Received: March 06, 2020;   Published: May 14, 2020

DOI: 10.32474/AOICS.2020.04.000190

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Abstract

The catalytic copolymerization reaction of carbon dioxide and cyclohexene oxide (CHO) using the single-site chromium (III) Schiff base catalyst, [Cr (k3-C₂₄H₂₉NO₂) Cl] (complex 1) has been investigated according to gravimetric, IR and NMR spectral and GPC analysis of the resulting poly(cyclohexene carbonate) polymers (PCHC). Typical copolymerization reactions were carried out in bulk CHO monomer, utilizing a 25 ml stainless steel autoclave reactor, pressurized to 52 bar in CO₂ and maintained at 80 °C. Complex 1 proved to be selective toward production of polymer and exhibited an average turnover frequency of TOF = 12.8(±1.1) hr-1. Nevertheless, limited CO₂ incorporation was observed, resulting in polymers that were ~40-50% polycarbonate at most. Introduction of a neutral phosphine (tricyclohexylphosphine, PCy₃) was observed to increase CO₂ incorporations to as high as 82% based on 1H NMR analysis. GPC analysis showed the polymers exhibited number-average-molecular-weights with a mean value of Mn= 2.6(±0.4) kDa under optimal copolymerization conditions (with 1 equivalent PCy₃relative to chromium) and fairly broad molecular weight distributions with polydispersity indices (PDI) ranging from 3.6 to 12.0.

Keywords: CO₂Capture; CO₂Utilization; CO₂Epoxide Copolymerization; Polycarbonate; Homogeneous Catalysis

Abbreviations: CO₂: Carbon Dioxide; CHO: Cyclohexene Oxide; H₂L: (1S,2R)-1-[(3,5-di-tert-butyl salicylidine)imino]-2-indanol; H₂L’: 1-[(3-tert-butyl-5-bromosalicylidine)imino]-2-indanol; TOF: Turnover Frequency; PCHC: Poly(cyclohexene carbonate); PCy₃: Tricyclohexylphosphine; PDI: Polydispersity Index

Abstract| Introduction| Materials and Methods| Results and Discussion| Conclusion| Acknowledgement| Conflicts of Interest| References|