Hexamethylcyclotrisiloxane was found to undergo photoinitiated cationi
c ring-opening polymerization in solution and bulk, upon exposure to U
V radiation, in the presence of either sulfonium or iodonium salts or
an iminosulfonate derivative. Glass transition temperatures were below
-100 degrees C. Molecular weights, determined by size exclusion chrom
atography relative to polystyrene standards, increased with photolysis
lamp intensity. Use of an iodonium photoinitiator afforded poly(dimet
hylsiloxane) with Mn = 172,000. Polymerization of hexamethylcyclotrisi
loxane was accompanied by a small increase in volume (3-4%).