Preparation of polyurethane and polyisocyanurate foams catalyzed by metal acetate-ammonia complexes

Abstract

Metal acetate-ammonia complex solutions, namely Cu(Amm) and Zn(Amm), were synthesized and characterized by UV-visible spectroscopy and MALDI-TOF mass spectrometry. Cu(Amm) and Zn(Amm) were used as homogeneous catalysts for accelerating gelling (urethane formation) and blowing reactions (CO2 generation) of rigid polyurethane (RPUR) and polyisocyanurate (PIR) foams. Potassium octoate solution in diethylene glycol, which was used as a trimerization catalyst, was mixed with Cu(Amm) or Zn(Amm) to give a catalyst mixture which can catalyze gelling, blowing and trimerization reactions for the preparation of PIR foams. The catalytic activity of Cu(Amm) and Zn(Amm) in gelling and blowing reactions was compared to that of N,N-dimethylcyclohexylamine (DMCHA), which is an industrial catalyst, and studied by density functional theory (DFT) method, which revealed that Cu(Amm) and Zn(Amm) were Lewis acid catalysts and could decrease the activation energy, but increase the rate constant of gelling and blowing reactions. Cu(Amm) had higher catalytic activity, while Zn(Amm) had lower catalytic activity than DMCHA. Cu(Amm) gave rigid PUR foams with comparable density, % isocyanate conversion and compression strength to those of DMCHA. PIR foams prepared from the mixtures of potassium octoate solution with Cu(Amm) or Zn(Amm) at isocyanate index of 200 had better compression strength, fire-retarded properties and thermal stability than their relating rigid PUR foams. These PIR foams were the ductile materials which had higher compression strength and did not rupture during the compressing test in comparison to the PIR foam prepared from the mixture of potassium octoate solution with DMCHA.