Electronic Properties and Field‐Effect Transistors of Thiophene‐Based Donor–Acceptor Conjugated Copolymers

Summary: The thiophene‐quinoxaline donor–acceptor conjugated copolymer poly[(thiophene‐2,5‐diyl‐alt‐(2,3‐diheptylquinoxaline‐5,8‐diyl)] (PTHQx) was explored as a semiconductor in thin‐film organic field‐effect transistors (OFETs). A hole mobility of 3.6 × 10⁻³ cm² · V⁻¹ · s⁻¹ and an on/off current ratio of 6 × 10⁵ were observed in p‐channel OFETs made from spin‐coated PTHQx thin films. The electronic structures of PTHQx and a related thiophene‐thienopyrazine donor–acceptor copolymer were calculated by density functional theory. Atomic force microscopy of PTHQx thin films showed a polycrystalline grain morphology that varied with the substrate.

Output (left) and transfer (right) characteristics of a PTHQx (structure shown) organic field‐effect transistor.     

The Electrical Conductivity of Graphite Nanoplatelet Filled Conjugated Polyacrylonitrile

The electrical conductivity of composites of exfoliated graphite nanoplatelets (GNPs), including bromine‐doped GNP, and conjugated polyacrylonitrile has been investigated. The focal point is the dual nature of the graphite nanoparticles, which exhibit both intrinsic electrical conductivity and doping capability of semi‐conductive polymers such as conjugated polyacrylonitrile to form charge‐transfer complexes. The conductivity is particularly enhanced in conjugated polyacrylonitrile composites (e.g., with 6 wt.‐% graphite nanoplatelets) where the value rises from 1 × 10⁻¹⁰ to 2 × 10⁻³ S · cm⁻¹, which reflects jointly the conductivity of the doped semi‐conductive polymer together with the percolation‐based conductivity of the particles.

     

New Heteroaromatic Polymers Consisting of Alkyl‐ and Amino‐1,3,5‐triazine Units. Their Basic Optical Properties and n‐Type Time‐of‐Flight Drift Mobility

Summary: Alternating copolymers between substituted 1,3,5‐triazine (substituent = alkyl or amine) and thiophene or bithiophene are synthesized. The copolymer of amino‐1,3,5‐triazine with thiophene is soluble in organic solvents, transparent in most parts of the visible region, and photoluminescent. The copolymer receives electrochemical n‐doping with an E_pc of −2.08 V vs Ag⁺/Ag and shows a time‐of‐flight electron drift mobility of 2.0 × 10⁻⁴ cm² · V⁻¹ · s⁻¹, which is larger than that of widely used Al(8‐quinolinolato)₃.

Structure of the poly(1,3,5‐triazine)s.     

Large Deformable Multiwalled Carbon Nanotube Core–Shell Structure on Polystyrene Beads

Multiwalled carbon nanotube (MWCNT)‐coated polystyrene (PS) beads have been prepared by dispersion polymerization followed by a layer‐by‐layer self‐assembly method. The concentration of carboxylic acid groups on the MWCNTs increased from 1.81 × 10²¹ to 3.43 × 10²² COO⁻ per g as the treatment time was increased from 3 to 9 h. The sulfonated polystyrene (SPS) beads changed from being negatively charged to positively charged when the cationic polyelectrolyte was self‐assembled on their surface. The surface morphology of the adsorbed polyelectrolyte was smooth without any aggregation and the thickness of the polyelectrolyte coating on the SPS beads was ≈0.6 µm. The electrical conductivity and resistance of the MWCNT‐coated SPS beads were measured to be 4.0 × 10⁻² S · cm⁻¹ and 12.8 Ω at a volume fraction of 91%, respectively.

     

Thioketone‐Mediated Polymerization of Butyl Acrylate: Controlling Free‐Radical Polymerization via a Dormant Radical Species

It is demonstrated by experiment and simulation that the commercially available thioketone 4,4‐bis(dimethylamino)thiobenzophenone is capable of controlling AIBN‐initiated bulk butyl acrylate polymerization at 80 °C. On the basis of molecular weight data and from monomer conversion versus time curves, the associated rate parameters are estimated. The addition rate coefficient, k_ad, for the reaction of a propagating chain with the thioketone is close to 10⁶ L · mol⁻¹ · s⁻¹ and the fragmentation rate coefficient, k_frag, is around 10⁻² s⁻¹ giving rise to large equilibrium constants in the order of 10⁸ L · mol⁻¹. Furthermore, cross‐ and self‐termination of the dormant radical species are identified to be operational.

