AQUEOUS SOLUBILITY OF PERMETHYLSILOXANES (SILICONES)

The aqueous solubility of several low molecular weight linear, cyclic, and branched permethylsiloxanes was determined at room temperature. A method for preparing molecularly dispersed, colloid-free saturated aq ueous solutions is described. Solubilities, decreasing with increased molecular weights, ranged downward from one part per million to mere p arts per trillion. The cyclic oligomers were slightly more soluble tha n their linear analogues. While the effect of branching was mixed, pol ar groups such as phenyl and hydroxyl moities sharply increased aqueou s solubility. Semilog plots of the solubility/molecular weight yielded linear regressions, the extrapolation of which indicate the absence o f any environmentally relevant water solubility (< 1 ppt) for the conv entional higher molecular weight polydimethylsiloxanes of commerce.