Influence of metallic palladium on thermal properties of polysiloxane networks

Polysiloxane networks differing in cross-link densities were prepared by hydrosilylation of linear polysiloxanes containing various amounts of vinyl groups uniformly distributed in their chains. Thus, D2V polymer with a vinyl group at every third Si atom in the macromolecule and 4D3V3 copolymer with vinyl groups located in a block constituting one fifth of its chain were reacted with hydrogensiloxanes of different molecular structures and functionalities in the presence of Karstedt catalyst. The process was conducted at excessive amounts of Si-H groups with respect to vinyl ones which ensured that unreacted Si-H groups remained in the polysiloxane networks formed. Such systems were treated with palladium(II) acetate solution in THF. As established by X-ray diffraction and FTIR spectroscopic studies, the redox reaction between Pd2+ ions from the solution and Si-H groups of the networks occurred which resulted in the appearance of metallic Pd particles in the systems. Systematic investigations conducted using thermogravimetry coupled with mass spectrometry allowed to conclude that the presence of Pd modifies thermal properties of polysiloxane networks, influencing mainly redistribution of Si bonds taking place during thermolysis of the systems. It was found that higher cross-link densities of the D2V polymer-derived networks than those of the 4D3V3 copolymer-based ones are beneficial for thermal stability of the systems with incorporated Pd. The type of the cross-linking agent, in turn, decides on residual mass remaining after pyrolysis of the Pd-containing samples conducted at 1000 °C in Ar flow.