Combination of Ethylene, 1,3-Butadiene, and Carbon Dioxide into Ester-Functionalized Polyethylenes via Palladium-Catalyzed Coupling and Insertion Polymerization

Abstract

The combination of ethylene (E), 1,3-butadiene (BD), and carbon dioxide (CO2), three extensively utilized feedstocks, into a polymer via the copolymerization pathway is of great interest in both academia and industry. However, copolymerization for even two of them (E/BD, E/CO2, BD/CO2) is highly challenging; thus, copolymerization for three of them (E/BD/CO2) together is more elusive and remains unexplored. In this contribution, by employing a two-step strategy of palladium-catalyzed coupling and subsequent insertion polymerization, the E/BD/CO2 copolymerization via an allyl acrylate-type intermediate was achieved for the first time. The palladium-catalyzed [Pd(acac)2/PCy3] C–C coupling reaction of BD and CO2 followed by ring cleavage and esterification first generated the desired trifunctional monomer methyl-2-ethylidene-5-hydroxyhept-6-enoate acrylate (II). Subsequent palladium-catalyzed [(P^O)PdMedmso] coordination–insertion copolymerization of E and II afforded ester-functionalized polyethylenes including three components of E/BD/CO2. These resultant copolymers are chemoselective (reactive acrylate and allyl ester, inert 1,2-disubstituted acrylate), stereoselective (different diastereomers), and regioselective (five-membered γ-butyrolactone and six-membered δ-valerolactone) and thus are of highly novel microstructures with incorporation of noncyclic ester units and cyclic ester units into the main chain. They are comprehensively identified by 1H NMR, 13C NMR, DEPT, 1H–1H COSY, 1H–13C HSQC, and 1H–13C HMBC plus ATR-IR, DSC, and GPC.