Synthesis and properties of a P3HT-based ABA triblock copolymer containing a perfluoropolyether central segment

Abstract

A poly(3-hexylthiophene)-block-perfluoropolyether-block-poly(3-hexylthiophene) (P3HT-b-PFPE-b-P3HT) triblock copolymer was synthesized by copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) in 95% yield. The copolymer was unequivocally characterized by size exclusion chromatography reaching 27 000 g mol(-1) and nuclear magnetic resonance (NMR). As expected, diffusion-ordered spectroscopy NMR experiment revealed a lower diffusion coefficient (2.56 x 10(-10) m(2) s(-1)) for the P3HT-b-PFPE-b-P3HT triblock copolymer than the ethynyl end-functionalized P3HT (2.83 x 10(-10) m(2) s(-1)). Such a triblock copolymer exhibits i) a good thermal stability with no significant weight loss until 320 degrees C under air, ii) a glass transition of -50 degrees C due to the soft PFPE segment and iii) a melting peak arising from P3HT at 236 degrees C. The UV-vis absorption spectrum exhibits a similar absorption profile to that of pure P3HT with a vibronic structure. Analysis of terpolymer thin films by atomic force microscopy imaging and grazing incidence wide-angle X-ray scattering reveals the formation of P3HT crystallites and an "edge-on" orientation of the polymer chains towards the substrate. Preliminary photovoltaic studies on blends of this triblock copolymer combined with a fullerene derivative indicate that the devices using P3HT-b-PFPE-b-P3HT show an almost similar power conversion efficiency to commercial P3HT.