Nitrogen-based curing agents

Shao, C. H., Huang, J. J., Chen, G. N., Yeh, J. T., and Chen, K. N., Thermal and combustion behaviors of aqueous-based polyurethane system with phosphorus and nitrogen containing curing agent, Polym. Degrad. Stab., 1999, 65, 359-371. 

The rate of cure of epoxy resins with tertiary amines depends primarily upon the extent to which the nitrogen is sterically blocked. The homopolymerization reaction depends on the temperature as well as the concentration and type of tertiary amine. Benzyldimethylamine (BDMA) and TDMAMP are mainly used as accelerators for other curing agents, in the cining of anhydride-and dicyandiamide-based systems. Other tertiary amine catalysts include 1,4-diazabicyclo(2,2,2)octane (DABCO) and diazabicycloundecene (DBU). 

The reaction was carried out at 100°C for about two hours until the theoretical isocyanate content, as determined by the di-n-butylamine titration method (27), was reached. The PU prepolymer with or without tertiary amine nitrogen groups was dissolved in dry MEK to obtain a prepolymer solution of 30-40% solids. It was then mixed with a mixture of 1,4-BD/TMP (4 1 by equiv. ratio) at an NCO/OH = 1.05/1.0 ratio in the presence of T-12 catalyst (0.05% based on total weight). The reaction mixture was cast in a metal mold treated with a release agent at ambient temperature. After standing 3-5 hours at room temperature, the mold was placed in an oven and post-cured at 100°C for 16 hours. The samples were then conditioned in a desiccator for one week before testing. 

Expanded materials with excellent high-temperature properties are obtained when cresol novolacs are used as hardeners. A typical formulation is based on mixtures of bisphenol A resins and epoxy novolac resins which are cured by cresol novolacs and accelerated by suitable nitrogen-containing agents. 

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