Hardenable, addn.-crosslinking mixt. of Si cpds. for electrical insulation, contains liq. components (a) 100 pts. wt. linear organopolysiloxane mixt., (A), (b) 0.4-5 pts. wt. organoalkoxysilane (B), (c) 0.15-2 pts. wt. organosilicon-bonded methacrylic acid gp. and (d) 0.01-0.1 pts. wt. soluble Pt cpd. contg. 2-10% Pt, to activate the addn. reaction between Si-H and CH2=CH-Si. The organopolysiloxanes of (A) have different average degree of polymerisation "n1-3" consisting of 5-20 pts. wt. n1 = 50-100, 70-90 pts. wt. n2 = 270-330 and 5-25 pts. wt. n3 = 750-850. The polymers contain 2 vinyl gps. bonded to 2 Si atoms/mol. Further Si atoms are bonded with monovalent hydrocarbyl and/or halogenated hydrocarbyl gps. and 0.1% OH gps. are bonded to the linear chains. (B) are esp. organo-di- or tri-alkoxysilanes having formula (CH2=CMe-COOR)4-n-Si-Xn (where R is -CH2-, -C2H4-, -C3H6-; X is -OMe, -OEt, -OCH2CH2OMe or -OCH2-OEt; and n = 2, 3). The mixt. is used as a coating-, casting- and/or sealing compsn., esp. for insulating casting bodies and for low-, medium- and high voltage appts. for indoor and outdoor use. The crosslinked elastomers adhere well to solid substrates. Pot time at room temp. can be prolonged. The end prods. have excellent dielectric properties. The mixts. are inert to amines.
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