MOLECULAR-WEIGHT DEPENDENCE OF VISCOELASTICITY OF POLYCAPROLACTONE CRITICAL GELS

The molecular weight dependence of critical gel properties was determined for poly(epsilon-caprolactone) diol end-linked with a three-functional isocyanate. The critical gels exhibit the typical scaling behavior with a power law relaxation spectrum H(lambda) = G0/GAMMA(n)(t/lambda-0)-n, lambda > lambda-0, where G0 = G(e) was found to be the modulus of the fully cross-linked polymer and lambda-0 = eta-0/G(e) was found to depend on the viscosity of the difunctional prepolymer, eta-0. The relaxation exponent, n, decreases with increasing cross-linker concentration (increasing stoichiometric ratio, r = [NCO]/[OH]) and increasing molecular weight of the prepolymer. This suggests that the fractal dimension of the critical gel increases with increasing molecular weight and stoichiometric ratio.