Patent ID: 8921493

Claim:
A process for preparing a resin-linear organosiloxane block copolymer comprising: I) reacting a) a linear organosiloxane having the formula R 1 q (E) (3-q) SiO(R 1 2 SiO 2/2 ) n Si(E) (3-q) R 1 q , where each R 1 is independently a C 1 to C 30 hydrocarbyl, n is 10 to 400, q is 0, 1, or 2, E is a hydrolyzable group containing at least one carbon atom, and b) an organosiloxane resin comprising at least 60 mol % of [R 2 SiO 3/2 ] siloxy units in its formula, where each R 2 is independently a C 1 to C 20 hydrocarbyl, in c) an organic solvent to form a resin-linear organosiloxane block copolymer; wherein the amounts of a) and b) used in step I are selected to provide the resin-linear organosiloxane block copolymer with 40 to 90 mol % of disiloxy units [R 1 2 SiO 2/2 ] and 10 to 60 mol % of trisiloxy units [R 2 SiO 3/2 ], and wherein at least 95 weight percent of the linear organosiloxane added in step I is incorporated into the resin-linear organosiloxane block copolymer, II) reacting the resin-linear organosiloxane block copolymer from step I) to crosslink the trisiloxy units of the resin-linear organosiloxane block copolymer sufficiently to increase the average molecular weight (M w ) of the resin-linear organosiloxane block copolymer by at least 50%, III) optionally, further processing the resin-linear organosiloxane block copolymer to enhance storage stability and/or optical clarity, IV) optionally, removing the organic solvent.