| In this study butadiene-isoprene-butadiene (BIB) triblocks were synthesized anionically, and the 1,4-polybutadiene blocks were subsequently selectively hydrogenated using a coordination catalyst (cobalt octoate/n-BuLi). It was necessary to find the proper conditions for good hydrogenations (> 99% hydrogenation) with minimal degradation (< 3% chain scission).; Hydrogenated 1,4-polybutadiene homopolymer was also prepared, and its mechanical properties were found to be close to those of low-density polyethylene (LDPE).; Three such hydrogenated triblock polymers (HBIB) with varying compositions were prepared in order to study the structure-property relationships of ABA thermoplastic elastomers with crystallizable end blocks. The super-structure, i.e., spherulitic structure, was observed in the optical microscope, and the domain morphology was studied with a transmission electron microscope. The properties were studied by cyclic tensile deformation as well as continuous uniaxial tensile elongation. The thermal properties and the crystal melting behavior were also studied. The rheology of these materials was characterized by dynamic viscosity measurements.; The hydrogenated polybutadiene end blocks crystallized quantitatively as determined by heat of fusion measurements, independent of polymer composition, although the polyisoprene blocks reduced spherulite formation. The hydrogenated polybutadiene phase separated into crystalline domains which apparently acted as "filler" particles as well as crosslinks. The crystalline domains deformed tensile elongation resulting in stress softening, permanent set, and hysteresis.; The presence of imperfect crystals was observed in the DSC thermograms of these triblocks and made the thermal properties of the polymer more sensitive to temperature than their styrene-isoprene-styrene (SIS) counterpart.; The rheological properties of these triblocks at 250,000 total molecular weight exhibited viscosity behavior typical of systems in which a two-phase system persists in the melt due to incompatibility between the blocks. |