     

Synthesis and Characterization of Pyrene‐Centered Starburst Oligofluorenes

A series of starburst materials ( T1 – T3 ) based on a pyrene core with four oligofluorene arms of different length have been synthesized and characterized. The starburst materials show good film forming ability and sky blue fluorescence. Electroluminescent devices take on a stable blue emission and the device performance increases with an increase in arm length. The single‐layered device made of T3 has a maximum brightness of over 2 700 cd · m⁻² and a maximum current efficiency of 1.75 cd · A⁻¹, which is among the best in starburst material devices. The morphology of T1 – T3 has been studied by atomic force microscopy. The starburst oligofluorenes with different arm lengths show a distinctive texture, which indicates the size dependent morphology of the starburst materials.

     

Ambipolar Field‐Effect Transistor (FET) and Redox Characteristics of a π‐Conjugated Thiophene/1,3,4‐Thiadiazole CT‐Type Copolymer

Summary: A π‐conjugated charge transfer‐type copolymer consisting of an electron‐donating thiophene and an electron‐accepting 1,3,4‐thiadiazole, P(ThdzTh), underwent facile electrochemical p‐ and n‐doping, as revealed by cyclic voltammetry. The copolymer gave a new ambipolar field‐effect transistor (FET), which showed typical I_DS (source–drain current)–V_DS (source–drain voltage) curves in both a p‐type working mode and an n‐type working mode. In the n‐type working mode, the polymer showed a carrier mobility of about 5 × 10⁻³ cm² · V⁻¹ · s⁻¹ and an on/off ratio of about 3 × 10⁴.

n‐Channel field‐effect transistor characteristics of P(ThdzTh).     

A Novel Poly(aryleneethynylene) with Tetrathiafulvalene (TTF) Side Chains: Synthesis,Self‐Assembly,and Electroactive Property

A novel poly(aryleneethynylene), in which the main chain and the tetrathiafulvalene (TTF) side chains are coplanar, has been prepared and characterized. The polymer can self‐assemble in tetrahydrofuran (THF) and the π‐extended coplanar backbones adopt good face‐to‐face stacking, which is confirmed by X‐ray diffraction (XRD) analysis. Cyclic voltammetry has revealed that the polymer has reversible electroactive properties. The optical bandgap deduced by UV‐vis absorption spectroscopy and the electrochemical bandgap are 2.03 and 2.14 eV. The conductivities of the powder and the realigning solid of the polymer are 6 × 10⁻⁸ and 4 × 10⁻⁶ S cm⁻¹.

     

Controlled Radical Ab Initio Emulsion Polymerization of n‐Butyl Acrylate by Reverse Iodine Transfer Polymerization (RITP): Effect of the Hydrolytic Disproportionation of Iodine

Summary: Controlled radical polymerization of n‐butyl acrylate by reverse iodine transfer polymerization (RITP) was achieved in ab initio emulsion polymerization to yield a stable and uncolored latex (particle diameter d_p = 106 nm). Hydrolysis of iodine, I₂, was responsible for an upward deviation from the targeted molecular weight = 10 400 g · mol⁻¹. The iodide concentration [I⁻] was followed by an iodide selective electrode and the amount of efficient iodine (33%) was successfully correlated with the experimental molecular weight = 31 000 g · mol⁻¹. Finally, a simplified mechanism of RITP in ab initio emulsion polymerization taking into account the iodine hydrolysis was proposed.

Evolution of molecular weight and polydispersity index in RITP of BuA in ab initio emulsion.     

Synthesis and Evaluation of Novel Proton Exchange Membranes Containing the Semisquaric Acid Group

We focus our attention here on semisquaric acid, which is known to show high acidity, as a new proton dissociating group for proton exchange membranes (PEMs). The introduction of a squaric acid group into aromatic polymers was conducted by the reaction of lithiated aromatic polymers and diisopropoxy squarate, followed by treatment with hydrochloric acid. A resulting polyphenylsulfone membrane with the squaric acid group introduced (PPSf‐SQ, IEC = 4.1 meq·g⁻¹) showed proton conductivity of 1.0 × 10⁻¹ S·cm⁻¹ at 80 °C under 95% relative humidity, which indicates that the semisquaric acid has the potential to become an alternative proton‐conducting group for PEMs.

