Microwave Absorption and Molecular Structure in Liquids. LXX. Dipole Moment, Atomic Polarization, and Dielectric Relaxation in Polymethylpolysiloxanes

Abstract

Dielectric constants and losses have been measured at wavelengths of 0.22, 1.25, 3.22, 10.01, and 57 500 cm at temperatures of 25°, 40°, and 60° for four liquid polymethylpolysiloxanes of the general formula (CH3)3Si[OSi(CH3)2]xOSi(CH3)3, where x=1, 2, 3, and 5. The data have been used to calculate the small dipole moments, very large atomic polarizations, and two rather small dielectric relaxation times for the molecules. The squares of the dipole moments, the atomic polarizations, and the relaxation times are found to be linear functions of the size of the molecule as measured by x, the number of (CH3)2SiO groups. It is concluded that dipole orientation or relaxation occurs by molecular rotation and by intramolecular motion, which includes group rotation around Si–O bonds and, probably, bending of the Si–O–Si bonds. The bending and twisting of these bonds are the principal causes of the large atomic polarizations, as the absorption frequencies associated with them extend into the far infrared.