RHEOLOGICAL IMAGES OF POLY(VINYL CHLORIDE) GELS - 6 - EFFECT OF TEMPERATURE

Dynamic viscoelastic properties of poly(vinyl chloride) (PVC)/bis(2-et hylhexyl) phthalate (DOP) gels with different molecular weights and va rious polymer concentrations have been studied as a function of temper ature. These PVC gels exhibited an elastic solid at room temperature a nd gradually became liquid (sol) with increasing temperature. The sol- gel transition took place ata critical gel temperature at which the sc aling law of G'(omega) similar to G ''(omega) proportional to omega(n) held, allowing an accurate determination of the critical gel temperat ure by means of the frequency independence of the loss tangent. The sc aling exponent n obtained was 0.75, independent of temperature as well as molecular weight. This is in good agreement with the previous resu lts observed at 40 degrees C and suggests the formation of a similar f ractal structure of the PVC gels. Furthermore, the molecular structure of the gel junctions was analyzed using the modified Eldridge-Ferry p rocedure developed by Tanaka and Nishinari. The junction structure was found to be almost independent of molecular weight and gelation tempe rature, giving a support to the similarity of the fractal structure in the PVC gels.