Semiconducting donor-acceptor (D-A) polymers have attracted considerable attention towards the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications.Here, polydiketopyrrolopyrrole (PDPP)-based D-A polymers with varied alkyl side-chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (T g ) with increasing side-chain length, which is further verified through coarse-grained molecular dynamics (CG-MD) simulations. Informed from experimental results, a mass-per-flexible bond model is developed to capture such observation through a linear This article is protected by copyright. All rights reserved. 3 correlation between T g and polymer chain flexibility. Using this model, a wide range of backbone T g over 80 C and elastic modulus over 400 MPa can be predicted for PDPP-based polymers. This study highlights the important role of side-chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict T g and modulus of future new D-A polymers.) The synthesis part was financially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Discovery Grant (RGPIN-2017-06611), and by the Canadian Foundation for Innovation (CFI). M. U. O. thanks NSERC for a doctoral scholarship.

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 new approach for improving the mechanical properties of semiconducting polymers was established via physical combination of a diketopyrrolopyrrole-based conjugated polymer with a low-molecularweight branched polyethylene (BPE). The influence of the BPE additive on the stretchability and mechanical properties of the conjugated polymer was studied at different scales, using various characterization techniques, including atomic force microscopy, UV−vis spectroscopy, and grazing incidence X-ray diffraction. At the micron scale, the BPE additive acts as a plasticizer and significantly reduces Young's modulus of the conjugated polymer and increases the crack onset strain, reaching a maximum of a 75% strain elongation when 90 wt % of BPE is blended with the conjugated polymer. The introduction of BPE to the blended systems decreases the crack propagation of polymer thin films, making them softer and more ductile, with Young's modulus of 112 MPa at 25 wt % of BPE before thermal annealing. At the nanoscale, the improvement of stretchability is shown by the reduction of the crack size under a 100% strain, going from 3100 to 600 nm at 0 and 90 wt % of BPE, respectively. The results obtained in this investigation confirm that an improvement in the mechanical properties and a modulation of the solid-state morphology of the semiconducting materials can be enabled by the physical mixing of conjugated polymers with a nontoxic, low-molecular-weight branched polyethylene, particularly favorable for the solution deposition of organic semiconductors.

A side-chain engineering study has been performed with isoindigo-based conjugated polymers to modulate their physical and electronic properties through the incorporation of urea-containing and saturated linear side chains.