Polycarbosilanes were synthesized by hydrosilylation reaction of A(2) monomer containing bis Si-H moieties and B-n (n = 2 3 and 4) monomers containing di tri and tetra vinyl groups in the presence of Karstedt s catalyst The corresponding linear polycarbosilanes (LPC) and hyperbranched poly carbosilanes (HBPC) having M-n 2200-51 500 were obtained in 34-94% yield without any gel product The values of refractive index (n(D)) of the synthesized LPC and HBPC were in the range from 1 460 to 1 711 and were consistent with the structures of the synthesized products In the case of HBPC the values of nD increased with increase of number average molecular weight (K) molecular weight distribution (M-w/M-n) and glass transition temperature (T-g) apparently because of increased density due to the presence of microgels that is high refractive index hyperbranched carbosilanes could be synthesized by A(2) + B-n (n = 3 and 4) method (c) 2010 Wiley Periodicals Inc J Polym Sci Part A Polym Chem 48 5746-5751 2010