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

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 ally] 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 [((PO)-O-boolean AND)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 ally] ester, inert 1,2-disubstituted acrylate), stereoselective (different diastereomers), and regioselective (five-membered gamma-butyrolactone and six-membered delta-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 H-1 NMR, C-13 NMR, DEPT, H-1-H-1 COSY, H-1-C-13 HSQC, and H-1-C-13 HMBC plus ATR-IR, DSC, and GPC.