Influence of Modified Hexamethylene-diamine on the Properties of Polyurea

Novel sterically hindered chain extender, diacetyl hexamethylene-diamine (MHAD) was synthesized by acetylating hexamethylene-diamine (HAD) with glacial acetic acid in presence of phosphoric acid, in order to reduce high reactivity of synthesizing polyurea and improve its properties. Chemical structures of modified HAD was confirmed through FTIR, the determination of the nitrogen content, High resolution ESI-FTICR mass spectrometry and ¹H-NMR analysis. The results of measuring its melting stages showed that purity of the product was better. Polyureas were synthesized by two-step solution process of 4,4´-diphenyl diisocyanate(MDI) and amine terminated polyether (Jeffamine D-2000) with different chain extenders. The influence of modified HAD on gel time of the polyurea was investigated. The gel time was prolonged, that is, the reaction activity was decreased when MHAD was used as chain extenders instead of HAD. Thermal stability of polyureas was not affected, and its mechanical properties were heightened remarkably.