Characterization of polyethylenes produced in supercritical carbon dioxide by a late-transition-metal catalyst

The coordination polymn. of ethylene with a palladium-based catalyst is studied using supercrit. carbon dioxide (scCO2) as a reaction medium at different temps., pressures, and ethylene concns. Addnl., the polymn. is performed in dichloromethane as a ref. The polymers are analyzed with gel permeation chromatog. (GPC), differential scanning calorimetry (DSC), and hydrogen and carbon NMR (1H and 13C NMR). The polymns. in scCO2 and dichloromethane result in highly branched amorphous polymers of high mol. wt. and narrow mol. wt. distributions. Although the polymn. in scCO2 is a pptn. polymn., the obtained results are similar to the polymn. in dichloromethane, which is a soln. polymn. 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 range investigated, temp. and ethylene concn. have an effect on the mol. wt. of the polymer, however, not on the SCB of the polymers. Furthermore, anal. of the 13C NMR spectra of the polyethylenes gives a strong indication of a new branch-on-branch structure, which has not been assigned before