Regioregularity-Driven Morphological Transition of Poly(3-hexylthiophene)-Based Block Copolymers

Abstract

Conjugated polymer-based block copolymers (BCPs) offer great potential to provide beneficial nanostructures for efficient organic optoelectronics. However, their complicated self-assembly behavior, which is attributed to the strong crystallization of conjugated blocks, is still not well understood due to the lack of a model BCP system. Herein, we develop a series of novel conjugated polymer-based BCPs, poly­(3-hexyl­thiophene)-block-poly­(2-vinylpyridine) (P3HT-b-P2VP), in which the regioregularity (RR) of the P3HT block was varied from 95 to 73%. The tunable RR content allows for precise regulation of P3HT crystallization with minimal influence on the microphase-separation force between the P3HT and P2VP blocks. When RR is high (i.e., 95 or 85%), structure formation is controlled by crystallization of P3HT, and the ultimate structure is characterized by nanoscale P3HT fibrils in an amorphous matrix. In contrast, as RR decreases to 78 and 73%, P3HT crystallization is suppressed. The self-assembly is controlled by the enthalpic interaction between P3HT and P2VP blocks, much like typical BCPs having two flexible blocks, and thermal annealing drives the formation of well-ordered lamellar or cylindrical phases. This morphological behavior is consistent with a Monte Carlo simulation based on a newly developed coarse-grained model. Significantly, this novel class of RR-controlled P3HT-based BCPs provides a simple method to tune bulk and thin film morphology for a variety of applications in nanostructured organic electronics.

Regioregularity-control of conjugated polymers: from synthesis and properties, to photovoltaic device applications

“…Lowering the RR allows the formation of ordered nanostructures by weakening the initially strong molecular interactions in the P3HT blocks and, thus, enthalpic interaction can govern the phase behaviors of the block copolymers. [87][88][89] These different self-assembled structures formed by rre and rra P3ATs result in signicant differences in their optoelectrical properties (Fig. 4c).…”

Synthesis and Self-Assembly of Conjugated Block Copolymers

“…High RR P3HT- b -P2VP has a very strong interchain interaction and is preferential to crystalline, which makes it difficult to form an ordered nanostructure. In contrast, crystallization is inhibited in low RR P3HT- b -P2VP and well-ordered nanostructures are achieved, i.e., lamellar and cylindrical phases [ 120 ]. They also found that the domain space of poly(3-dodecylthiophene)- b -poly(2-vinylpyridine) (P3DDT- b -P2VP) can be tuned by regulating the RR of the P3DDT block ( Figure 14 ) [ 121 ].…”

Random Copolymers Allow Control of Crystallization and Microphase Separation in Fully Conjugated Block Copolymers

“…In contrast, when the segregation strength is low, crystallization breaks out of the microphase-separated domains and dominates the morphology of the block copolymer. 46 This concept has also been demonstrated in rod−coil block copolymers containing one semiflexible, semicrystalline block and one flexible, amorphous block, including poly(3-hexylthiophene-2,5-diyl)-block-poly(2-vinylpyridine), 47,48 poly(3-dodecylthiophene-2,5-diyl)-block-poly(methyl methacrylate), 49 poly(3-hexylthiophene-2,5-diyl)-block-poly(perylene bisimide acrylate), 50,51 and poly(3-(2′-ethyl)hexylthiophene)-block-polylactide. 52 In these rod−coil block copolymers, various microphase-separated morphologies, including spheres, cylinders, and lamellae, are observed only when the composition of the block copolymer is dominated by the flexible block.…”