Abstract
Seven model polydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH-containing cross-linker. Viscoelastic experiments, completed by size exclusion chromatography and static light scattering experiments, were performed in order to study the influence of molecular parameters on the dynamic properties around the sol-gel threshold. The dynamic critical parameter u was determined from experiments close to and above the sol-gel threshold. Our results show that the growth mechanism of PDMS clusters and the viscoelastic behavior are a function of the ratio N/Ne, where N and Ne are, respectively, the numbers of Kuhn monomers between branch points and between entanglements. For N/Ne<1, the growth mechanism of clusters is the critical percolation and u=0.69, and for N/Ne>1, the growth mechanim of clusters is the diffusion-limited cluster aggregation and u=0.76.