Closing the Loop of Cyclopolymerization of Nonconjugated α,ω-Diolefin Diasteroselectivity and α-Olefin Polymerization Enantioselectivity

Abstract

The cyclopolymerization of α,ω-dienes catalyzed by transition metals (TMs) is one of the most attractive synthetic routes for the production of cyclic polyolefins (COPs). These COPs exhibit unique properties that confer enhanced performance and durability, making them highly desirable for advanced applications. By variation of the catalytic system, controlled microstructures of COPs can be achieved, particularly regarding the configuration of cyclic units and the cyclization ratio. The relationship between the catalyst structure, diastereoselectivity, and cyclization efficiency in the cyclopolymerization of 1,5-hexadiene (1,5-HD) and 1,7-octadiene (1,7-OD) has been explored by a combined study based on the density functional theory (DFT) calculation and experimental study involving the synthesis and characterization of the resulting polymers. DFT calculations explained the trans-selectivity of the majority of metallocene and nonmetallocene systems as well as the peculiar cis-selectivity of the nonmetallocene pyridylamido complex for 1,5-HD polymerization. The predicted diastereoselectivity was successfully corroborated by ¹H and ¹³C NMR spectroscopic data collected from the synthesized polymers. Analyses by WAXS and DSC and the study of mechanical properties were performed to investigate their structural/property relationships. DFT calculations have been used also for explaining the experimental switching to cis-selectivity for the cyclopolymerization of 1,7-OD achieved by the TM systems promoting the trans-selectivity of 1,5-HD. The comparison with the enantioselectivity of α-olefin polymerization has been used as a key guideline for this work closing the loop between the diastereoselectivity of nonconjugated α,ω-diolefin cyclopolymerization and the enantioselectivity of the α-olefin polymerization.