Polymerization and reaction rate studies on substituted phenylmethylbis(dimethylamino)silanes

The synthesis of seven para- or meta-substituted phenylmethylbis(dimethylamino)-silane monomers has been carried out. These silanes were polymerized with 1,4-bis(hydroxydimethylsilyl)benzene in tetrahydrofuran at 30°C, and the polymerization kinetics were followed by monitoring dimethylamine evolution for 200 min. The polymers were quenched by precipitation in methanol and molecular weight data were obtained. The polymerizations followed second-order kinetics in every case as evidenced by the linear plots of 1/(a ? x) versus time. The molecular weight data generally correlated with the specific reaction rate constant k₂ to show an increasing polymer molecular weight with increasing polymerization rate, although the range of k₂ values obtained for the substituted aminosilanes was relatively small (2.50 × 10^?5–6.67 × 10^?5 l./mole-sec). The value of k₂ increased in the following order: p-OCH₃, p-F, m-CH₃, H, m-OCH₃, p-CF₃, 3,5-di(CF₃). The logarithms of the rate constants correlated with the σ constants for the substituents, with a reaction constant, ρ of 0.391. The displacement at silicon in these reactions is discussed in terms of bimolecular mechanisms in which a four-center transition state may participate.