| abstract |
(a = 0 or 1), while the remaining siloxane units, apart from the triorganosiloxane units, contain at least 99 mole percent from units of the formula exist with an average viscosity of 50 to 2000 mPa.s at 25 ° C andn n n (C) contain photosensitizer, wherein Si-bonded hydroxyl groups, which are in units of formula are, at most in amounts of 0, 2 hydroxyl groups per grouping of the formula are availablen n n and in these compositions a total of at most 0.02 percent by weight, based on the total weight of the components (A), (B) and (C), organic titanium or organic tin compounds are crosslinkable by ultraviolet light and are excellent for embedding electronic components. Masses as essential componentsn n n (A) Organopolysiloxane with units of the formula HR 1 C = CR 2 COOR 3 SiR 2 R 2 O 1 , 2 where R is a monovalent, optionally halogenated hydrocarbon radical, R 1 is hydrogen or an optionally halogenated phenyl radical, R 2 is hydrogen or an alkyl radical with 1 up to 4 carbon atoms per radical and R 3 is a divalent hydrocarbon radical which can be halogenated, 2 such siloxane units per molecule being present, while the remaining siloxane units contain at least 80% of their number of those of the formula with an average viscosity of 20 to 5000 mPa.s at 25 "Cn n n (B) by units of the formula n n n n End-blocked organopolysiloxane with 0.05 to 5 mole percent units of the formula |