STUDIES ON DIELECTRIC BEHAVIOR OF DIMETHYLDIALKOXYSILANES

Fourteen numbers of dimetbyldialkoxysilanes were prepared by reacting dimethylchlorosilane and corresponding alcohols in the liquid phase. P roperties like density, viscosity, molecular weight, refractive index, thermal expansion coefficient, oxidation stability, flash point and p our point were determined by standard methods. Dielectric constant, di electric loss and breakdown voltage of dimethyldialkoxysilanes are det ermined and the values are compared against molecular weight, viscosit y, temperature, pour point along with the values of tetraalkoxysilanes , polydimethylsiloxanes and coolanols of Monsanto Chemicals in order t o study their dielectric behaviour. Dipole moment of the samples are o btained from the plot of molar polarization and reciprocal absolute te mperature. Dielectric constant of dimethyldialkoxysilanes increases wi th the increase in molecular size due to increase in polarizability an d decreases with rise in temperature and frequency due to reduction in the alignment of the permanent dipoles by the electric field as obser ved for the polar compounds like polydimethylsiloxanes and coolanols. The values of dielectric constant of dimethyldialkoxysilanes are highe r than those of tetraalkoxysilanes and polydimenthylsiloxanes of compa rable molecular weight due to molecular dissymmetry. Comparable dielec tric behaviour of dimethyldialkoxysilanes coupled with their better ox idative and thermal characteristics suggest that these compounds could be used in some of the power transfer and dielectric coolant applicat ions in the place of conventional materials for better performance.