Amphiphilic poly(alkylthiophene) block copolymers prepared via externally initiated GRIM and click coupling

Abstract

Block copolymers with a poly(3-alkylthiophene) (P3AT) polymer block can self-organize into periodic, crystalline nanostructures that may be useful for organic electronic applications. However, reliable synthetic methods for the preparation of P3AT block copolymers are lacking. Here, we demonstrate a general method for the synthesis of P3AT rod-coil block copolymers via click-coupling of alkynyl-P3AT. Alkynyl-P3ATs are prepared via externally initiated Grignard metathesis polymerization (GRIM) using a modified nickel catalyst followed by end-group modification. The resulting alkynyl-P3ATs have improved stability and solubility compared with those previously reported. P3ATs are subsequently coupled to an azide-functionalized poly(ethylene glycol) through copper-catalyzed azide–alkyne click coupling, resulting in P3AT-b-PEG block copolymers. The advantages of this synthetic procedure are the improved stability of the alkynyl-P3AT macroreagent, the capability to synthesize high molecular weight P3AT polymer blocks, and facile determination of P3AT absolute molecular weight through 1H NMR analysis. This synthetic method is applied to prepare a series of P3AT-b-PEG block copolymers, with poly(3-hexyl thiophene) (P3HT), poly(3-dodecylthiophene) (P3DDT), and poly(3-(2′-ethyl)hexylthiophene) (P3EHT) polymer blocks. The resulting P3AT block copolymers are dispersed in water to form micelles with crystalline, hydrophobic cores. Absorbance measurements show that crystallization of P3DDT and P3EHT blocks is suppressed in micellar cores due to nanoscale confinement of the P3AT blocks.