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 UV-vis 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 co-micelles through the growth of P3HT70-b-PS197 from the termini of rrP3HT106-b-rsP3HT47 nanofibers that function as seed micelles, and also multi-arm star-like arrays of fiber-like micelles with variable arm-lengths, which were formed when seed micelles derived from rrP3HT150 homopolymer were used.