Rheological Images of Poly(vinyl chloride) Gels. 1. The Dependence of Sol−Gel Transition on Concentation

Abstract

Dynamic viscoelastic properties of poly(vinyl chloride) (PVC)/bis(2-ethylhexyl) phthalate (DOP) solutions and gels have been studied as a function of polymer concentration and molecular weight. All PVCs were linear polymers and had a similar distribution in molecular weight. Increasing the polymer concentration gradually from the liquid state to the solid state allowed the rheological observation of the sol−gel transition. The gel point cg, which depends on the polymer concentration, was accurately determined by the frequency independence of loss tangent in the vicinity of the sol−gel transition and was found to be inversely proportional to the molecular weight as expressed by cg ∝ Mw-1. The scaling exponent n obtained was constant (n = 0.75) and independent of the molecular weight of PVC. The gel strength Sg at the gel point decreased with increasing PVC molecular weight. A constant gel strength (Sg/cg = 1.27 × 10-2 Pa s0.75 g-1 L) was obtained by normalizing the gel strength Sg with cg to eliminate the effects of Mw. These results suggest a unique character and structure at the gel point of the gelling system.