A SNAr-Active External Initiator that Enables Heterobifunctional Clickable Polythiophenes

Abstract

Poly(3-hexylthiophene) (P3HT) is a well-studied conjugated polymer; however, the end-group functionalization of these polymers is limited by fundamental synthetic challenges. Generally, end-capping agents are used to terminate the Kumada catalyst transfer polycondensation (KCTP) to install functional end-groups at the propagating chain end. In this work, it is shown that P3HT can be prepared with a novel SNAr-active external initiator, followed by end capping to afford heterobifunctional end-groups that exhibit orthogonal chemical reactivity. This orthogonal chemistry can be leveraged in sequential “click”-type reactions to ultimately achieve the synthesis of triblock copolymers. More specifically, it is shown that the synthesis of a new pentafluorophenyl initiator allows one to append this readily functionalized group at the initiating end during P3HT synthesis. After reaching the desired degree of polymerization, an ethynyl group is incorporated at the polymer terminus using an end-capping Grignard reagent. Critically, this heterobifunctional P3HT allows for both orthogonal para-fluoro thiol reactions, a subset of nucleophilic aromatic substitution (SNAr), and copper-catalyzed alkyne-azide cycloadditions (CuAAC). The efficacy of this heterobifunctional polymer design is demonstrated by assessing sequential “click” reactions with different nonconjugated polymer blocks to either end of the P3HT polymer block.