Diacetyl hexamethylene-diamine (MHAD) and diacetyl m-phenylenediamine (Mm-PDA) were synthesized by acetylating hexamethyene-diamin (HAD) and m-phenylenediamine (m-PDA) with glacial acetic acid in presence of phosphoric acid, in order to retard the high reactivity of polyurea. Chemical structures of modified diamine chain extenders were confirmed through FTIR, the determination of the nitrogen content, High resolution ESI-Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry and (1)H-NMR analysis. Polyureas were synthesized via two-step solution process by reaction of 4,4'-diphenyl diisocyanate (MDI), amine terminated polyether (Jeffamine D-2000) with different chain extenders. The influence of modified diamine chain extenders on gel time of polyurea was investigated. The gel time was prolonged from 11s to 52s and 13s to 65s respectively. The reaction kinetics of synthesizing polyureas were studied by FTIR. The results showed that extending reaction with MHAD was second order kinetic mechanism, its apparent activation energy was 43.99 kJ.mol(-1); extending reaction with Mm-PDA reaction was first order, its activation energy was 58.95 kJ.mol(-1). (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 479-484, 2012