Fluorosilicone rubber composition, process and polymer

Claim 1

In a solvent resistant room temperature vulcanizable silicone rubber composition comprising (A) a mixture composed of (i) a vinyl-terminated base polymer, said base polymer being prepared by copolymerization of methyl-3,3,3-trifluoropropylsiloxane cyclic trimer and octamethylcyclotetrasiloxane, and the viscosity of said base polymer varies from 1,000 to 200,000 centipoise at 25° C., and (ii) a platinum catalyst, and (B) alone, or in admixture with base polymer (i), (iii) a cross-linking polymer selected from (a) a resin having ##STR10## and SiO 2 units where the R to Si ratio varies from 1.0 to 2.7; (b) a resin having ##STR11## units, SiO 2 units and RR 3 SiO units where the R to Si ratio varies from 1.2 to 2.7; (c) a polymer of the formula: ##STR12## where R is alkyl of from 1 to 8 carbon atoms or phenyl, R 1 is perfluoroalkyl of from 1 to 8 carbon atoms, s is at least 1, t and z may be zero or a positive integer and the viscosity or the polymer varies from 10 to 1,000 centipoise at 25° C., where the concentration of siloxy units taken t times varies from 0 to 75 mole percent, and R 3 is alkyl of 1 to 8 carbon atoms, or --CH 2 CH 2 R 1 ; or a mixture of (a), (b) and (c), the total composition (A) and (B) comprising per 100 parts by weight of a base polymer (i), from 0.1 to 50 parts per million of platinum catalyst (ii), and from 1 to 50 parts of cross-linking polymer (iii), the improvement wherein the cyclic trimer used in the preparation of said base polymer (i) contains no more than 1.0 weight percent of a difluoropropenyl-containing compound of the formula ##STR13##