Copolymerization of propylene and disubstituted diallylsilanes involving intramolecular cyclization with stereoselective zirconocene catalysts

The copolymerization of propylene and disubstituted diallylsilanes [(CH₂ =CH-CH₂-)₂R₂Si (R = CH ₃ 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 ¹³C 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.