(122e) Synthesis and Characterization of Multiblock Copolymers with Urethane Links
Multiblock copolymers containing 10 or more blocks are expected to have unique morphologies and mechanical properties relative to conventional triblocks. Poly(styrene-b-butadiene) (PS-PB) multiblock copolymers were synthesized using a combination of anionic polymerization and urethane based condensation reactions of dihydroxyl PS and PB. Two types of block sequences were prepared, one with random and the second with alternating PS and PB block architectures. These block copolymers were characterized with 1H-NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC), demonstrating efficient block coupling of blocks and overall polydispersities close to the anticipated most probable distribution. Morphologies were examined using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). In all instances the multiblock copolymers contained a microphase separated bicontinuous structure regardless of composition or sequencing. Tensile tests revealed that the PS–PB multiblock copolymers are tougher than the corresponding linear PS–PB–PS triblock copolymers at similar molecular weight and composition.