Investigation of the properties of fully reacted unstoichiometric polydimethylsiloxane networks and their extracted network fractions

We investigated the linear dynamic response of a series of fully reacted unstoichiometric polydimethylsiloxane networks and of the two corresponding network fractions namely the sol and the washed network. The sol and the washed network were separated by a simple extraction process. This way, it was possible to obtain rheological data from the washed network without interference from the sol fraction and furthermore from the sol fraction without interference from the elastic washed network. When the stoichiometry increased towards perfectly reacted networks and beyond, we observed harder networks both qualitatively and by rheology, and the properties of the two fractions became more and more different. At the gel point, the sol fraction and the washed networks have more or less identical properties which our data also show. The storage and loss moduli, G' and GaEuro(3), were analysed with the gel equation as proposed by Winter and Chambon (J Rheol 30:367-382, 1986) and Chambon and Winther (J Rheol 31:683-697, 1987). We observed that one of the investigated samples which before the swelling experiment did not show any elastic response gave an elastic washed network after swelling; this was verified by analysis with the gel equation. We also calculated the weight fraction of the sol fraction by using the theory by Villar et al. (Macromolecules 29(11):4072-4080, 1996) and compared this with experimentally found values.