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 $N∕N_e$, where $N$ and $N_e$ are, respectively, the numbers of Kuhn monomers between branch points and between entanglements. For $N∕N_e<1$, the growth mechanism of clusters is the critical percolation and $u=0.69$, and for $N∕N_e>1$, the growth mechanim of clusters is the diffusion-limited cluster aggregation and $u=0.76$.

• Received 14 September 2006

DOI:https://doi.org/10.1103/PhysRevE.75.011802