Exploring the Graft-To Synthesis of All-Conjugated Comb Copolymers Using Azide–Alkyne Click Chemistry

Copolymers with graft architectures possess interesting material properties distinct from their linear polymer counterparts. The effects of multidimensional architectures on the optoelectronic and physical properties of all-conjugated graft copolymers are not well-known, thus providing a large incentive for their study. In order to readily access these materials (hypothesized to have “comb” architectures), it is extremely important to investigate the methods used in their synthesis. Here we study the graft-to synthesis of comb copolymers composed of polythiophene backbones and polyselenophene side chains and identify the opportunities and challenges associated with copolymer formation. Azide-functionalized polythiophene “backbones” and acetylene-terminated polyselenophene “side chains” were synthesized in a controlled fashion using Kumada catalyst-transfer polycondensation (KCTP) polymerization and grafted together using copper-catalyzed azide–alkyne click chemistry (CuAAC). ¹H NMR, GPC, and FTIR results confirm the attachment of polyselenophene side chains to the polythiophene backbone, resulting in comb copolymers with varying grafting densities. Low grafting density copolymers are readily synthesized using various backbone and side chain polymers. Midrange grafting density copolymers are more challenging but can be accessed when the availability of the graft sites on the polythiophene backbones is maximized. The synthesis of high grafting density combs remains challenging even when various modifications to the backbone and side chain polymers are implemented to improve the grafting efficiency. Problematic Glaser homocoupling of acetylene-terminated polyselenophenes was observed in certain conditions; however, this can be successfully prevented using an organic-soluble copper catalyst which is broadly applicable to many polymer–polymer CuAAC reactions. Ultimately, this investigation demonstrates a graft-to synthetic method that is useful for low- and midgrafting density all-conjugated comb copolymers, thus providing a means to further the study of these interesting multidimensional semiconducting materials.