Carbon dioxide adduct from polypropylene glycol grafted polyethyleneimine as a climate-friendly blowing agent for polyurethane foams

Abstract

A novel CO2 adduct has been synthesised from a branched polyethyleneimine with polypropylene glycol (PPG) side chains and can serve as an alternative to traditional polyurethane blowing agents, such as hydrochloroflourocarbons and hydrofluorocarbons, which cause ozone depletion and/or global warming. The CO2 adduction trapped 13.8 wt% of CO2, forming alkylammonium carbamates in the main chains. Therefore, the prepared blowing agent is amphophilic, and can form micellae-like spheres in the mixture of polyurethane raw materials called the white component. Once this mixture is blended with isocyanate or the black component like in conventional foaming processes, the consequent exothermic polymerisation drives the release of the captured CO2 from the micelles, serving as the foaming gas. Meanwhile, the blowing agent gradually restores its original polyamine structure, whose bulky PPG side chains can sterically inhibit the reaction between the restored amine groups and the isocyanate groups in the growing polyurethane chains. The resulting foam displays uniform cellular morphology with a much lower density than the control sample blown by trances of water from the raw materials. This is the first report using thermally instable CO2 adduct to blow polyurethanes, which could pave the way for the next generation of climate-friendly polyurethane blowing agents.