Thermodynamic and Kinetic Considerations in the Copolymerization of Ethylene and Carbon Dioxide

The thermodynamics of ethylene and carbon dioxide copolymerization are assessed with average bond dissociation energies, the Benson additivity method, and density functional theory (DFT) calculations (B3LYP 6-31G†). The DFT results suggest that formation of the alternating copolymer is exothermic (ΔH = −4.31 kcal/mol per repeat unit), but endergonic at most temperatures (>−159 °C, the ceiling temperature), and therefore it is practically inaccessible because of entropic factors. However, these thermodynamic calculations show that the polymerization is favorable (exergonic) at room temperature (25 °C) when the molar quotient of ethylene/carbon dioxide exceeds 2.37 (29.7 mol % CO2 or less). Various copolymerization conditions with catalytic amounts of late transition metal complexes (Fe, Co, Ni, Cu) in combination with MAO (methylaluminoxane) produced oligomers or polymers containing only ethylene. The lack of ester functionality, as confirmed by mass spectrometry and 13C NMR, attests to the dubious nature of previous reports claiming up to 30 mol % incorporation of carbon dioxide.