A simple and efficient strategy to modulate the self-assembly and solid-state morphology of conjugated polymers has been developed by incorporating various amounts of amide-containing alkyl side chains to high charge carrier mobility conjugated polymers based on diketopyrrolopyrrole (DPP). Synthetically easily accessible and tunable, the incorporation of amide-containing side chains is a direct strategy to promote intermolecular hydrogen bonding between polymer chains and tune the solid-state morphology. Incorporation of 5–30 mol % of amides in the conjugated polymers was performed without a drastic decrease of solubility. The incorporation of hydrogen-bonding moieties allowed for an improvement of the charge carrier mobility in organic field-effect transistors (OFET) devices, which achieved a maximum value of 2.46 cm2/(V s) at 5 mol % of amides. Morphological investigation showed that the intermolecular hydrogen bonds formed between adjacent amide moieties directly affected the lamellar packing of the polymer and aggregation, without affecting the π-conjugation. Therefore, controlled self-assembly of conjugated polymers through hydrogen-bonding side chains is a promising strategy toward more efficient semiconducting polymers for thin film transistors and other organic electronics.
An efficient strategy to modify the mechanical properties of conjugated polymers has been developed through the incorporation of amide moieties.
A new strategy for influencing the solid-state morphology of conjugated polymers was developed through physical blending with a low-molecular-weight branched polyethylene. This nontoxic and low-boiling-point additive was blended with a high-charge-mobility diketopyrrolopyrrole-based conjugated polymer, and a detailed investigation of the new blended materials was performed by various characterization tools, including X-ray diffraction, UV–vis spectroscopy, and atomic force microscopy. Interestingly, the branched additive was shown to reduce the crystallinity of the conjugated polymer while promoting aggregation and phase separation in the solid state. Upon thermal removal of the olefinic additive, the thin films maintained a lower crystallinity and aggregated morphology in comparison to a nonblended polymer. The semiconducting performance of the new branched polyethylene/conjugated polymer blends was also investigated in organic field-effect transistors, which showed a stable charge mobility of around 0.3 cm2 V–1 s–1 without thermal annealing, independent of the blending ratio. Furthermore, using the new polyethylene-based additive, the concentration of a conjugated polymer required for the fabrication of organic field-effect transistor devices was reduced down to 0.05 wt %, without affecting charge transport, which represents a significant improvement compared to usual concentrations used for solution deposition. Our results demonstrate that the physical blending of a conjugated polymer with nontoxic, low-molecular-weight branched polyethylene is a promising strategy for the modification and fine-tuning of the solid-state morphology of conjugated polymers without sacrificing their charge-transport properties, thus creating new opportunities for the large-scale processing of organic semiconductors.
A huge challenge for developing self-healing materials is achieving a good compromisation between mechanical properties and self-healing efficiency. For this purpose, a facile route by introducing N-(hydroxymethyl)acrylamide (NMA) as a thermal-catalyzed self-cross-linker as well as a self-healing material into a soft polymer system for tuning the mechanical properties in an easy way, resulting in elastic and self-healing properties through a covalent and dynamic network simultaneously, represents an exciting avenue for the development of self-healing materials. Specifically, we propose a simple strategy to synthesize a self-cross-linkable poly{(n-butyl acrylate)-co-[N-(hydroxymethyl)acrylamide]} (PBA x -co-PNMA y ) amphiphilic copolymer prepared by radical polymerization method, where x and y are BA and NMA ratios, respectively, based on the monomer composition in the obtained copolymer. The mechanical properties and self-healing efficiency of the copolymer can be easily tuned by controlling the monomer ratios and varying the self-cross-linking reaction conditions. PBA0.8-co-PNMA0.2 in bulk solid state possesses a stretchability of up to 191%, maximum stress of 571 kPa, and a self-healing efficiency of 90% in ambient conditions without any interventions. Owing to the hydrophobic nature of PBA in the copolymer system, self-healing can be triggered even underwater. Furthermore, a microscale thin film bestowed with identical self-healing and mechanical properties can be fabricated and the behavior of the copolymer in thin-film form was inspected using a pseudofreestanding tensile tester machine. This work provides insight into the future design of materials with elastic, self-cross-linking, and self-healing properties, which are adjustable depending on the desired applications.
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