Room temperature vulcanizable siloxane block copolymer

Claim 1

The room temperature vulcanizable composition of claim 1 wherein Y is acetoxy.

Claim 12

A method for preparing a room temperature vulcanizable composition comprising (I) mixing in an inert organic solvent under anhydrous conditions (A'') a hydroxyl terminated polydiorganosiloxane which is a mixture of (1'') a hydroxyl terminated polydiorganosiloxane having an average from 6 to 40 inclusive diorganosiloxane units per molecule and (2'') a hydroxyl terminated polydiorganosiloxane having an average from 200 to 500 inclusive diorganosiloxane units per molecule, said hydroxyl terminated polydiorganosiloxanes (l'') and (2'') being present in the mixture in amounts sufficient to provide an average of 25 to 460 diorganosiloxane units per molecule in the mixture, said hydroxyl terminated polydiorganosiloxane block (A'') being at least 80 mol percent dimethylsiloxane units based on the total number of siloxane units in (A'') and any remaining units being selected from the group consisting of phenylmethylsiloxane units and monomethylsiloxane units and said hydroxyl terminated polydiorganosiloxane (A'') having from 0.1 to 1.82 weight percent silicon-bonded hydroxyl radicals, and (B'') a trifunctional organosilane of the formula RSiX3 in which R is a monovalent organic radical selected from the group consisting of phenyl, vinyl, methyl, ethyl and propyl radicals and X is a hydrolyzable radical elected from the group consisting of acetoxy, ketoxime, chlorine and alkoxy wherein (B'') is present in an amount sufficient to provide at least one RSiX3 per silicon-bonded hydroxyl radical whereby a RS2SiO0.5 terminated polydiorganosiloxane is obtained in an inert organic solvent, (II) adding under anhydrous conditions to the RX2SiO0.5 terminated polydiorganosiloxane in an inert organic solvent obtained in (I), (C'') a hydroxylated organosiloxane resin of the average unit formula R''xSiO4 x/2 where r'' is a monovalent organic radical selected from the group consisting of an aryl radical, a methyl radical, a ethyl radical and a propyl radical and x has an average value of from 1 to 1.3 inclusive in said hydroxylated organosiloxaNe resin at least 50 percent of the monovalent organic radical being aryl radicals and from 2 to 10 weight percent silicon-bonded hydroxyl radicals based on the total weight of (C''), the mixture is agitated at a temperature of from room temperature to 130* C. for at least 15 minutes whereby a hydroxylated organosiloxane block copolymer having from 0.5 to 5 weight percent silicon-bonded hydroxyl radicals is obtained in an inert organic solvent, thereafter (III) adding under anhydrous conditions to the hydroxylated organosiloxane block copolymer obtained in (II), (D'') a trifunctional organosilane of the formula R''''SiY3 in which R'''' a monovalent organic radical selected from the group consisting of an alkyl radical having from 1 to 5 inclusive carbon atoms a phenyl radical and a vinyl radical and Y is a hydrolyzable radical selected from the group consisting of acetoxy, alkoxy radicals having from 1 to 5 inclusive carbon atoms per radical and ketoxime radicals of the formula -O-N Z wherein Z is selected from the group consisting of radicals of the formula R''''''2C and in which each Riv is selected from the group consisting of divalent hydrocarbon radicals and halogenated divalent hydrocarbon radicals and each R'''''' is a radical selected independently from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, and (IV) maintaining to the mixture of (III) at a temperature of from room temperature to 200* C. for a time sufficient to essentially render the hydroxylated organosiloxane block copolymer free of silicon-bonded hydroxyl radicals whereby a R''''SiY2O0.05 endblocked organosiloxane block copolymer is obtained, (A'') being present in an amount sufficient to provide from 24 to 84 inclusive mol percent diorganosiloxane units (B'')+(C'') being present in an amount sufficient to provide from 11 to 68 inclusive mol percent organosiloxane units, and (D'') being present in an amount sufficient to provide from 2 to 27 inclusive mol percent R''''SiY2O0.5 endblock units, the sum of (A''), (B''), (C'') and (D'') being 100 mol percent.