| 主权项 |
1. A process for preparing a resin-linear organosiloxane block copolymer comprising:
I) reacting
a) a linear organosiloxane having the formula
R1q(E)(3-q)SiO(R12SiO2/2)nSi(E)(3-q)R1q,wherein each R1, at each occurrence, is independently a C1 to C30 hydrocarbyl,n is 10 to 400, q is 0, 1, or 2,E is a hydrolyzable group containing at least one carbon atom, andb) an organosiloxane resin comprising at least 60 mole % of [R2SiO3/2] siloxy units in its formula, wherein each R2 is independently a C1 to C20 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 mole % of disiloxy units [R12SiO2/2] and 10 to 60 mol % of trisiloxy units [R2SiO3/2], andwherein 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 weight average molecular weight (Mw) of the resin-linear organosiloxane block copolymer by at least 50%, wherein the crosslinking reaction is promoted by a superbase, III) optionally, further processing the resin-linear organosiloxane block copolymer; and IV) optionally, removing the organic solvent. |
