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.