초록 ▼

The tear strength of cured organosiloxane elastomers can be increased and the compression set value reduced without adversely affecting other physical properties if the composition used to prepare the elastomer is curable by a platinum-catalyzed hydrosilation reaction and contains a mixture of two l

The tear strength of cured organosiloxane elastomers can be increased and the compression set value reduced without adversely affecting other physical properties if the composition used to prepare the elastomer is curable by a platinum-catalyzed hydrosilation reaction and contains a mixture of two liquid diorganoalkenylsiloxy terminated polydiorganosiloxanes, one of which constitutes from 96 to 99.5 percent by weight of said mixture and contains the alkenyl radicals only at the terminal positions. The second polydiorganosiloxane contains both terminal alkenyl radicals and from 1 to 5 mole percent of alkenyl radicals on non-terminal repeating units.

대표청구항 ▼

In a curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 96 to 99.5 weight percent, based on the total weight of (A) and (B), of a first diorganoalkenylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of from 5 to 20 Pa.s at 25 degrees C.

In a curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 96 to 99.5 weight percent, based on the total weight of (A) and (B), of a first diorganoalkenylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of from 5 to 20 Pa.s at 25 degrees C. and containing essentially no alkenyl radicals bonded to non-terminal silicon atoms; B. a second diorganoalkenylsiloxy terminated polydiorganosiloxane that is miscible with said first polydiorganosiloxane and exhibits a viscosity of from 0.1 to 20 Pa.s at 25 degrees C., where from 1 to 5 percent of the non-terminal repeating units of said second diorganoalkenylsiloxy-terminated polydiorganosiloxane contain an alkenyl radical; C. an amount sufficient to cure said composition of an organohydrogensiloxane that is miscible with (A) and (B), and contains an average of more than two silicon bonded hydrogen atoms per molecule, D. a hydrosilation catalyst comprising a metal from the platinum group of the periodic table or a compound of said metal, the amount of said catalyst being sufficient to promote curing of said composition at a temperature of from ambient to 250 degrees C., and E. from 10 to 60 weight percent, based on the weight of said composition, of a reinforcing silica filler that is treated with at least one organosilicon compound, where the organic radicals bonded to the silicon atoms of (A), (B) and (C) are monovalent hydrocarbon or halogenated hydrocarbon radicals, the improvement comprising the presence in said composition of from 0.5 to 4 weight percent, based on the combined weights of (A) and (B), of said second diorganoalkenylsiloxy terminated polydiorganosiloxane, whereby the tear strength of cured elastomers prepared from said composition is from 35-45 kilonewtons per meter and the compression set values of said elastomers is less than 35%.