Synthesis and properties of polyurethanes based on polyolefin: 2. Semicrystalline segmented polyurethanes prepared under heterogeneous or homogeneous synthesis conditions

Abstract

Semicrystalline segmented polyurethanes based on hydrogenated polybutadiene (H-PBD) soft segments and butanediol (BDO) or di-β-hydroxyethyl hydroquinone (HQEE) as chain extenders were synthesized under different homogeneous or heterogeneous conditions, in solution or in bulk. Segmented semicrystalline H-PBD polyurethanes exhibit two glass transitions: a soft-phase transition T g(S) and a hard-phase transition T g(H). Thermal treatments show rearrangements in the two-phase materials. The dielectric relaxations, α S and α H, confirm the thermal behaviour and also the presence of a mixed interfacial region ( α′ H). Increasing the hard-segment content increases this mixed-phase relaxation. This effect is also observed in the polyurethanes prepared in bulk instead of in solution, because of the decrease in the segregation ratio of the soft segments. Bulk samples also contain short isolated or amorphous hard segments as shown by size exclusion chromatography results and the conduction process appearing in the dielectric measurements. Such different routes of preparation induce various characteristics and tensile properties of the corresponding polyurethanes attributed mainly to premature phase separation occurring during the polymerization and the competition between the phase separation rate and the polymerization rate.