Rheological properties of syndiotacticity-rich ultrahigh molecular weight poly(vinyl alcohol) dilute solution

Viscoelastic behavior of the dilute solution of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) (UHMW s-PVA)/dimethyl sulfoxide (DMSO)/water was investigated through rheological response. Below a critical temperature, the dynamic storage modulus (G′) of the solution became greater than the dynamic loss modulus (G″) and the viscoelastic exponent for G′ became smaller than that for G″ before macroscopic gelation, which indicates the evolution of viscoelastic solid properties at the sol state. Also, the loss tangent (tan δ) of the solution below the critical temperature increased with increasing frequency. Consequently, the dilute solution of UHMW s-PVA/DMSO/water showed the rheological behaviors as can be observed in general chemical or physical gel systems below the critical temperature. These results suggest that solid like heterogeneity prevailed in the solution before macroscopic gelation with decreasing temperature. Such heteogeneity was considered as phase-separated domains attributed to spinodal decomposition.