Synthesis of conjugated - Acidic block copolymers by atom transfer radical polymerization

Abstract

A novel series of well-defined amphiphilic triblock copolymers containing conjugated polyfluorene (PF) and coillike poly(methacrylic acid) (PMAA) were successfully synthesized by vacuum thermolysis of the precursor block copolymers, poly(2-tetrahydropyranyl methacrylate)-PF-poly-(2-tetrahydropyranyl methacrylate) (PTHPMA-PF-PTHPMA) prepared by using atom transfer radical polymerization (ATRP) with a 2-bromoisobutyrate end-capped PF as the macroinitiator. Both the linear first-order kinetic plot and the linear dependence of the Mn vs conversion indicate the controlled nature of the polymerization of THPMA. The polydispersity indices of the PTHPMA-PF-PTHPMA triblock copolymers were essentially less than 1.3, demonstrating the well-defined structures of the obtained block copolymers. The chemical structures of the PTHPMA-PF-PTHPMA block copolymers were confirmed by 1H NMR, 13C NMR, and FTIR studies. Decomposition of the precursors at about 145 °C afforded the PMAA-PF-PMAA block copolymers, and the anhydride formed during the thermolysis could be successfully transformed to the corresponding acid by further hydrolysis in warm water. PMAA-PF-PMAA and PTHPMA-PF-PTHPMA presented almost identical photophysical behavior in diluted solutions, suggesting that similar excited species were essentially involved in their luminescent processes. Aggregation of PF segments was found to occur in the aqueous solution of the PMAA-PF-PMAA as revealed by spectroscopic studies. 1H NMR results also substantiate the formation of PF aggregates stabilized by soluble PMAA.