The copolymerization of propylene and disubstituted diallylsilanes [(CH2 =CH-CH2-)(2)R2Si (R = CH3 or C6H5)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5-disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2-insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by C-13 NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2-insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis-silacyclohexane units were mainly formed. (c) 2006 Wiley Periodicals, Inc.