INFLUENCE OF PENDANT CHAINS ON MECHANICAL-PROPERTIES OF MODEL POLY(DIMETHYLSILOXANE) NETWORKS .2. VISCOELASTIC PROPERTIES

Viscoelastic properties of model poly(dimethylsiloxane) networks with pendant chains composed of linear molecules of known and uniform molec ular weights are studied. It was found that the loss modulus (G'') of these networks depends on the concentration and the molecular weight o f the dangling chains. The dependency of the relaxation times of penda nt chains on their molecular weights, proposed by de Gennes, was verif ied using the values of G'' measured experimentally. Elastic propertie s of these networks decrease due to the presence of the pendant chains . This results in a reduction in the amount of elastically active chai ns. Low-frequency elastic moduli of the networks are coincident with e quilibrium Values predicted by the theory of rubber elasticity, provid ed that the contribution of trapped entanglements is taken into accoun t. Values of elastic moduli obtained from swelling experiments also sh ow excellent agreement with theoretical values.