Viscometric Investigation of Dimethylsiloxane Polymers

Abstract

The intrinsic viscosities of an extended series of linear methyl polysiloxane fluids, having dimethylsiloxane (Me2SiO) as the repeating unit, have been determined in toluene solution. These values have been correlated with their molecular weights, determined chemically and by osmotic pressure and light scattering measurements. The Staudinger equation was found applicable only for fluids of relatively low molecular weights, i.e., up to about 2500; for the higher polymers, the best correlation of intrinsic viscosity with number average molecular weight was found to be: [η]=2×10−4Mn0.66. This held reasonably well for molecular weights from 2500 to about 200,000. The bulk viscosities of the polysiloxane fluids were found to conform to the Flory relationship for melt viscosities; the expression: log visc. (cs. at 25∘C)=1.00+0.0123 Mn12appears to be reasonably valid for molecular weights above 2500.