyl acetate with various monomer feed ratios, which was followed by the saponification of copoly(vinyl pivalate/vinyl acetate) to investigate the effect of the stereosequences of s-PVA on the rheological properties of s-PVA/water solutions. Through a series of experiments, we identified that the syndiotacticity had a profound influence on the rheological properties of s-PVA/water solutions. Over a frequency range of 10^-1 to 10² rad/s, s-PVAs with higher S-dyad contents showed larger values of complex viscosity and storage modulus and more shear thinning at similar molecular weights and degrees of saponification of the polymer, suggesting that poly(vinyl alcohol) molecules were stiffer and more readily oriented as syndiotacticity increased. All the yield stresses of s-PVA represented positive values, and s-PVAs with higher syndiotacticity showed higher yield stresses. This suggests that as syndiotacticity increased, more pseudostructures were present in s-PVA/water solutions.