Synthesis and anionic polymerization of silacyclopropane derivatives, 2-n-butyl-l-sec-butyl-1-tert-butylsilacyclopropane (1s1t2n-BuSP) and 2-n-butyl-1-tert-butyl-1-isobutylsilacyclopropane (1i1t2n-BuSP), were investigated. These monomers were prepared by treatment of sec-butyl-tert-butyldichloro-silane or tert-butylisobutyldichlorosilane with lithium in the presence of I-hexene. Monomers 1s1t2n-BuSP and 1i1t2n-BuSP could be polymerized with a butyllithium initiator in THF at -78 degreesC in the presence of hexamethylphosphoramide (HMPA). After precipitation in methanol, poly(2-n-butyl-1-sec-butyl-1-tert-butylsilacyclopropane) (poly(1s1t2n-BuSP)) (M-n = 2100, M-w/M-n = 1.53, relative to a polystyrene standard) and poly(2-n-butyl-1-tert-butyl-1-isobutylsilacyclopropane) (poly(1i1t2n-BuSP)) (M-n = 1800, M-w/M-n = 1.60) were obtained. Contact angles of water with poly(1s1t2n-BuSP) and poly(lilt2n-BuSP) were determined as 103 and 102degrees, respectively. This significantly high hydrophobicity is probably due to the unusually large number of methyl groups in the repeating unit.