Stress relaxation of end-linked polydimethylsiloxane elastomers with long pendent chains

Two important issues in the area of stress relaxation in elastomers are addressed experimentally in this paper. The first deals with the dependence of the terminal relaxation time on the number of entanglements that a chain tethered to a network makes with the network, and the second deals with the validity of the empirical Chasset-Thirion equation, By carefully end-linking PDMS chains to form networks with few defects besides the controlled amount of long pendent chains, our results show a much weaker exponential dependence of the terminal relaxation time on number of entanglements per tethered chain than predicted by the Doi-Kuzuu theory for a fixed entanglement network but closer to the exponential dependence predicted by lattice calculations with a harmonic potential. The Chasset-Thirion equation is found to hold only in an intermediate time regime of the relaxation spectrum.