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

Abstract CO 2 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 CO 2 to form a new type of CO 2 ‐releasing blowing agents for PUs designated as yC n ‐ x PEIP‐CO 2 s, where x and y represent the backbone molecular weight and the side chain grafting rate, respectively. Among them, the specimen 10%C 8 −3.6 kPEIP‐CO 2 was the most effective in terms of good dispersibility in PU raw materials, low foam density (about 51 kg/m 3 ), and uniform pore morphology. Moreover, the phenylene linkages enhanced the hydrophobicity of the consequent CO 2 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%C 8 −3.6 kPEIP‐CO 2 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.