Method for preparing storage stable, one part curable polyorganosiloxane compositions
AssigneeDow Corning Corporation
InventorsGloria Janik, Manuel Buentello, III
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Abstract
The substantial and upredictable increases in viscosity and cure time observed during storage of curable organosiloxane compositions obtained by blending large quantities of the ingredients disclosed in U.S. Pat. No. 4,584,631 are reduced by blending to homogeniety a mixture comprising at least one member from the classes of organohydrogensiloxanes, platinum catalysts and platinum catalyst inhibitors disclosed in this patent and allowing the resultant mixture to age from 14 days to about 4 months before being combined with a vinyl-containing polymer to form one of said curable compositions.
Claims6
In a method for preparing a one-part, heat curable organosiloxane composition, said method comprising blending to homogeniety
- (A) at least one organosiloxane copolymer consisting essentially of from 80 to 96.5 mol percent of (CH.sub.3).sub.2 SiO units, from 2.0 to 10.0 mol percent of CH.sub.3 SiO.sub.1.5 units, from 1.25 to 6.0 mol percent of (CH.sub.3).sub.3 SiO.sub.0.5 units and from 0.25 to 4.0 mol percent of (CH.sub.3).sub.2 (CH.sub.2 .dbd.CH)SiO.sub.0.5 units;
- (B) an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule, no more than one silicon-bonded hydrogen per silicon atom and organic radicals selected from the group consisting of alkyl containing from 1 to 6 carbon atoms per radical, phenyl and 3,3,3-trifluoropropyl, said organohydrogensiloxane providing from 0.7 to 1.2 silicon-bonded hydrogen atoms per silicon-bonded vinyl radical present in said composition;
- (C) a platinum catalyst in an amount sufficient to promote the reaction of (A) and (B), and
- (D) a platinum catalyst inhibitor of the formula R.sup.1.sub.2 NR.sup.3 NR.sup.2.sub.2 or R.sup.4 NH.sub.2 in an amount sufficient to impart long term storage stability at temperatures of up to 70.degree. C., where each R.sup.1 is individually selected from alkyl radicals containing from 1 to 4 carbon atoms, R.sup.2 is R.sup.1 or hydrogen, R.sup.3 represents an alkylene radical containing from 2 to 4 carbon atoms, and R.sup.4 represents an alkyl radical containing from 2 to 4 carbon atoms, the improvement consisting essentially of the following sequence of steps:
- (1) forming a homogeneous mixture of said organohydrogensiloxane, said platinum catalyst and said platinum catalyst inhibitor,
- (2) aging said mixture for a period of at least 14 days under ambient conditions, and
- (3) combining the aged mixture with said organosiloxane copolymer to form said curable composition.
Dependencies are inferred from the claim text.