Polybutadiene-Based Polyurethanes with Controlled Properties: Preparation and Characterization MILENA S ˇ PI ´ RKOVA ´ , 1 LIBOR MATE ˇ JKA, 1 DRAHOMI ´ RA HLAVATA ´ , 1 BOHUMIL MEISSNER, 1 JINDR ˇ ICH PYTELA 2 1 Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic 2 Kauc ˇuk, a.s., Synthetic Rubber Research Institute, 278 52 Kralupy nad Vltavou, Czech Republic ABSTRACT: A series of segmented polyurethanes was prepared from the new commercial product KRASOL LBH (linear liquid polybutadiene terminated with secondary hydroxy groups), aromatic diisocyanates, and an aliphatic low-molecular-weight diol. Three types of networks were prepared, with the nature of the crosslinks varied from purely chemical to physical, with a continuous transition to “combined” networks containing both crosslink types. Potassium 2-ethyl hexanoate was used as a catalyst of the in situ formation of trifunctional isocyanurate groups (by cyclotrimerization of isocyanate groups). It was confirmed that mechanical, thermal, and swelling properties are considerably influenced by the ratio of chemical to physical crosslink concentration. The best balance of stress– strain properties was obtained for “combined” networks at a NCO–OH molar ratio of 1.10 when only a few chemical crosslinks are present in predominantly physically crosslinked networks. The presence of thermally stable isocyanurate groups mainly influences the storage shear modulus at elevated temperatures. Small-angle X-ray scattering confirmed the two-phase structure of polyurethanes with a periodicity of 6 – 8 nm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 381–389, 2000 Key words: polyurethanes; polybutadiene diol; isocyanurate groups; mechanical properties; SAXS INTRODUCTION Segmented polyurethanes (PURs) are important commercial materials distinguished for the in- compatibility of their soft (macrodiol) and hard (diisocyanate and chain extender, i.e., low-molec- ular-weight diol or diamine) segments. The hard segments aggregate to form glassy or crystalline hard-segment domains in the soft matrix. 1 The main factors influencing the phase separation in- clude the type and segment length, crystallizabil- ity, tendency for soft segment– hard segment hy- drogen bonding, sample composition, and history of the sample preparation. 2–4 Hard-segment domains act as physical junc- tion points, greatly improving mechanical proper- ties of PUR networks. 3 The tensile strength var- ies with the content of the hard segments and mainly grows up to the optimum. 3,5–7 Chemically crosslinked polyurethanes are formed if a tri- or higher-functional compound is present in the system. Compared to physical net- works, they are distinguished for better shape memory and better thermal stability (they do not flow at elevated temperature unless chemical deg- radation occurs), but their ultimate mechanical properties are limited (an increase in modulus and often stress at break are accompanied by a considerable decrease in elongation at break, as the reorganization of chains is reduced because of covalent bonds). Triols are mostly used as cross- linking agents, but it is also possible to utilize a tri- or higher-functional isocyanate component, for instance, to cyclotrimerize the isocyanate groups Correspondence to: M. S ˇ pı ´rkova ´ (spirkova@imc.cas.cz). Contract grant sponsor: Academy of Sciences of the Czech Republic; contract grant number: 12-96-K. Journal of Applied Polymer Science, Vol. 77, 381–389 (2000) © 2000 John Wiley & Sons, Inc. 381