Reactivity of Difunctional Polar Monomers and Ethylene Copolymerization: A Comprehensive Account

A comprehensive picture of insertion of 1,1-disubstituted difunctional olefins, their ability to double the functional group density at the same level of incorporation as that of monofunctional olefin, and copolymerization with ethylene has been demonstrated. Exposure of a palladium complex [{P∧O}­PdMe­(L)] (P∧O = κ2-P,O–Ar2PC6H4SO2O with Ar = 2-MeOC6H4; L = C2H6OS) to methyl 2-acetamidoacrylate (MAAA) revealed slight preference for 1,2-insertion over 2,1-insertion (1.0:0.7). In contrast, insertion of electron-deficient 2-(trifluoro­methyl)­acrylic acid (TFMAA) unveiled selective 2,1-insertion {via [(P∧O)­PdC5H6F3O2] (11)}. The unstable intermediate 11 undergoes β-hydride and β-fluoride elimination to produce subsequent insertion and elimination products. The identity of elimination products (E/Z)-2-trifluoromethyl)­but-2-enoic acid [17(E/Z)] and 2-(difluoro­methylene)­butanoic acid (13) was fully established by 1–2D NMR spectroscopy. These insertion experiments, taken together with insertion rates, suggest that MAAA and TFMAA are amenable to insertion. Polymerization of ethylene with MAAA, TFMAA, acetamidoacrylic acid, 2-bromoacrylic acid, dimethyl allylmalonate, and allylmalonic acid was catalyzed by [{P∧O}­PdMe­(L)] (L = C2H3N) (5.ACN), and the highest incorporation of 11.8% was observed for dimethyl allylmalonate (DMAM). The changes in the surface properties of the copolymers after incorporation of difunctional olefins were evaluated by measuring the water contact angle. Copolymer with highest (11.8% of DMAM) incorporation revealed a reduced water contact angle of 76°. These findings demonstrate that 1,1-disubstituted difunctional olefins are amenable to polymerization, and incorporation of difunctional olefins in polyethylene backbone leads to the production of relatively hydrophilic polyethylene copolymers.