Synthesis and post-functionalization of poly(3-acyloxycyclopentene)s with controllable regioregularity and narrow dispersity

Abstract

ROMP of 3-acyloxycyclopentenes (3ROCOCPEs) with low ring strain energies was investigated by changing the steric bulkiness of the allylic substituent. The polymers having narrow dispersity (Đ < 1.5) and high/controlled regioregularity (88–93% head-to-tail) were obtained by using sterically bulky 3ROCOCPE monomers with trifluoromethanesulfonamide-based ruthenium catalyst at low temperatures. The equilibrium reaction was effectively driven towards polymerization, and chain transfer was suppressed at low temperatures, as evidenced by low dispersity. Regioselectivity, caused by the distal and proximal approach modes of the ruthenium catalyst to the monomer, was also controlled. The distal approach is generally preferred due to steric repulsion of catalysts and substituents in the case of proximal approach, resulting in higher head-to-tail insertions. Reaction energies in the possible regioregular pathways were investigated using Density functional theory (DFT) calculation, proving that the distal face addition is thermodynamically favored due to the steric hindrance between the ruthenium catalyst and the allylic substituents in the case of proximal face addition. The resulting regioregular poly(3MeOCOCPE) was further investigated through post-functionalization via allylic azidation, which exhibited a controllable degree of N3 functionalization (2–74% efficiency). Finally, N, O-mixed polymer with controlled amine functionality was obtained through subsequent reduction. The amine-functionalized polymer is a value-added polymer that could be expected to interact with various molecules due to its high polarity, basicity and nucleophilicity.