Effects of dangling chains on some dynamic mechanical properties of model poly(dimethylsiloxane) networks

Summary

Elastomeric networks of polydimethylsiloxane (PDMS)) prepared previously for studying the effects of dangling chains on equilibrium elastomeric properties are now studied with regard to their dynamic mechanical properties. These model irregular networks had been prepared by end-linking divinyl-terminated PDMS chains having a number-average molecular weight of 11.3×10³ g mol^-1. The tetrafunctional end-linking agent present was used in varying amounts smaller than that corresponding to stoichiometric balance between its active hydrogen atoms and the chain vinyl groups. The resulting networks were studied from-135 to-28 °C using a Rheovibron DDV III Viscoelastometer. The glass transition temperature Tg was found to be generally insensitive to the concentration of dangling chains, over the range 0 to 41.1 wt %. The intensity of the tan δ relaxation, however, decreased significantly with increase in concentration over most of this range, suggesting the dangling chains facilitated crystallization. At the highest concentration, tan δ begins to increase, however, presumably because the inherent energy-dissipating ability of the dangling chains finally predominates.