Preparation of rigid polyurethane foams catalyzed by copper-amine complexes in ethylene glycol

Abstract

Copper-amine complex catalysts for rigid polyurethane (RPUR) foam preparation were synthesized, when used, the catalysts were dissolved in ethylene glycol in order to improve its solubility in foam formulation. Copper-amine complex catalysts, namely Cu(X)₂(en)₂, Cu(X)₂(trien), Cu(X)₂(tetraen) and Cu(X)₂(pentaen) (where X= OAc, acac, NO₃, Cl; en = ethylenediamine, trien = triethylenetetramine, tetraen = tetraethylenepentamine and pentaen = pentaethylenehexamine) were synthesized using ethylene glycol as a solvent. The synthesized complexes were characterized by UV-visible spectroscopy and mass spectrometry. RPUR foams were prepared from the reaction between polymeric 4,4' methane diphenyl diisocyanate and polyether polyol. The catalytic activity was compared with a commercial catalyst, N,N-dimethylcyclohexylamine (DMCHA), by investigation of reaction times, physical and mechanical properties of foams. ATR-IR spectroscopy was used to determine isocyanate (NCO) conversion of foams. It was found that the suitable catalyst concentration was 30%wt in ethylene glycol. Among all complexes, Cu(OAc)₂(en)₂, Cu(OAc)₂(trien), Cu(OAc)₂(tetraen), Cu(OAc)₂(pentaen) and Cu(acac)₂(en)₂ showed comparable catalytic activity to DMCHA. Cu(OAc)₂(trien) was the best catalyst because it showed high catalytic activity and gave appropriate foam appearance.