PURPOSE: To obtain a fluorinated polydiorganosiloxane base wherein the tensile strength and the tear strength are improved when cured to yield an elastomer.
CONSTITUTION: The following processes from A to F are employed. (A) In a dry N2, 100 pts.wt. trifluoropropylmethylsiloxane, which has a Williams plasticity of larger than 225 and is blocked with an OH group at the terminal, is dried. (B) In a dry air stream, from 0.1 to 1.5 pts.wt. methylvinyl(N- alkylacetamide)silane of the chain-extension side is added. (C) From 5 to 20 pts.wt. methyl(trifluoropropyl)polysiloxane, wherein the terminal is blocked with an OH group, is mixed. (D) From 0 to 4 pts.wt. polydiorganosiloxane fluid wherein from about 5 to about 15 wt.% comprises vinyl groups and the remaining portion comprises methyl groups, is mixed. (E) From 25 to 50 pts.wt. fumed silica having a surface area of 200 m2/g or larger is uniformly mixed and dispersed. (F) While mixing, the mixture is heated under a reduced pressure of at least 150 mmHg at 130°C or higher for 1 hour or longer.
RANDARU ARAN SHIIGERU
ROTSUKO JIYOSEFU BOSHI
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