Synthesis and properties of polyurethanes based on polyolefine: 1. Rigid polyurethanes and amorphous segmented polyurethanes prepared in polar solvents under homogeneous conditions

Abstract

Pure hard-block polyurethanes and amorphous segmented hydrogenated polybutadiene (H.PBD)-based polyurethanes have been synthesized under homogeneous conditions in solution. All amorphous semi-crystalline pure hard blocks show a glass transition temperature, T g, detected by differential scanning calorimetry (d.s.c.), depending on the nature of the diisocyanate and of the chain extender. Segmented amorphous H.PBD polyurethane exhibits two glass transitions: a soft phase T g(S) and a hard phase T g(H). Thermal treatments show rearrangements in the two-phase materials. Quantitative evaluation of phase separation, as determined by the heat capacity change, ΔC p(S), at the glass transition of the soft phase, T g(S), shows that the phase separation of the soft segments is in the range 85–95%. These particular non-polar soft segments force the polar hard segments in the hard phase to be well organized due to inter-urethane hydrogen bonding, which produces a higher T g(H) in the segmented polyurethanes than the T g of the pure hard blocks. The morphology of such polyurethanes with non-polar soft segments can be well characterized by dielectric measurements. Dielectric spectroscopy is in good agreement with d.s.c. results. A third transition between the soft and hard phase transitions has been detected. This relaxation is attributed to the mixed interfacial region. Increasing the hard-segment content increases this interfacial region.