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

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.