Chain Architecture as an Orthogonal Parameter To Influence Block Copolymer Morphology. Synthesis and Characterization of Hyperbranched Block Copolymers: HyperBlocks

Abstract

For block copolymers there is usually a strong correlation between the copolymer composition (volume fraction of each block) and the resulting solid state morphology. However, for a variety of potential applications, e.g., semipermeable membranes or templates, it might be desirable to vary the microphase morphology independently of copolymer composition. The use of chain branching is an additional and orthogonal parameter to influence morphology, independently of composition, and we explore for the first time the impact of a long-chain, hyperbranched architecture on the microphase-separated, solid state morphology of branched block copolymers. To this end, a series of functionalized linear ABA (polystyrene–polyisoprene–polystyrene) triblock copolymers (macromonomers), hyperbranched ABA triblock copolymers (HyperBlocks), and blends of HyperBlocks with a commercially available linear ABA triblock copolymeric thermoplastic elastomer were prepared. Moreover, the “macromonomer” approach is the only feasible route to prepare hyperbranched block copolymers. The solid state morphology of the resulting materials was investigated by a combination of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) which showed a dramatic impact of the chain architecture on the resulting morphology. While the linear ABA triblock copolymers showed the expected microphase-separated morphology with long-range order dependent upon composition, no long-range order was observed in the HyperBlocks. Instead, the HyperBlocks revealed a microphase-separated morphology without long-range lattice order, irrespective of macromonomer composition or molecular weight. Furthermore, when HyperBlocks were subsequently blended with a commercially available linear ABA triblock copolymer (Kraton D1160), the HyperBlock appeared to impose a microphase-separated morphology without long-range lattice order upon the linear copolymer even when the HyperBlock is present as the minor component in the blend at levels as low as 10 wt %.