Alkyl substituents appended to the π-conjugated main chain account for the solution-processability and film-forming properties of most π-conjugated polymers for organic electronic device applications, including field-effect transistors (FETs) and bulk-heterojunction (BHJ) solar cells. Beyond film-forming properties, recent work has emphasized the determining role that side-chain substituents play on polymer self-assembly and thin-film nanostructural order, and, in turn, on device performance. However, the factors that determine polymer crystallite orientation in thin-films, implying preferential backbone orientation relative to the device substrate, are a matter of some debate, and these structural changes remain difficult to anticipate. In this report, we show how systematic changes in the side-chain pattern of poly(benzo[1,2-b:4,5-b']dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymers can (i) influence the propensity of the polymer to order in the π-stacking direction, and (ii) direct the preferential orientation of the polymer crystallites in thin films (e.g., "face-on" vs "edge-on"). Oriented crystallites, specifically crystallites that are well-ordered in the π-stacking direction, are believed to be a key contributor to improved thin-film device performance in both FETs and BHJ solar cells.
Tuning the chain-end functionality of a short-chain cationic homopolymer, owing to the nature of the initiator used in the atom transfer radical polymerization (ATRP) polymerization step, can be used to mediate the formation of a gel of this poly(electrolyte) in water. While a neutral end group gives a solution of low viscosity, a highly homogeneous gel is obtained with a phosphonate anionic moiety, as characterized by rheometry and diffusion nuclear magnetic resonance (NMR). This novel type of supramolecular control over poly(electrolytic) gel formation could find potential use in a variety of applications in the field of electro-active materials.
Most sustainable energy sources (solar, hydropowered, geopowered, windpowered) rely on the production of electrical energy. In the last decade, Lithium ion based batteries have emerged as interesting candidates as high-density energy storage devices, enabling the developments of electrical vehicles of constantly growing autonomies. The synthesis of polymer electrolytes and the study of their electrochemical properties is currently a very active topic. Poly(ionic liquids) (PILs), in particular, constitute an increasingly sought-after category of materials, as they are expected to replace flammable, leakage-prone organic solvent electrolytes in future energy storage devices.[1,2] In this communication, we will present a novel synthetic methodology, which provides an easy access to a broad range of PILs from a common monomeric precursor (figure 1). Owing to this straightforward conceptual approach, it is possible to precisely control the structure of the polymeric materials. We will show how the introduction of an anionic functional group on the ATRP initiator is enough to mediate gel formation at low concentrations through electrostatic interactions (Figure 2).[3,4] We will then demonstrate that the incorporation of different additives along the polymer backbone helps optimizing ionogel properties in different electrolytic solvents to form gel electrolyte. Finally, we will illustrate the potential of the resulting gels as quasi-solid materials for energy storage applications through the study of different parameters: its rheological behaviour, electrochemical stability, diffusion and ionic conductivity properties. [1] Yoshizawa, M.; Ogihara, W.; Ohno, H. Polym. Adv. Technol. 2002, 13, 589-594. [2] Wang, P.; Zakeeruddin, S. M.; Moser, J. E.; Nazeeruddin, M. K.; Sekiguchi, T.; Gratzel, M. Nat Mater 2003, 2, 402-407. [3] Appukuttan, V. K.; Dupont, A.; Denis-Quanquin, S.; Andraud, C.; Monnereau, C. Polym. Chem. 2012, 3, 2723-2726. [4] Srour, H.; Ratel, O.; Leocmach, M.; Adams, E. A.; Denis-Quanquin, S.; Appukuttan, V.; Taberlet, N.; Manneville, S.; Majesté, J.-C.; Carrot, C.; Andraud, C.; Monnereau, C. Macromol. Rapid Commun. 2014, DOI: 10.1002/marc.201400478. Figure 1
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