Characterization of Polyethylenes Produced in Supercritical Carbon Dioxide by a Late-Transition-Metal Catalyst

Abstract

The coordination polymerization of ethylene with a palladium-based catalyst is studied using supercritical carbon dioxide (scCO2) as a reaction medium at different temperatures, pressures, and ethylene concentrations. Additionally, the polymerization is performed in dichloromethane as a reference. The polymers are analyzed with gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and hydrogen and carbon nuclear magnetic resonance (1H and 13C NMR). The polymerizations in scCO2 and dichloromethane result in highly branched amorphous polymers of high molecular weight and narrow molecular weight distributions. Although the polymerization in scCO2 is a precipitation polymerization, the obtained results are similar to the polymerization in dichloromethane, which is a solution polymerization. Moreover, the polymers produced in scCO2 show a higher degree of short chain branching (SCB), which likely originates from the nonpolar environment compared to the polar dichloromethane. Within the ...