ABSTRACT
Block copolymers have fascinated polymer scientists for over half a century due to their potential in the development of commercially viable materials with controlled physical properties resulting from their ability to self-assemble into periodic structures with domain spacings on the order of exciton diffusion (~10–100 nm) (Bates, 1991). These materials are composed from two or more chemically different polymer blocks that are covalently-bonded together. The nanoscale assembly and macroscale behavior of these materials are primarily determined by the segment-segment interaction parameters (χ ij), component volume fractions (f i), and molecular weight (N) of the individual polymer chains (Epps III and O’Reilly, 2016). Thus, it is possible to alter the properties of a block copolymer by varying the size, type, and placement of the various components. Unfortunately, the unique physical properties of block copolymers cannot be duplicated through simple blending of non-bonded polymer blocks. Thus, the development of methods for the synthesis of these complex macromolecules are required to realize their full potential. The numerous methods for the synthesis of well-defined, near monodisperse non-conjugated “coil” polymers has enabled the synthesis of a plethora of coil-coil block copolymers with diverse compositions (Bates and Bates, 2017; Koo et al., 2013). As a result of the rheological investigations of these systems, the behavior of block copolymers made from traditional coil-coil polymers is well understood. In contrast, the synthesis of well-defined conjugated polymers with the reactive end-groups required for block copolymer synthesis is more challenging, hindering the development of block copolymers-containing conjugated units. Rod-coil block copolymers can be synthesized by using end-functionalized conjugated units to either grow the coil polymer using living methods, or graft to an orthogonally functionalized coil polymer. To date, there have been numerous examples of rod-coil block copolymers in the literature; however, these systems have failed to attain the range of self-assembled nanostructures seen with typical coil-coil block copolymers. This is because, in most cases, 430the self-assembly within these systems is driven largely by the stiffness and π-π interactions within the conjugated unit. For these reasons, the synthesis of rod-rod or all-conjugated block copolymers has been pursued. Although the synthesis of such systems has many challenges, several successful approaches have been developed, facilitating the preparation of numerous examples in recent years. The following sections aim to highlight some of these key examples, and focus on the significant progress made in the field to date. For a different perspective, readers are encouraged to refer to the following literature (Lee and Gomez, 2015; Robb et al., 2013).
