Molecular Structure of the Hard Segments in Flexible Foams

The main basis of structure-property-relationships of polymeric materials is a good characterization of the structure under study. Such is the case for cross linked polyurethanes such as flexible foams. To overcome the problems of solubility of these materials, a selective degradation process was used, leaving the hard segments unaffected. These were then analyzed by MALDI-TOF (Matrix Assisted Laser Desorption-Ionization Time of Flight mass spectrometry). Using these techniques, the length distribution of the hard segments was examined. It was found that the length of the hard segments decreases much slower for polyester foams than for polyether foams. This fact was attributed to a lower solubility of the hard segments in polyethers, which leads to an earlier onset of phase separation. Thus, both mobility and reactivity of the segments in the segregated hard domains are reduced. This fact also explains why the length of the hard segments is only slightly dependent on the water content, or the index, at least in polyether foams. Chemical differences such as the incorporation of polymeric MDI or reactive catalysts could also be shown. Furthermore, this work shows for the first time that presence of cyclic hard segments could be established in a foam.