Efficient and Controlled Seeded Growth of Poly(3-hexylthiophene) Block Copolymer Nanofibers through Suppression of Homogeneous Nucleation

Low-dispersity, length-tunable block copolymer nanofibers with spatially controlled functionalization and a crystalline core have recently become accessible using the ambient temperature, living crystallization-driven self-assembly (CDSA) seeded-growth method. The crystallizable π-conjugated polymer, poly(3-hexylthiophene) (P3HT), is of particular interest as a core-forming block as a result of its useful optoelectronic properties. However, attempts to apply the living CDSA method to P3HT diblock copolymers have had limited success as, in addition to seeded growth, homogeneous nucleation events result in the spontaneous formation of new fibers, which leads to a loss of length control. Herein, we demonstrate that by performing detailed variable temperature ultraviolet–visible (UV–vis) spectroscopic studies of the homogeneous nucleation of rrP3HT₁₀₆-b-rsP3HT₄₇ block copolymer (rr = regioregular and rs = regiosymmetric, respectively) we were able to identify conditions (40 °C) under which spontaneous (homogeneous) nucleation is suppressed. Addition of preformed seeds under these conditions allowed for highly efficient living CDSA to yield nanofibers with a rrP3HT₁₀₆ core and controllable lengths up to ca. 4 μm with low length dispersity. Analogous use of this technique also allowed the efficient preparation of B-A-B triblock comicelles through the growth of P3HT₇₀-b-PS₁₉₇ from the termini of rrP3HT₁₀₆-b-rsP3HT₄₇ nanofibers that function as seed micelles, and also multiarm starlike arrays of fiberlike micelles with variable arm lengths, which were formed when seed micelles derived from rrP3HT₁₅₀ homopolymer were used.