Process for the preparation of silarylenesiloxane-diorganosiloxane copolymers

Linear-chain copolysiloxanes comprising units of the general formulae (1) and (2), [-(R 1 R 2 SiO) a -] (1), [-(R 3 R 4 Si-R 7 -SiR 5 R 6 O) b -R 3 R 4 Si-R 7 -SiR 5 R 6 -] (2), the end-groups of which may be Si-H or Si-OH, are prepared by reacting: (A) diorganopolysiloxanes of the general formula (3) HO-(R 1 R 2 SiO) a -H (3) with (B) silarylenesiloxane compounds of the general formula (4) H-[(R 3 R 4 Si-R 7 -SiR 5 R 6 O) b -R 3 R 4 Si-R 7 -SiR 5 R 6 ]-H (4), in the presence of (C) a transition metal catalyst, wherein R 1 , and R 2 are optionally substituted and optionally heteroatom-containing hydrocarbon radicals, R 3 , R 4 , R 5 , and R 6 are optionally halogen-substituted and optionally heteroatom-containing aliphatically or aromatically unsaturated C 1-20 hydrocarbon radicals, and R 7 is an aromatic, optionally substituted, and optionally heteroatom-containing divalent hydrocarbon radical. The copolysiloxanes are well defined, and have internal blocks corresponding to the (3) and (4) starting materials, substantially free of rearrangement and equilibration products.