Copolymerization of ω-Alkenyltrimethylsilane with Ethylene by MgCl2/TiCl4 Catalyst: Effect of Alkenyl Length on Comonomer Incorporation

ω-Alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3-butenyltrimethylsilane, 5-hexenyltrimethylsilane, and 7-octenyltrimethylsilane, are used as model compounds to study the alkenyl length effect in copolymerization of ethylene with steric-hindered tri-substituted silane-functionalized α-olefins over MgCl₂/TiCl₄ catalysts. The experimental results reveal that 3-butenyltrimethylsilane tops the three α-olefins in incorporation rate into PE while 7-octenyltrimethylsilane is slightly better than 5-hexenyltrimethylsilane. The coordination-insertion events for different ω-alkenyltrimethylsilanes are investigated by DFT simulation. The results suggest that the three ω-alkenyltrimethylsilanes encounter similar energy barriers during insertion, with similar repulsive interactions between the bulky trimethylsilane substituent and growing PE chain found in the energy decomposition of transition state configuration. However, complexation abilities at the Ti active site for the three ω-alkenyltrimethylsilanes follow the order of 3-butenyltrimethylsilane > 5-hexenyltrimethylsilane > 7-octenyltrimethylsilane, in line with their molecular compactness, which are deemed to be where the alkenyl length effect originates in the ω-alkenyltrimethylsilane/ethylene copolymerization.