     

Synthesis of PEDOT Nanoparticles and Vesicles by Dispersion Polymerization in Alcoholic Media

Summary: The synthesis of PEDOT nanoparticles and vesicles by dispersion polymerization in a methanol/water mixture (3/2, v/v) is reported, using either ammonium persulfate or iron(III) p‐toluenesulfonate as oxidants and α‐EDOT‐PEO as a reactive stabilizer. The influence of the oxidant as well as the α‐EDOT‐PEO molar mass and concentration on the core‐shell particle morphology and conductivity properties have been investigated. PEDOT particles with conductivities up to 1.5 × 10⁻² S · cm⁻¹ have been obtained in high yield.

TEM image of PEDOT vesicles prepared using PEO‐based stabilizers of 25 000 g · mol⁻¹ in water/methanol mixture (2:3 v/v) at room temperature using ammonium persulfate as an oxidant.     

Synthesis of Cyclopentadienyl Capped Polyethylene and Subsequent Block Copolymer Formation Via Hetero Diels‐Alder (HDA) Chemistry

In the current contribution it is demonstrated – for the first time – that poly(ethylene) ( = 1 400 as well as 2 800 g · mol⁻¹, PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels‐Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) ( = 4 600 g · mol⁻¹, PDI = 1.10) and poly(styrene) ( = 6 300 g · mol⁻¹, PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin‐2‐yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high‐temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non‐poly(ethylene) containing segment via filtration of the poly(ethylene)‐containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead – depending on the block copolymer type – to the occurrence of retro Diels‐Alder processes. The present study thus demonstrates that RAFT‐HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.

     

RAFT Mediated Polymerization of Methyl Methacrylate Initiated by Bergman Cyclization: Access to High Molecular Weight Narrow Polydispersity Polymers

The first RAFT mediated polymerization of methyl methacrylate initiated by diradicals derived from Bergman cyclization was performed employing 3,4‐benzocyclodec‐3‐ene‐1,5‐diyne (BCDY) as diradical source and cyanoisopropyldithiobenzoate (CPDB) as RAFT agent. The polymerization was conducted in bulk at 80 °C for 3 h. The concentration of the enediyne was kept constant at 3.0 × 10⁻² mol · L⁻¹ and the RAFT agent concentration was varied between 0.0 mol · L⁻¹ and 2.4 × 10⁻¹ mol · L⁻¹. A detailed ESI‐MS analysis reveals the absence of intramolecular termination reactions (ring formation) in the RAFT mediated system, which usually makes diradicalic initiation unfavorable. The presence of polymeric chains propagating at both ends could be confirmed. The conversion of the RAFT mediated polymerization was up to more than two times higher than the RAFT free polymerization at identical conditions. Thus, polymers with narrow polydispersities (1.1 ≤ PDI ≤ 1.5) even at very high molecular weights (near 400 000 Da) were obtained within modest reaction times.

     

Molecular Characteristics of Poly(N‐isopropylacrylamide) Separated from Nanocomposite Gels by Removal of Clay from the Polymer/Clay Network

The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N‐isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.‐%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high (=5.5 × 10⁶ g · mol⁻¹). Also, was almost constant regardless of the clay concentration (C_clay = 1–25 × 10⁻² mol · l⁻¹), even though the properties of the NC gel varied widely over this C_clay range. Comparisons of NC gels, PNIPA, and SiO₂‐NC gels indicated that the clay platelets specifically play an important role in NC gels.

     

Amplified Fluorescence Turn‐On Assay for Mercury(II) Detection and Quantification based on Conjugated Polymer and Silica Nanoparticles

An amplified fluorescence turn‐on assay for mercury(II) detection and quantification was developed. This method makes use of specific thymine/mercury(II)/thymine coordination to capture Fl‐labeled DNA onto NP surface. Addition of a cationic conjugated polymer leads to an amplified Fl signal in solution. A sigmoidal Hg²⁺ working curve is obtained at fixed [NP] with a detection limit of 0.1 × 10⁻⁶ M . However, by reducing [Hg²⁺] and [NP] simultaneously, while maintaining [Hg²⁺]:[DNA duplex] = 3:1, a linear calibration curve is observed with a detection limit of 5 × 10⁻⁹ M . The CCP‐assisted mercury(II) assay shows potential applications in environmental mercury detection and for industrial process control.

