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)/wat er was investigated through rheological response. Below a critical temperat ure, 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 los s tangent (tan delta) of the solution below the critical temperature increa sed with increasing frequency. Consequently, the dilute solution of UHMW s- PVA/DMSO/water showed the rheological behaviors as can be observed in gener al chemical or physical gel systems below the critical temperature. These r esults suggest that solidlike heterogeneity prevailed in the solution befor e macroscopic gelation with decreasing temperature. Such heterogeneity was considered as phase-separated domains attributed to spinodal decomposition. (C) 2001 John Wiley & Sons, Inc.