Fiber-like Micelles viathe Crystallization-DrivenSolution Self-Assembly of Poly(3-hexylthiophene)-block-Poly(methyl methacrylate) Copolymers.

The solution self-assembly of block copolymers with aπ-conjugated,crystalline, core-forming block represents a facile strategy towardthe preparation of semiconducting nanowires with potential for high-techapplications. In this study, two asymmetric block copolymers basedon regioregular poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate)(PMMA), namely P3HT40-b-PMMA520(6a) and P3HT40-b-PMMA1100(6b) (block ratios = 1:13 and 1:27.5, respectively)were prepared via atom transfer radical polymerization (ATRP) froma P3HT macroinitiator. The solution self-assembly of the P3HT-b-PMMA block copolymers was subsequently studied under avariety of experimental conditions. Short, fiber-like micelles resultedwhen THF (common solvent for P3HT and PMMA) solutions of the blockcopolymer were dialyzed against ethyl acetate and n-butyl acetate (selective solvents for PMMA). The electronic propertiesof the fiber-like micelles obtained coupled with wide-angle X-rayscattering studies confirmed that the cores of the aggregates werecrystalline and suggested that growth occurs via a crystallization-drivenpathway. The average lengths of fiber-like micelles were shown toincrease relative to those obtained from dialysis versus the PMMAselective solvent, when THF was slowly evaporated from mixtures containing n-butyl acetate and P3HT-b-PMMA unimers,thereby limiting the rate of P3HT aggregation. Furthermore, the formationof only relatively short (mainly under 200 nm, always <1 μm)fiber-like micelles in these studies, even when the ratio of THF/alkylacetate was controlled carefully via dialysis or evaporation, indicatedthat homogeneous nucleation of P3HT-b-PMMA blockcopolymers is relatively facile. This behavior differs significantlyfrom that detected for other block copolymers such as polyferrocenylsilane-basedmaterials that undergo crystallization-driven self-assembly to formcylinders with lengths of up to 10 μm under analogous conditions. [ABSTRACT FROM AUTHOR]