Copolymers of pyrrole with N-alkynylpyrroles

Electrochemical oxidative copolymerization was carried out between pyrrole and N-substituted pyrroles, Pr(CCPh) (Ph = phenyl) and Pr(CCSiEt3), which have CCPh and CCSiEt3 groups, respectively, at the N-position of pyrrole. The electrochemical oxidation of Pr(CCPh) and Pr(CCSiEt3) required potentials about 0.5–0.8 V higher than that of pyrrole because of the presence of the electron-pulling acetylenic group, and the electrochemical copolymerization gave copolymers with pyrrole-rich compositions. Copolymers of pyrrole with Pr(CCPh) showed an electrical conductivity of 2–6.3 S cm−1. These copolymers showed thermal stability: 50–85 °C higher than the homopolymer of pyrrole. A dimeric compound of Pr(CCPh), i.e., (PrCCPh)2, was prepared, and its X-ray crystallographic analysis essentially revealed a pyrrole–pyrrole coplanar structure; this supports the notion that the CCPh group attached at the N-position of pyrrole does not break π-conjugation in the polypyrrole main chain of the copolymer.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electrochemical copolymerization of pyrrole with N-alkynylpyrroles. ► The copolymers showed considerably higher thermal stability than polypyrrole. ► Synthesis of N-alkynylpyrroles and a dimer. ► X-ray molecular structures of the N-alkynylpyrroles and dimer. ► Optical and electrochemical data of the N-alkynylpyrroles and dimer.