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

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 c g, 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 c g ∝ M w -1 . The scaling exponent n obtained was constant ( n = 0.75) and independent of the molecular weight of PVC. The gel strength S g at the gel point decreased with increasing PVC molecular weight. A constant gel strength ( S g / c g = 1.27 × 10 -2 Pa s 0.75 g -1 L) was obtained by normalizing the gel strength S g with c g to eliminate the effects of M w . These results suggest a unique character and structure at the gel point of the gelling system.