CO2-releasing blowing agents from modified polyethylenimines slightly consume isocyanate groups while foaming polyurethanes

Abstract

Carbon dioxide adducts from polypropylene glycol (PPG)-grafted polyethylenimines (PEIs) are promising alternatives to the traditional, climate-changing blowing agents for polyurethanes (PUs). Their commercialization is hindered by the fact that they can restore their original polyamine structure when releasing CO2 to blow PUs and that the extent to which the restored amine groups react with the isocyanate (NCO) groups in the foaming mixture is still not clear. The extent of this reaction was quantitatively investigated by FTIR and 1H NMR spectroscopy. The increase in the PPG side chain length or in the grafting rate reduced the reaction extent of the restored amines due to increased steric hindrance. The increase in the PEI backbone molecular weight decreased the macromolecular mobility, which somewhat inhibited a full contact between the restored amine groups and the NCO groups and thus caused a decrease in the reaction extent as well. Overall, the reaction extents of the blowing agent amine groups, ranging from 0.4% to 1.5%, were too low to change the foaming process chemically. In conclusion, these CO2-releasing blowing agents can be technically regarded as physical blowing agents.