Copper–amine complexes as new catalysts for rigid polyurethane foam preparations

A new class of catalyst for the preparation of rigid polyurethane (RPUR) foams was developed. Metal(II)–amine complexes [M(en)2 and M(trien), where M = Cu or Ni, en = ethylenediamine, and trien = triethylenetetramine] were synthesized and used as catalysts in the preparation of RPUR foams. The catalytic activity of the metal(II)–amine complexes and properties of the RPUR foams were investigated and compared to those prepared by N,N‐dimethylcyclohexylamine (DMCHA), which is a common commercial tertiary amine catalyst used in the preparation of RPUR foams. The use of M(en)2 and M(trien) can improve the working environment in RPUR foam processing because DMCHA and other commercial tertiary amine catalysts have a strong odor, whereas M(en)2 and M(trien) do not have any odor. The reaction times in RPUR foam preparation, namely, cream time, gel time, tack‐free time, and rise time, were investigated. These data indicated that the copper–ethylenediamine complex [Cu(en)2] and copper–triethylenetetramine complex [Cu(trien)] had comparable catalytic activity to DMCHA, whereas the catalytic activity of the nickel complexes was not good. Attenuated total reflection–IR spectroscopy of the RPUR foams prepared with Cu(en)2 and Cu(trien) showed quantitative isocyanate (NCO) conversion. The density and compressive strength of the RPUR foams prepared from Cu(en)2 and Cu(trien) were comparable to those prepared from DMCHA.