Dynamic exponent of PDMS networks at the sol-gel transition

Five model polydimethylsiloxanc (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH containing crosslinker. Viscoelastic experiments were performed in order to study the influence of molecular parameters on the dynamic properties at the sol-gel threshold. The results suggest that the critical exponents are not universal and depend on the chemical structure of the incipient gels. They show that the fractal dimension calculated from the theological data in the framework of the viscoelastic mean field theory, is a decreasing function of the ratio functionality/molecular weight of the crosslinker. (C) 2003 Elsevier Ltd. All rights reserved.