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1. Tuning the surface energies in a family of poly-3-alkylthiophenes bearing hydrophilic side-chains synthesized via direct arylation polymerization (DArP)

   https://doi.org/10.1039/D1PY00195G  

   Schmitt, Alexander ; Samal, Sanket ; Thompson, Barry C. ( May 2021 , Polymer Chemistry)

   null (Ed.)

   Recent work has identified surface energy as a key figure of merit in predicting the morphology of bulk heterojunction organic solar cells and organic alloy formation in ternary blend organic solar cells. An efficient way of tuning surface energy in conjugated polymers is by introducing functionalised side chains. Here, we present a systematic study on a family of poly(3-hexylthiophene) (P3HT)-based random copolymers bearing five different functionalised side chains (ester, ether, diether, carbamate, nitrile) prepared by direct arylation polymerization (DArP) in terms of their effectiveness in tuning surface energy. This study also exemplifies the superior functional group tolerance in DArP compared to more traditional polymerization procedures. Water droplet contact angle measurements revealed that especially carbamates are highly effective in tuning surface energy, increasing the surface energy from 21.2 mN m −1 with P3HT to 25.5 mN m −1 and 28.6 mN m −1 in 25% and 50% carbamate functionalized copolymers, respectively. Importantly, by introducing a two-carbon-spacer between the conjugated backbone and the functional group, optical and electronic properties of P3HT could be largely maintained in the copolymers as determined by UV/Vis, cyclic voltammetry and space charge limited current hole mobility. 

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2. Enabling Conducting Polymer Applications: Methods for Achieving High Molecular Weight in Chemical Oxidative Polymerization in Alkyl- and Ether-Substituted Thiophenes

   https://doi.org/10.3390/ma14206146  

   Hebert, David D. ; Naley, Michael A. ; Cunningham, Carter C. ; Sharp, David J. ; Murphy, Emma E. ; Stanton, Venus ; Irvin, Jennifer A. ( October 2021 , Materials)

   Polythiophenes (PTs) constitute a diverse array of promising materials for conducting polymer applications. However, many of the synthetic methods to produce PTs have been optimized only for the prototypical alkyl-substituted example poly(3-hexylthiophene) (P3HT). Improvement of these methods beyond P3HT is key to enabling the widespread application of PTs. In this work, P3HT and two ether-substituted PTs poly(2-dodecyl-2H,3H-thieno[3,4-b][1,4]dioxine) (PEDOT-C12) and poly(3,4-bis(hexyloxy)thiophene) (PBHOT) are synthesized by the FeCl3-initiated oxidative method under different conditions. Polymerization was carried out according to a common literature procedure (“reverse addition”) and a modified method (“standard addition”), which differ by the solvent system and the order of addition of reagents to the reaction mixture. Gel-permeation chromatography (GPC) was performed to determine the impact of the different methods on the molecular weights (Mw) and degree of polymerization (Xw) of the polymers relative to polystyrene standards. The standard addition method produced ether-substituted PTs with higher Mw and Xw than those produced using the reverse addition method for sterically unhindered monomers. For P3HT, the highest Mw and Xw were obtained using the reverse addition method. The results show the oxidation potential of the monomer and solution has the greatest impact on the yield and Xw obtained and should be carefully considered when optimizing the reaction conditions for different monomers. 

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3. Enhanced and unconventional responses in chemiresistive sensing devices for nitrogen dioxide and ammonia from carboxylated alkylthiophene polymers

   https://doi.org/10.1039/D0MH00049C  

   Wagner, Justine ; Jang, Hyun-June ; Han, Jinfeng ; Katz, Howard E. ( May 2020 , Materials Horizons)

