Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.