Synthesis, Structure, and Properties of Alternating and Random Poly(styrene‑<i>b</i>‑butadiene) Multiblock Copolymers

We report a synthetic method for the preparation of well-defined poly­(styrene-<i>b</i>-butadiene) (PS-PB)_<i>n</i> multiblock copolymers using a combination of living anionic polymerization and urethane based polycondensation along with an assessment of the associated microphase morphology and thermal and mechanical properties. The prepolymers, <i>α,ω</i>-dihydroxy polystyrene (HO-PS-OH) and <i>α,ω</i>-dihydroxy polybutadiene (HO-PB-OH), were prepared using a protected initiator, followed by deprotection and condensation with isophorone diisocyanate (IPDI) leading to the (PS-PB)_<i>n</i> multiblock copolymers. Two types of block sequences were generated, one with random block sequences (PS-ran-PB)_<i>n</i> and the second with alternating (PS-alt-PB)_<i>n</i> block architectures. Size exclusion chromatography (SEC), ¹H nuclear magnetic resonance (NMR), and Fourier transform infrared spectrometry (FTIR) confirmed that the synthetic procedures yielded the desired products. Differential scanning calorimetry (DSC) revealed microphase separation and small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) demonstrated that the multiblock materials, containing between 69% and 85% by volume glassy PS, are characterized by a disordered bicontinuous-like morphology. Tensile tests demonstrated yielding followed by necking and an overall ductility that translates into much greater toughness than that typically found in glassy continuous SBS triblock copolymers