Crystallization-driven self-assembly of poly(3-hexylthiophene)-b-poly(2,5-bis(2-ethylhexyloxy)p-phenylene), a π-conjugated diblock copolymer with a rigid rod corona-forming block

Abstract

Crystallization-driven self-assembly (CDSA) of polymeric amphiphiles with a crystallizable core-forming block has emerged as a powerful method to create morphologically pure samples of 1-dimensional (1D) nanofibers with a wide array of potential applications. Many previous investigations into solution phase π-conjugated block copolymer (BCP) CDSA have focussed on BCPs with a crystalline rod-like core-forming block and amorphous, coil-like corona-forming block. Reports on the solution-phase CDSA of BCPs where both the core- and corona-forming blocks are rigid are comparatively rare. Here we report studies of the synthesis and self-assembly of two all-conjugated poly(3-hexylthiophene)-b-poly(2,5-bis(2-ethylhexyloxy)p-phenylene) BCPs (P3HT₆₀-b-PPP₃₀ and P3HT₃₅-b-PPP₁₅) with crystallizable P3HT core-forming blocks and different overall molar masses but similar core : corona block ratios (∼2 : 1). Previous self-assembly studies using similar materials only produced short nanofibers (∼120 nm) while we were able to fabricate long (>5 μm) polydisperse nanofibers from both materials here, which are desirable for optoelectronic applications. WAXS and AFM were used to characterize the internal nanofiber core crystallinity and the nanoscale morphology, respectively, and UV/Visible spectroscopy was used to probe the temperature-dependent crystallization behaviour, including at temperatures where self-nucleation was supressed upon cooling (≥50 °C). This work provides a method for forming long polydisperse nanofibers with well-connected core domains for potential applications involving energy transfer.