A series of polymers of the type [Si(CH3)(C(3)H(6)R)CH2](n) where R = C3H7, NEt(2), carbazole, and OC2H4OC2H4OCH3 were prepared by hydrosilation of the appropriate terminal olefin with the [Si(H)(CH3)CH2](n), (1) polymer using Karsted’s catalyst. It was found that hydrosilation of these olefins with 1 proceeds with a relatively high (80-95%) conversion of the polymer SIH groups. NMR and DSC data on these polymers as well as their relative thermal and oxidative stabilities are reported. The phenol-substituted polymers, [Si(CH3)(C3H6C6H4OH)X](n) (5), where X = O (5e) or CH2 (5f), were also prepared and their stability toward base hydrolysis was evaluated. It was found that the polycarbosilane 5f shows superior hydrolytic stability relative to the polysiloxane 5e.