Patent ID: 7750077

Claim:
A method of preparing a polyorganosiloxane resin having at least two different types of siloxy units, R 3 SiO 1/2 units (M units) and SiO 4/2 units (Q, and optionally Q OH , units, where said Q OH units are Q units having SiOH units on the surface), wherein R is independently selected from C 1 -C 18 alkyl groups and C 2 -C 20 alkenyl groups; said method comprising the following steps: (a) preparing a polyorganosiloxane resin comprising Q units from an alkali metal silicate in acid medium in a reaction vessel; (b) functionalizing the siloxane resin obtained in step (a) with (1) halosilanes in the presence of an apolar solvent, wherein by-products comprising volatile oligosiloxanes (silox by-products) are formed during the functionalizing process; and (2) silox by-products recovered in step (c); (c) recovering the silox by-products that are produced in step (b); and (d) subjecting the resin functionalized in step (b) to reaction with a strong base in order to remove the silanes, wherein at least a portion of the silox by-products produced during step (b) and recovered in step (c) are recycled into step (b), and wherein the viscosity of the resin formed by said process is more consistent across reaction temperatures in step (a) than the viscosity of a resin formed by the same process without recycling at least a portion of the silox by-products produced during step (b) and recovered in step (c) into step (b).