Phenylene-containing polyethylenimine-like polymers absorb and release CO2 to blow biomass-based polyurethanes

CO₂ adducts of hydrophobically modified polyethylenimines (PEIs) are promising alternatives to global warming halogen-containing blowing agents of polyurethanes (PUs), despite the high cost of the raw material PEIs. Herein, an economical synthesis of PEI-like polymers was explored via condensation between pentaethylenehexamine and terephthalaldehyde, followed by chemical reduction of the as-formed Schiff base linkages. The resultant p-phenylene-containing polyamine polymers (PEIPs) could be grafted with alkyl (C_n) side chains and adducted with CO₂ to form a new type of CO₂-releasing blowing agents for PUs designated as yC_n-xPEIP-CO₂s, where x and y represent the backbone molecular weight and the side chain grafting rate, respectively. Among them, the specimen 10%C₈−3.6 kPEIP-CO₂ was the most effective in terms of good dispersibility in PU raw materials, low foam density (about 51 kg/m³), and uniform pore morphology. Moreover, the phenylene linkages enhanced the hydrophobicity of the consequent CO₂ adducts and weakened the intermolecular hydrogen bonding and ionic attraction, both facilitating the dispersion of the corresponding blowing agents into a castor oil-derived polyol, Polycin M-365. The specimen 10%C₈−3.6 kPEIP-CO₂ could disperse as suspended fine floccules that finally aggregated into a flocculent, liquid-like bottom layer, being easily redispersed into the bulk. The unique compatibility with plant oil-derived polyols and the economic availability would make the PEIP-based blowing agents suitable for the next generation of sustainable and biomass-based PU foams.