Synthesis of an ethylene-(2-vinylpyridine) alternating copolymer the 1,4-selective polymerization of 1-(2-pyridyl)-1,3-butadiene and subsequent hydrogenation

Abstract

Alternating copolymers with unique structures have properties that are distinct from those of homopolymers and other types of copolymers, making them important in polymer science. The alternating copolymer of ethylene (E) and 2-vinylpyridine (2VP) is expected to have unique properties. However, its synthesis is highly challenging and remains unreported because of the mismatches between E and 2VP in both their coordination polymerization mechanisms and polymerization activities. Herein, we report the first synthesis of an E–2VP alternating copolymer. This is realized by the hydrogenation of poly(1-(2-pyridyl)-1,3-butadiene) with high trans-1,4-selectivity (>99%), which is achieved for the first time under the catalysis of a thiophene-fused cyclopentadienyl scandium complex (cat-Sc). Density functional theory (DFT) calculations reveal the polymerization mechanism of 1-(2-pyridyl)-1,3-butadiene (1-PyBD) catalyzed by cat-Sc, further elucidating that in the trans-1,4-re pathway, the strong η4–π interaction between the growing chain and the central metal makes this polymerization pathway the only thermodynamically feasible one, thereby governing the regioselectivity and stereoselectivity of 1-PyBD polymerization.