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 ata critical gel temperature at which the scaling law of G'(omega) similar to G "(omega) proportional to omega(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 degrees 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.