| 摘要 |
Compsn. polyorganosiloxane exhibiting thermal stability when crosslinked comprises organophilic particles dispersed throughout the compsn. made from at least one metallic oxide in the form of polycrystalline particles of max. size 50 nm (made from 4 - 6 nm crystals) and a treated surface of BET between 250 and 300m<2>/g, pref. 250 mg<2>/g. Also claimed is a transparent polyorganosiloxane elastomeric material obtd. by hardening the claimed compsn. Pref. the metal oxide is chosen from alumina, silica, transition metal oxides, esp. TiO2, and rare earth oxides, esp. CeO2. The organophile particles are prepd. by reacting a hydroalcoholic suspension of polycrystalline particles with a soln. of alcoholic anhydride consisting of at least one alkoxysilane of formula Si(OR)xR'4-x (I). R = 1-6C alkyl esp. methyl or ethyl; R' = alkyl, cycloalkyl, aryl, alkylaryl, arylalkyl, alkenyl or alknyl, esp. octyle, dodectyl or octadectyl; and x = 1 to 3, esp. 3. The polycrystalline particles are prepd. by reacting metal oxide polycrystalline particles with at least one tetra-alcoxysilane of formula Si(OR'')4 (II). R" = 1-5C alkyl. The compsns. contains between 0.1 and 5% organophilic particles pref. 0.3 to 1%. The organophilic particles comprise 60 to 90% TiO2 and 40 to 10% SiO2. |
