Zinc glutarate-mediated copolymerization of CO2 and PO – parameter studies using design of experiments

Abstract

The copolymerization of carbon dioxide (CO₂) with propylene oxide (PO) mediated by a nanoscopic zinc glutarate (ZnGA) catalyst was systematically analyzed using a design of experiments approach. The influence of the reaction temperature, CO₂-pressure and reaction time on the catalyst's activity, the polymer composition and the molecular weight was determined. The empirical models obtained allow accurate predictions of the output parameter within the design space. The best catalyst performance in terms of polymer yield and CO₂ incorporation was observed at molar fractions of x(CO₂) ≈ 0.3 in the feed. The highest productivities were observed at 70–80 °C and pressures between 3.5 and 4.0 MPa. The copolymerization in bulk initially shows a “pseudo-living” behavior until M_n reaches a threshold of about 80 kDa. The polymerization rate at higher conversions seems to be limited too, possibly by the initiation of new chains; catalyst deactivation over time was excluded. The high PDI values at early reaction stages indicate that the initiation reaction is the rate-determining step.