Abstract: A series of waterborne polyurethanes(WPU) were prepared from isophorone diisocyanate(IPDI) and dimethylolpropionic acid(DMPA),which acted as the hard segment.Effects of the hard segment content on the emulsion stability,thermostability and mechanical properties of WPU had been studied.When the mass fraction of the hard segment was below 26%,the emulsion stability was poor.With the increase of hard segment content,the tensile strength of the resultant film prepared from WPU increased quickly,and the breaking elongation decreased slightly;FTIR spectra showed that the intensity of free N——H stretching vibration peaks dropped,while the intensity of hydrogen bonded N——H stretching vibration peaks increased.At the same time,the peak shape of C=O stretching vibration changed obviously and shifted to lower wave numbers.It is shown that the hydrogen bonds disaggregated evidently and the intensity of endothermic peak strengthened from 50℃ to 125℃ according to DSC analysis,suggesting that the hydrogen bonding strengthened gradually as the hard segment content increased.The TG curves indicated that the thermal decomposition of WPU was mainly a step-by-step decomposition of the hard and soft segments.The decomposition temperature of the hard segment and the thermostability of WPU decreased with the increase of hard segment content.