Facile synthesis for well-defined A2B miktoarm star copolymer of poly(3-hexylthiophene) and poly(methyl methacrylate) by the combination of anionic polymerization and click reaction

摘要

We have introduced a facile synthetic route for well-defined A_2B miktoarm star copolymer composed of regioregular poly(3-hexylthiophene) and poly(methyl methacrylate) ((P3HT)_2PMMA) by the combination of anionic polymerization and click reaction. First, we synthesized PMMA terminated with 1,3,5-tris(bromomethyl)benzene (PMMA-(Br)_2) by anionic polymerization, and two bromines attached to the end of the PMMA chains were replaced by azides (PMMA-(N_3)_2). Also, monoethynyl-capped P3HT was synthesized by Grignard metathesis polymerization and post-end functionalization. Then, copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition click reaction between monoethynyl-capped P3HT and PMMA-(N_3) _2 was performed to synthesize (P3HT)_2PMMA. We used a slightly excess amount of monoethynyl-capped P3HT so that all of the azide groups at the end of the PMMA chains completely reacted with monoethynyl-capped P3HT. After complete removal of unreacted monoethynyl-capped P3HT by column chromatography, pure (P3HT)_2PMMA with narrow molecular weight distribution (the polydispersity of 1.18) was obtained. The weight fraction of P3HT and the total molecular weight of (P3HT)_2PMMA are 0.48 and 16,000, respectively. To investigate the effect of the chain architecture on optical property and thin-film morphology, we synthesized two linear P3HT-b-PMMAs (P3HT-b-PMMA-L and P3HT-b-PMMA-H) with similar weight fraction of P3HT block (0.48 for P3HT-b-PMMA-L and 0.45 for P3HT-b-PMMA-H) but two different total molecular weights (7900 for P3HT-b-PMMA-L and 15,300 for P3HT-b-PMMA-H). UV-visible (UV-vis) absorption spectrum and the fibril width of (P3HT)_2PMMA thin film were similar to those of P3HT-b-PMMA-L thin film. However, UV-vis spectrum for P3HT-b-PMMA-H thin film was red-shifted and the fibril width of P3HT-b-PMMA-H was much larger than that of (P3HT)_2PMMA. This indicates that the π-π interaction between P3HT arms in (P3HT) _2PMMA is strong enough to arrange two P3HT backbone chains in (P3HT)2PMMA to stack one by one along the nanofibril axis.