Fusible elastomers from mixtures of polysiloxanes containing methyl, vinyl and hydrogen groups with boron modified siloxanes and peroxides

An elastomer-forming composition comprises, by weight, (1) 100 parts of a diorganopolysiloxane having an average molecular weight not less than 2 x 105, (2) 0 to 20 parts of a linear siloxane having not less than 0.5 Si-bonded H atoms per Si atom and a molecular weight not greater than 20,000, (3) 5 to 60 parts of a boron-modified siloxane, (4) 15 to 100 parts of a reinforcing or semi-reinforcing filler and (5) 0.5 to 10 parts of a curing agent. Siloxanes (1) and (2) may contain alkyl, alkenyl, aryl, fluoroalkyl, fluoroaryl, cyanoalkyl, cyanoaryl, aminoalkyl or aminoaryl radicals. Siloxane (3) is a siloxane modified by heating it with a boron compound either along or together with FeCl3 or other compound, the boron compounds specified being a boric acid or an anhydride thereof, an alkali or alkaline earth metal derivative or metal complex of a boric acid, a boron hydride or a complex thereof with ammonia or hexamethylenetetramine, a boron oxide, a hydrocarbon borate, a boron halide or a boronic or diboronic acid. Fillers specified are silicas (fume, precipitated and aerogel). Curing agents specified are benzoyl, 2 : 4-dichlorobenzoyl, dicumyl, t-butylcumyl and di-t-butyl peroxides, t-butyl peracetate, 2 : 5-dimethyl - 2 : 5 - di - (t-butyl peroxy) hexane and 2 : 5-dimethyl-2 : 5-di-(tbutyl peroxy) hexyne-3. Examples are given, in which Fe2O3 is used as an additive. Uses: The compositions may be sheeted or extruded; and may be applied to glass cloth (see Division B2).ALSO:An elastomer-forming composition comprising, by weight, (1) 100 parts of a diorganopolysiloxane, (2) 0-20 parts of a linear siloxane containing Si-bonded H atoms, (3) 5-60 parts of a boron-modified siloxane, (4) 15-100 parts of a silica filler, and 0,5-10 parts of a curing agent (see Division C3), may be applied to a substrate, e.g. glass cloth, by calendering, dipping or knife coating, followed by curing. The cured coating can be made to adhere to itself by pressure alone; further, since an improved bond develops if the cured composition is elongated, it is useful to use a substrate cut on the bias. The examples illustrate the coating of glass cloth tapes by dipping in a solvent dispersion of the composition.