Perfectly alternating copolymerization of CO2 and epichlorohydrin using cobalt(III)-based catalyst systems

Area of Science:

• Polymer Chemistry
• Green Chemistry
• Catalysis

Background:

• Carbon dioxide utilization via copolymerization with epoxides yields biodegradable polycarbonates.
• Previous research primarily used aliphatic epoxides, with limited success for epoxides bearing electron-withdrawing groups like epichlorohydrin.
• Developing efficient catalysts for CO2 copolymerization with diverse epoxides is crucial for sustainable chemical synthesis.

Purpose of the Study:

• To report the selective synthesis of CO2 copolymers using epichlorohydrin and CO2.
• To investigate the kinetic differences between cyclic carbonate and polycarbonate formation for epichlorohydrin and propylene oxide.
• To elucidate the mechanism of CO2/epichlorohydrin copolymerization using advanced analytical techniques.

Main Methods:

• Alternating copolymerization of CO2 and epichlorohydrin using binary and bifunctional (salen)cobalt(III) catalysts.
• In situ infrared spectroscopy for comparative kinetic studies of cyclic carbonate vs. copolymer formation.
• Electrospray ionization mass spectrometry (ESI-MS) for direct observation of polymer chain species.

Main Results:

• Production of CO2 copolymers with over 99% carbonate linkages from epichlorohydrin.
• Kinetic analysis revealed a smaller activation energy difference for copolymerization with epichlorohydrin (45.4 kJ/mol) compared to propylene oxide (53.5 kJ/mol), indicating greater difficulty in selective copolymer synthesis.
• ESI-MS confirmed the perfectly alternating structure of the resulting copolymer and suggested potential intermediates involving MTBD.

Conclusions:

• The study successfully produced high-purity polycarbonates from CO2 and epichlorohydrin, showcasing a significant advancement in CO2 utilization.
• Kinetic insights explain the challenges in selective copolymerization with electron-deficient epoxides.
• The findings provide a mechanistic basis for developing more efficient catalysts for CO2-based polymer synthesis.