9. A Systematic Series of ‘Model’ PTMO Based Segmented Polyurethanes Reinvestigated Using Atomic Force Microscopy

9.1 Chapter Summary Approximately thirty years after their preparation, the nanoscale morphology of a series of ‘model’ segmented polyurethane elastomers has been further elucidated using the technique of tapping mode AFM. The materials investigated are based on 1,4-butanediol extended piperazine based hard segments and employ poly(tetramethylene oxide) soft segments. The chemistry of these polyurethanes was specifically controlled in a manner which yielded monodisperse hard segments precisely containing either one, two, three, or four repeating units. Phase images obtained via AFM, for the first time, enable visual representation of the microphase separated morphology of these materials. AFM images also confirmed the presence of a spherulitic morphology, as shown several years ago using SALS and SEM. In addition, using AFM, the hard domains were found to preferentially orient with their long axis along the radial direction of the spherulites. The hard domain connectivity was found to increase with increasing percentage hard segment content of the polymers.