Effect of Network Chain Length Distribution and In situ Precipitated Silica on the Low-Temperature Behaviour of Poly(dimethylsiloxane) Model Networks

摘要

Polydimethylsiloxane (PDMS) model networks have been prepared with unimodal and bimodal distributions of molecular weights between crosslinks Mc. Portions of each of the elastomers were filled with silica (SiO2) using the novel technique of in situ precipitation. The low temperature properties (103-298 K) of the unfilled and filled PDMS networks in the unstretched state were investigated using differential scanning calorimetry. The glass transition temperatures of the materials showed little dependence on the molecular weight between crosslinks, unimodality or bimodality or presence of filler in marked contrast with the behaviour reported for other commercial elastomers. A single crystalline melting peak was observed for each of the PDMS model networks suggesting that the junction points inhibit the melting-recrystallization of the original crystallities, and that this process is a likely source of the double endothermic peaks commonly observed for linear PDMS. Keywords: Model networks; Differential scanning calorimetry; Glass transition; Polymer crystallization; Silica; Elastomeric materials; Siloxane; Reprints. (mjm)