Highly Charged Conjugated Polymers with Polyphenylene Backbones and Poly(acrylic acid) Side Chains

A synthetic strategy to prepare various amphiphilic, conjugated graft copolymers by means of the grafting onto technique via click coupling reaction is described. In particular, amphiphilic, conjugated polyelectrolyte brush copolymers based on 2,7-linked carbazole fluorene copolymers as main chains and pH-sensitive, highly charged poly(acrylic acid) side chains (PAA) are presented. The main chain is obtained by a Suzuki polycondensation of dibromo- and diboronic ester of fluorene and carbazole monomers, resulting in conjugated polyphenylene-type copolymers with both alternating and statistical carbazole-fluorene structures. In order to vary the amphiphilicity of the graft copolymers, 9,9-disubstituted fluorene derivatives with different polarities, induced by branched alkyl as well as by methoxytetra(ethylene glycol) (TEG) groups, were used. To graft the side chains on the conjugated backbone, the carbazole units are, first, N-functionalized by pentynyl groups. These units are reacted in a click reaction with an azide end-functionalized poly(tert-butyl acrylate) which has previously been obtained by atom transfer radical polymerization (ATRP). After cleavage of the tert-butyl groups, the neutral comb-type copolymers were converted into a conjugated polyelectrolyte brush copolymer carrying poly(acrylic acid) side chains. The described synthetic strategy facilitates to adjust the polarity and the grafting density of the graft copolymers and might be applied to other functional side chains.