Effect of soft segment length and chain extender structure on phase separation and morphology in poly(urethane urea)s

The phase separation and morphology in poly(urethane urea)s were investigated as soft-segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of E"(max) and tan delta(max) to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase-separated domains. The hard domains were in the form of spheres 5-10 nm, or long needles 5 nm thick and 50-300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.