Patent ID: 6153689
Filing Date: 2000-11-28
Classification: C08G,C08K,C09D

Abstract:
A method for preparing a curable polymethylsilsesquioxane composition comprising:1) preparing a polymethylsilsesquioxane by (1) a process comprisingi) forming a two-phase system of water and solvent, wherein the solvent is selected from the group consisting ofa) an oxygenated organic solvent, andb) a mixture comprising the oxygenated organic solvent and a hydrocarbon solvent, with the proviso that the mixture contains no more than 50 volume % of the hydrocarbon solvent; andii) adding to the two-phase system a material selected from the group consisting ofc) a methyltrihalosilane of the formula CH.sub.3 SiX.sub.3, wherein X is a halogen atom selected from the group consisting of F, Cl, Br, and I; andd) a solution comprising the methyltrihalosilane and the solvent selected from the group consisting of a) and b), or (2) adding the solution d) to water, forming a two-phase system of water and solvent; and2) adding colloidal silica to the polymethylsilsesquioxane prepared in step 1), wherein the colloidal silica is added in an amount of 5 to 250 weight parts of colloidal silica per 100 weight parts of the polymethylsilsesquioxane, and with the proviso that the colloidal silica is organic solvent-borne colloidal silica,wherein said polymethylsilsesquioxane hasa predetermined number-average molecular weight, Mn, from 380 to 2,000, as determined by gel permeation chromatography calibrated with polystyrene standards and being represented by the general formula(CH.sub.3 SiO.sub.3/2).sub.n (CH.sub.3 Si(OH)O.sub.2/2).sub.mwherein m and n are positive numbers that provide the predetermined Mn, with the proviso that the value of m/(m+n) is less than or equal to 0.152/(Mn.times.10.sup.-3)+0.10 and greater than or equal to 0.034/(Mn.times.10.sup.-3).