Copolymerization of ω‐Alkenyltrimethylsilane/Propylene with Heterogeneous Ziegler‐Natta Catalyst: How Dose Alkenyl Length Affect Comonomer Incorporation?

Abstract Three ω ‐alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3‐butenyltrimethylsilane, 5‐hexenyltrimethylsilane, and 7‐octenyltrimethylsilane, are copolymerized with propylene over a heterogeneous Ziegler‐Natta catalyst. The experimental results reveal that, at odds with what the molecular volumes will foretell, 5‐hexenyltrimethylsilane top the three ω ‐alkenyltrimethylsilanes in incorporation rate into PP while 3‐butenyltrimethylsilane becomes the most sluggish of the three. This comonomer incorporation rate order is in line with that of ω ‐alkenylmethyldichlorosilanes in copolymerization with propylene‐synthesizing long‐chain‐branched PP (LCB‐PP), pointing to a peculiar alkenyl length effect on comonomer incorporation rate for these comonomers. DFT simulation is then applied to seek energetic basis in coordination‐insertion for such an effect. It is revealed that complexation abilities of the three ω ‐alkenyltrimethylsilanes decrease in the following order: 3‐butenyltrimethylsilane > 5‐hexenyltrimethylsilane > 7‐octenyltrimethylsilane, in line with their molecular sizes. However, the insertion energy barriers increase in the order of: 5‐hexenyltrimethylsilane < 7‐octenyltrimethylsilane < 3‐butenyltrimethylsilane. The repulsive interaction between the bulky trimethylsilane functionality of ω ‐alkenyltrimethylsilanes and growing PP chain is found to contribute significantly to the insertion energy barrier, which grows disproportionally large with 3‐butenyltrimethylsilane. The current discovery will be conducive to understanding the more complex ω ‐alkenylmethyldichlorosilane/propylene copolymerization that synthesizes the industrially important LCB‐PP.