Abstract
A study has been made of the rheological properties in the molten state of phosphorus containing polydimethylsiloxanes (PPDMS), obtained by heterogeneous polycondensation of a siloxane oligomer with M=2×10 4 with phosphoric acid, at various ratios of the reactants. It was found that the PPDMS polymers have a constant energy of activation for viscous flow of E η =10 kcal/mole and that the viscosity η max and critical rate of deformation · γ cr vary with M according to power laws with small but not identical exponents. Many of the properties are typical of an homologous polymer series. Comparison of the properties of the PPDMS polymers with those of polydimethylsiloxanes of similar molecular weight shows that the PPDMS polymers possess a combination of rheological properties characteristic of linear polymer of both low and high molecular weight. This is due to their low molecular weight and the presence of intermolecular coordinate bonds, i. e. on an entanglement network and a network of polar bonds. The polar bonds reduce the density of the entanglement network.
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