Patent ID: 7601792

Claim:
A method of preparing a silicone resin comprising adding 50 parts to less than 100 parts by weight of water at pH 1 to 7 to 100 parts by weight of a mixture of components (A), (B) and (C) for effecting cohydrolytic condensation to form a silicone resin and an alcohol by-product, and distilling off the alcohol until the liquid temperature reaches 95° C., said mixture consisting of (A) a tetraalkoxysilane having the general formula: Si(OR′) 4 wherein R′ is an alkyl group of 1 to 3 carbon atoms, or a partial hydrolytic condensate thereof, (B) a trialkoxysilane having the general formula: R 1 Si(OR′) 3 wherein R 1 is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group and R′ is as defined above, or a partial hydrolytic condensate thereof, and (C) a dialkoxysilane having the general formula: (R 2 ) 2 Si(OR′) 2 wherein R 2 is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group and R′ is as defined above, or a partial hydrolytic condensate thereof, wherein the total of components (A), (B) and (C) is 100 Si mol %, the content of component (A) is 1 to 50 Si mol % based on the total of components (A), (B) and (C), the content of component (B) is 50 to 99 Si mol % based on the total of components (A), (B) and (C), and the content of component (C) is 0 to 10 Si mol % based on the total of components (A), (B) (C), thereby obtaining a silicone resin having a number average molecular weight of 2,390 to 40,000 as measured by gel permeation chromatography (GPC), and containing units of the formula: R 1 SiO (3-p)/2 (OX) p derived from component (B) wherein X is hydrogen or R′, R 1 and R′ are as defined above, and p is an integer of 0 to 3, in which units of the formula: R 1 SiO 3/2 wherein R 1 is as defined above account for 30 to 80 mol % and the total of units of the formulae: R 1 SiO 2/2 (OX) and R 1 SiO 1/2 (OX) 2 wherein R 1 and X are as defined above accounts for 20 to 70 mol %, as analyzed by silicon nuclear magnetic resonance spectroscopy ( 29 Si-NMR).