     

Crosslinkable Vesicles Self‐Assembled by Amphiphilic Hyperbranched Polyester

Summary: Amphiphilic hyperbranched polyester (H20‐AM) with methacrylate end groups was synthesized based on hyperbranched aliphatic polyester (Boltorn™ H20). Narrow‐dispersed crosslinkable vesicles were obtained by dissolving H20‐AM in water, and characterized by laser light scattering and TEM. The hollow structural vesicle is composed of around 350 H20‐AM molecules, having a radius of around 40 nm and of 1.9 × 10⁶ g · mL⁻¹. The vesicles were fixed by crosslinking of methacrylate groups to form shape‐persistent structures.

TEM images of the crosslinked vesicles at lower magnification.     

Cellular Evaluation of Synthesized Insulin/Transferrin Bioconjugates for Oral Insulin Delivery Using Intelligent Complexation Hydrogels

Insulin transport across the epithelial cell layer in the small intestine was studied using insulin/transferrin conjugates with and without the presence of P(MAA‐g‐EG) microparticles in contact with a co‐culture of Caco‐2/HT29‐MTX cells. The insulin/transferrin conjugate was shown to increase transport relative to pure insulin by a factor of 7, achieving an apparent permeability of 37 × 10⁹ cm · s^?1. The presence of P(MAA‐g‐EG) microparticles increased conjugate transport by a factor of 14 times relative to insulin, achieving an apparent permeability of 72.8 × 10⁹ cm · s^?1. The presence of the microparticles in solution was found to improve conjugate transport by nearly 100% with little to no change in cell monolayer integrity.

     

A New Disubstituted Polyacetylene for the Detection of α‐Amino Acids

New imidazole‐functionalized disubstituted polyacetylene was synthesized by utilizing the postfunctional strategy. In addition, its ability to sense copper ions and α‐amino acids by fluorescence quenching has been studied. The quenching of the fluorescence of the imidazole‐functionalized disubstituted polyacetylene was observed at a very low level of Cu²⁺ (7.0 × 10⁻⁷ mol · L⁻¹). The fluorescent intensity decreased rapidly upon the increase of the concentration of the added solution of Cu²⁺. It was expected that the addition of α‐amino acids to the solution of the polyacetylene/Cu²⁺ complex could turn on the fluorescence of the polyacetylene, if α‐amino acids could remove the copper ions from the complex. Glycine, was used for testing: upon the addition of glycine the quenched fluorescence of P1 turned on immediately. The detection limit was as low as 6.0 × 10⁻⁵ mol · L⁻¹.

     

Greatly Enhanced Energy Density and Patterned Films Induced by Photo Cross‐Linking of Poly(vinylidene fluoride‐chlorotrifluoroethylene)

Greatly enhanced energy density in poly(vinylidene fluoride‐chlorotrifluoroethylene) [P(VDF‐CTFE)] is realized through interface effects induced by a photo cross‐linking method. Being different from nanocomposites with lowered dielectric strength, the cross‐linked P(VDF‐CTFE)s possess a high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J · cm⁻³. Moreover, patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF‐based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non‐volatile ferroelectric memory devices.

     

Simple Silole‐Containing Polyfluorene for White Electroluminescence with Simultaneous Blue,Green, and Red Emission

Novel conjugated silole‐containing polyfluorenes, with green‐ and red‐emissive siloles on the backbone of the blue‐emissive polyfluorene are synthesized for white light electroluminescence (EL) from a single polymer with simultaneous red, green, and blue (RGB) emission. The CIE coordinates (0.33, 0.36) of the white light EL spectra are very close to that for pure white light (0.33, 0.33). The EL spectra are also quite stable at different applied voltages or brightness. The relative intensities for the three RGB peaks, at 450, 505, and 574 nm, were 0.94, 1, and 0.97, respectively, which demonstrates a balanced simultaneous RGB emission. A maximum luminous efficiency of 2.03 cd · A⁻¹ for a brightness of 344 cd · m⁻², and a luminous efficiency of 1.86 cd · A⁻¹ for a more practical brightness of 2 703 cd · m⁻², were achieved.