A mass spectrometry analysis of hard segment length distribution in polyurethanes

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry was utilized to determine the hard segment length distribution in poly(urea-urethane)s. Although hard segment length is expected to vary with water content in the initial formulations, the actual distribution is rather similar for all samples analyzed. A more detailed analysis, however, revealed that the principal difference is in the region corresponding to hard segments with greater than eight urea repeat units. This finding has implications for both in the origin of phase separation behavior and the mechanical performance of phase separated heterogeneous polymers. The similarity in hard segment distribution suggests that phase separation behavior in these polyurethane foams cannot be due solely to the orientational entropic contribution. The presence of these long hard segments, although not extensive (7% of the total number fraction), may contribute significantly to mechanical performance. MALDI also revealed the presence of side products. The amount of cyclic species, either isocyanurate or cyclic hard segments, varied from 2 to 4% for foams with different urea contents.