Effect of Segregation Strength on Mesophase Separation in Statistical Multiblock Copolymers Synthesized through a High-Throughput Experimentation Approach

Ethylene/hex-1-ene (E/H) statistical multiblock copolymers (MBCs) with molecular mass between 144 and 188 kDa, and segregation strength greater than that of commercially available samples, are prepared in a high-throughput parallel pressure reactor via chain shuttling copolymerization technology (CSC). They are characterized by alternation of crystalline (hard) and amorphous (soft) blocks with H content xH of ≈1 and ≈34 mol % (ΔxH ≈ 33 mol %), respectively, hard block content wh ≈ 20, 30, 35, and 50 wt %, and a statistical distribution of block length and the number of blocks per chain. Transmission electron microscopy shows mesophase-separated morphologies in the solid state, crystallization of hard blocks in separated domains, and only scarce inclusion of hard blocks in the alien domains rich in soft blocks. MBCs with hard block content wh equal to ≈20 and 30 wt % show round-shaped and isolated worm-like domains rich in hard blocks, respectively, separated by the surrounding amorphous phase through sharp boundaries. The sample with wh ≈ 35 wt % shows a disordered bicontinuous structure, whereas the sample with 50 wt % gives rise to an inverted morphology, characterized by round-shaped domains rich in soft blocks scarcely crossed by lamellar crystals and surrounded by a matrix containing sheaf-like lamellar crystal aggregates splaying in all directions. Rheological measurements carried out in a linear viscoelastic regime reveal time-temperature superposition failure in the measured frequency range, suggesting that mesophase separation occurs already in the melt. Mesophase separation in the melt and solid state is controlled by the blocks of major length that are characterized by high segregation strength. The partial solubility of the hard blocks with minor length in the soft block-rich regions is instead responsible for the sporadic crystallization of lamellar crystals in the alien domains.