Rheological properties of high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (PVA)/HMW atactic PVA blend solutions

To identify the effect of blend ratios of syndiotacticity-rich poly(vinyl alcohol) (s-PVA)/atactic PVA (aPVA) having similar number-average degrees of polymerization (P-n)s of 4000 and degrees of saponification (DS)s of 99.9% on the rheological properties of s-PVA/a-PVA/water solutions, water-soluble s-PVA and a-PVA with different syndiotactic diad contents of 58.5 and 54.0%, respectively, were prepared by bulk copolymerization of vinyl pivalate and vinyl acetate (VAc) and solution polymerization of VAc, followed by saponifying the corresponding copoly(vinyl pivalate/vinyl acetate) and poly(vinyl acetate). The blend ratios played a significant role in rheological behavior. Over the frequency range of 10(-1)-10(2) rad/s, s-PVA/a-PVA blend solutions with larger s-PVA content show more shear thinning at similar (P-n)s and (DS)s of polymer, suggesting that PVA molecules are more readily oriented as s-PVA content increases. Yield stress is higher for s-PVA/a-PVA blend solutions with larger s-PVA content at similar (Pjs and (DS)s of polymer. This indicates that more domains with internal order are produced at larger s-PVA content in s-PVA/a-PVA blend solutions. (c) 2006 Wiley Periodicals, Inc.