Silalactones and methods for their preparation and use

A method comprising heating, under substantially anhydrous conditions, a reaction mixture comprising a halide salt catalyst selected from the group consisting of quaternary ammonium halide salts, quaternary phosphonium halide salts and alkyl pyridinium halide salts and an ester having the formula X.sub.2 RSiQCOOR' wherein X denotes a chlorine or bromine atom, R denotes a monovalent hydrocarbon radical, Q denotes a divalent hydrocarbon radical, there being at least two carbon atoms in Q separating a silicon atom and a carbonyl carbon atom, and R' denotes an alkyl radical, said heating being sufficient to produce a silalactone composition having the formula ##STR35## wherein X, R and Q have the meanings recited above and n has an average value greater than zero and further comprising mixing water with the silalactone composition in sufficient amount to hydrolyze substantially all hydrolyzable bonds attached to silicon in the silalactone composition and to provide an organopolysiloxane containing one or more siloxane units having the formula ##STR36## wherein R and Q have the stated meanings.