Composition for promoting adhesion of curable silicones to substrates

DETAILED DESCRIPTION OF THE INVENTION The new and improved adhesion promoters of the subject invention are the diorganocyclopolysiloxanes, generally represented by the formula: ##STR16## wherein R.
sup.
1 may be C.
sub.
1 -C.
sub.
6 alkyl, C.
sub.
1 -C.
sub.
6 gamma-trihaloalkyl or phenyl; R.
sup.
2 is alkylene of from 2 to 6 carbon atoms; R.
sup.
3, R.
sup.
4, and R.
sup.
5 are, independently, C.
sub.
1 -C.
sub.
6 alkyl or C.
sub.
2 -C.
sub.
6 alkanoyl; and n is either 3 or 4.
Especially preferred adhesion promoters within the above formula are: 1,3,5-trimethyl-1,3,5-trimethoxysilylethylcyclotrisiloxane, e.
g.
, ##STR17## and 1,3,5,7-tetramethyl-1,3,5,7-tetrakis-trimethoxysilylethylcyclotetrasiloxan e, e.
g.
, ##STR18## The diorganocyclopolysiloxane adhesion promoter compounds of the subject invention may be prepared by first dissolving a methylhydrogencyclo- tri- or tetrasiloxane in an aromatic organic solvent, such as toluene, to form approximately a 20% solution.
The solution is heated to reflux and a minor catalytic amount, for example three drops, of a platinum complex catalyst is added.
Suitable platinum complex catalysts are those prepared and described in U.
S.
Pat.
No.
3,220,972 to Lamoreaux and in U.
S.
Pat.
No.
3,775,452 to Karstedt respectively.
Each of the above-identified patents are assigned to the same assignee as the present invention and each patent is specifically incorporated herein by reference.
Thereafter a stoichiometric amount of the corresponding vinyl or vinylalkyltrialkoxy or triacyloxysilane is added and the ensuing exothermic addition reaction is allowed to proceed with the rate of addition of silane being controlled by the rate of reflux.
The solution is then refluxed for a period of about two hours after all of the silane has been added.
The aromatic solvent is then stripped from the solution by, for example, heating under a vacuum, and the diorganocyclotri- or tetrasiloxane adhesion promoter compound is obtained.
The diorganocyclopolysiloxanes prepared in accordance with the subject invention are particularly useful for promoting the adhesion of curable silicone compositions to a variety of substrates