Organopolysiloxanes containing group IV organometallic substituents in the side chains

In an attempt to increase the intermolecular attraction between polyorganosiloxane chains and rings, polar groups have been introduced into methyl groups attached to the silicon atoms. To avoid the usual weakening of the CSi bond by negative polar substituents, positive substituents of the type (CH3)3M (where M is Si, Ge, or Sn) were employed in this study. Cyclic trimers and extended linear polymers were prepared, both from the pure polar‐substituted monomers and from mixtures of these monomers with octamethyltetrasiloxane. Intermolecular attraction was estimated by measuring viscositities and activation energies of viscous flow. The preparations also were compared in these respects with pure dimethylsiloxanes and with neopentylsiloxanes. The results show that intermolecular attraction is increased by the positive polar substitutents, and that the CSi bond is rendered more stable toward OH− attack by such positive substituents than by negative. More detailed analysis indicates that the effects of the groups on the viscosity of the polymers depends on: (1) the dipole attraction of the polar groups, (2) the bulk or steric effect of the enlarged group, and (3) the effect of the metal M upon the ease of rotation of the methyl groups (the characteristically free intramolecular motion of silicon polymers). The trends of these effects oppose each other in the CSiGeSn series, and so limit the observed increase of viscosity.