Rheological Images of Poly(vinyl chloride) Gels. 6. Effect of Temperature

Dynamic viscoelastic properties of poly(vinyl chloride) (PVC)/bis(2-ethylhexyl) phthalate (DOP) gels with different molecular weights and various polymer concentrations have been studied as a function of temperature. These PVC gels exhibited an elastic solid at room temperature and gradually became liquid (sol) with increasing temperature. The sol−gel transition took place at a critical gel temperature at which the scaling law of G‘(ω) ∼ G‘‘(ω) ∝ ω n held, allowing an accurate determination of the critical gel temperature by means of the frequency independence of the loss tangent. The scaling exponent n obtained was 0.75, independent of temperature as well as molecular weight. This is in good agreement with the previous results observed at 40 °C and suggests the formation of a similar fractal structure of the PVC gels. Furthermore, the molecular structure of the gel junctions was analyzed using the modified Eldridge−Ferry procedure developed by Tanaka and Nishinari. The junction structure was found to be almost independent of molecular weight and gelation temperature, giving a support to the similarity of the fractal structure in the PVC gels.