Abstract: The micromorphology of segmented polysiloxane-polyureas based on polydimethylsiloxane or polycyanopropyimethylsiloxane soft segments and semicrystalline methylene diphenylene diiso-cyanate and diethyleneamine hard segments was examined using transition electron microscopy(TEM) and small angle X-ray scattering (SAXS).Specimens for eletron microscopy studies were prepared by thin film casting.The spherical morphology was observed in all of the samples.The size of the hard domain of polycyanopropylsiloxane polyurea is smaller and more regular than that of polydimethylsiloxane polyurea.The micrcdomain spacings and the size of the poiyurea hard segment measured by TEMwere compared to the results calculated from SAXSdata.It is also found that there are two steps In the accumulation of the hard domains.At the first step, a few polyurea aggregate by hydrogen bond to form the ''fundamental particles".In the second step, these "fundamental particles" gathered up together further to form the hard mierodomains.The slower evaporation rates of the solvents caused the larger polyurea mierodomains.

Key words: Polysiloxane, Polyurea, Phase separation, Segmented copolymer