Polybutadiene-based polyurethanes with controlled properties: Preparation and characterization

A series of segmented polyurethanes was prepared from the new commercial pr oduct KRASOL LBH (linear liquid polybutadiene terminated with secondary hyd roxy groups), aromatic diisocyanates, and an aliphatic low-molecular-weight diol. Three types of networks were prepared, with the nature of the crossl inks varied from purely chemical to physical, with a continuous transition to "combined" networks containing both crosslink types. Potassium 2-ethyl h exanoate was used as a catalyst of the ill situ formation of trifunctional isocyanurate groups (by cyclotrimerization of isocyanate groups). It was co nfirmed that mechanical, thermal, and swelling properties are considerably influenced by the ratio of chemical to physical crosslink concentration. Th e best balance of stress-strain properties was obtained for "combined" netw orks at a NCO-OH molar ratio of 1.10 when only a few chemical crosslinks ar e present in predominantly physically crosslinked networks. The presence of thermally stable isocyanurate groups mainly influences the storage shear m odulus at elevated temperatures. Small-angle X-ray scattering confirmed the two-phase structure of polyurethanes with a periodicity of 6-8 nm. (C) 200 0 John Wiley & Sons, Inc.