   A carboxylated thiophene polymer-based chemiresistive device in a field-effect transistor (FET) configuration with unusual and enhanced responses to the widespread pollutants nitrogen dioxide (NO 2 ) and ammonia (NH 3 ) is described. The device based on a polymeric thiophene carboxylic acid showed a dramatic and superlinear increase in drain current ( I D ) of over 15 000% to a ramped exposure to 10 ppm NO 2 over several minutes, while its ethyl ester counterpart had significantly lower response. Devices incorporating either an ester or carboxylic acid displayed comparable and previously unreported increases in I D from 10 ppm ramped NH 3 exposure of 200–300%. Conventional poly(alkylthiophenes) showed the expected current decreases from similar NH 3 exposures. Using threshold voltage shifts in silicon transistors coupled to our recently reported remote gate (RG) platform with thiophene polymer coatings, we determined that two differing response mechanisms are associated with the two gas exposures. By calculating the charge density induced in the polymers by NO 2 exposure using the silicon transistor voltage shifts, we conclude that proton conduction contributes significantly to the high sensitivity of the carboxylic acid to NO 2 , in addition to doping that was observed for all four polymers. Furthermore, hydrogen bonding moieties of the carboxylic acid and ester may be able to physisorb NH 3 and thus alter the charge distribution, rearrange polymer chains, and/or create a proton transfer network leading to the I D increase that is the opposite of the response obtained from non-carboxylated thiophene polymers. 

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4. An experimental and computational study of donor–linker–acceptor block copolymers for organic photovoltaics

   https://doi.org/10.1002/polb.24633  

   Hu, Zhiqi ; Jakowski, Jacek ; Zheng, Chenyu ; Collison, Christopher J. ; Strzalka, Joseph ; Sumpter, Bobby G. ; Verduzco, Rafael ( August 2018 , Journal of Polymer Science Part B: Polymer Physics)

   Block copolymers with donor and acceptor conjugated polymer blocks provide an approach to dictating the donor–accepter interfacial structure and understanding its relationship to charge separation and photovoltaic performance. We report the preparation of a series of donor‐linker‐acceptor block copolymers with poly(3‐hexylthiophene) (P3HT) donor blocks, poly((9,9‐dioctylfluorene)‐2,7‐diyl‐alt‐[4,7‐bis(thiophen‐5‐yl)‐2,1,3‐benzothiadiazole]‐2′,2″‐diyl) (PFTBT) acceptor blocks, and varying lengths of oligo‐ethylene glycol (OEG) chains as the linkers. Morphological analysis shows that the linkers increase polymer crystallinity while a combination of optical and photovoltaic measurements shows that the insertion of a flexible spacer reduces fluorescence quenching and photovoltaic efficiencies of solution processed photovoltaic devices. Density functional theory (DFT) simulations indicate that the linking groups reduce both charge separation and recombination rates, and block copolymers with flexible linkers will likely rotate to assume a nonplanar orientation, resulting in a significant loss of overlap at the donor–linker–acceptor interface. This work provides a systematic study of the role of linker length on the photovoltaic performance of donor–linker–acceptor block copolymers and indicates that linkers should be designed to control both the electronic properties and relative orientations of conjugated polymers at the interface. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2018,56, 1135–1143

    

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5. Self-immolative polymers with potent and selective antibacterial activity by hydrophilic side chain grafting

   https://doi.org/10.1039/C8TB01632A  

   Ergene, Cansu ; Palermo, Edmund F. ( January 2018 , Journal of Materials Chemistry B)

   We report the first example of a self-immolative polymer that exerts potent antibacterial activity combined with relatively low hemolytic toxicity. In particular, self-immolative poly(benzyl ether)s bearing pendant cationic ammonium groups and grafted poly(ethylene glycol) chains in their side chains were prepared via post-polymerization thiol–ene chemistry. These functional polymers undergo sensitive and specific triggered depolymerization into small molecules upon exposure to a designed stimulus (in this example, fluoride ions cleave a silyl ether end cap). The molar composition of the resulting statistical copolymers varied from 0 to 100% PEG side chains. The average molar mass of the pendant PEG chains was either 800 or 2000 g mol −1 . The antibacterial and hemolytic activities were evaluated as a function of copolymer composition. Strong bactericidal activity (low μg mL −1 MBC) was retained in the copolymers containing 25–50% PEG-800, whereas hemolytic toxicity monotonically decreased (up to HC 50 >1000 μg mL −1 ) with increasing PEG content. PEG-2000 was far less effective; both the MBC and HC 50 decreased to a comparable extent with increasing PEGylation. Overall, the best cell type selectivity index (HC 50 /MBC ∼ 28) was obtained for the copolymer containing ∼50% cysteamine and ∼50% PEG-800 side chains, as compared to the cationic homopolymer (HC 50 /MBC < 1). Thus, the systematic tuning of the PEG graft density and chain length effectively enhances the cell-type selectivity of these self-immolative polymers by orders of magnitude. 

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