Abstract: A platinum catalyst composition having improved thermal stability, and all of the utilities of platinum catalyst compositions of the art, is provided by mixing certain organosiloxanes which contain aryl and alkenyl groups, such as 1,3-divinyl-1,3-diphenyldimethyldisiloxane, in a quantity of at least 2 moles, with a platinum complex having as a ligand an organosiloxane which contains alkyl and alkenyl groups, such as 1,3-divinyltetramethyldisiloxane (or a mixture of said platinum complex and said organosiloxane), in a quantity of 1 mole of platinum atoms. In a preferred embodiment the mixture is distilled in vacuo to remove part or all of the organosiloxane which contains alkyl and alkenyl groups, and most preferably to remove at least a portion of the complexed organosiloxane which contains alkyl and alkenyl groups.

Abstract: A platinum catalyst composition having improved thermal stability, and all of the utilities of platinum catalyst compositions of trhe art, is provided by mixing certain organosiloxanes which contain aryl and alkenyl groups, such as 1,3-divinyl-1,3-diphenyldimethyldisiloxane, in a quantity of at least 2 moles, with a platinum complex having as a ligand an organosiloxane which contains alkyl and alkenyl groups, such as 1,3-divinyltetramethyldisiloxane (or a mixture of said platinum complex and said organosiloxane), in a quantity of 1 mole of platinum atoms. In a preferred embodiment the mixture is distilled in vacuo to remove part or all of the organosiloxane which contains alkyl and alkenyl groups, and most preferably to remove at least a portion of the complexed organosiloxane which contains alkyl and alkenyl groups.