Tapered Multiblock Copolymers Based on Isoprene and 4-Methylstyrene: Influence of the Tapered Interface on the Self-Assembly and Thermomechanical Properties

The synthesis of tapered multiblock copolymers by statistical living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in cyclohexane is based on vastly different reactivity ratios of I and 4MS (rI = 25.4 and r4MS = 0.007). A library of tapered multiblock copolymers was prepared with different molecular weights (approximate molecular weights of 80, 240, and 400 kg/mol) and number of blocks (P(I-co-4MS)n with 1 ≤ n ≤ 5), and their thermomechanical properties were investigated by differential scanning calorimetry, rheology, and tensile testing in relation to their nanodomain structure, the latter investigated by small-angle X-ray scattering. The interaction parameter between I and 4MS segments was obtained based on the order-to-disorder transition temperatures of a series of PI-b-P4MS diblock copolymers prepared by sequential addition of monomers. The obtained χ(T) dependencies (χMFT = 23.2/T – 0.024 and χFH = 36.0/T – 0.041) are weaker than in the corresponding PI-b-PS system,...