Single step synthesis of poly(3‐octylthiophene)/multi‐walled carbon nanotube composites and their characterizations

The transport properties of conducting polymers are known to be greatly influenced by the chemical unsaturation surrounding the polymer backbone, besides favorable conformation of the side chains present. Polymeric composites with multi‐walled carbon nanotubes (MWNT) can provide a good conductive path at relatively low carbon contents, as these have high aspect ratio, specific surfaces and are cost effective. Hence their use in various applications such as organic LED, solar cells and supercapacitors are very much anticipated. In this respect poly(3‐octylthiophene)/MWNT composites have been prepared by an “insitu” polymerization process in chloroform medium with FeCl₃ oxidant at room temperature. The composites were characterized by Fourier Transfer Infrared spectroscopy (FT‐IR), Raman, work function and X‐ray diffraction (XRD) measurements. The results indicate only a weak π‐π interaction between the moieties, in the absence of a strong covalent bonding. The ultraviolet–visible (UV–Vis) measurements also support this view. The photoluminescence (PL) quenching indicates the effectiveness of the interface in the formation of the donor–acceptor type composite. The conductivity of the composites is followed by a four probe technique to understand the conduction mechanism. The Hall voltage measurement is followed to monitor carrier concentrations and mobilities. The impressive conductivity and mobility values encourage the utility of the composites as photovoltaic material. Copyright © 2008 John Wiley & Sons, Ltd.     

Conformation Control of Conjugated Polymers

In the past few decades, conjugated polymers have aroused extensive interest in organic electronic applications. The electrical performance of conjugated polymers has a close relationship with their backbone conformation. The conformation of the polymer backbone strongly affects the πelectron delocalization along polymer chains, the energy band gap, interchain interactions, and further affects charge transport properties. To realize a rigid coplanar backbone that usually possesses efficient intrachain charge transport properties and enhanced π–π stackings, such conformation control becomes a useful strategy to achieve high-performance (semi)conducting polymers. This minireview summarizes the most important polymer structures through conformation control at the molecular level, and then divides these rigid coplanar conjugated polymers into three categories: 1) noncovalent interactions locked conjugated polymers; 2) double-bond linked conjugated polymers; 3) ladder conjugated polymers. The effect of the conformation control on physical nature, optoelectronic properties, and their device performance is also discussed, as well as the challenges of chemical synthesis and structural characterization.     

Electrical Conductivity of Poly(3-octylthiophene)/Au Nanocomposites

Summary: The stabilizing effect of Au nanoparticles on electrical conductivity of poly(3-octylthiophene-2,5-diyl) based composite films was investigated. For the content of Au nanoparticles 1 vol %, the turning point where the conductivity starts to decrease, shifts to 110 °C, compared with 50 °C for the neat polymer. At low temperatures, the composites show the common activation energy of conductivity E_a = 0.3 eV independent of the Au nanoparticle concentration. It corresponds to the activation energy of neat polymer and suggests that the conductivity of the composite is controlled by the same mechanism.     

Low Band Gap Donor‐Acceptor Conjugated Polymer Nanoparticles and their NIR‐mediated Thermal Ablation of Cancer Cells

Low band gap D‐A conjugated PNs consisting of 2‐ethylhexyl cyclopentadithiophene co‐polymerized with 2,1,3‐benzothiadiazole (for nano‐PCPDTBT) or 2,1,3‐benzoselenadiazole (for nano‐PCPDTBSe) have been developed. The PNs are stable in aqueous media and showed no significant toxicity up to 1 mg · mL^?1. Upon exposure to 808 nm light, the PNs generated temperatures above 50 °C. Photothermal ablation studies of the PNs with RKO and HCT116 colorectal cancer cells were performed. At concentrations above 100 µg · mL^?1 for nano‐PCPDTBSe, cell viability was less than 20%, while at concentrations above 62 µg · mL^?1 for nano‐PCPDTBT, cell viability was less than 10%. The results of this work demonstrate that low band gap D‐A conjugated polymers 1) can be formed into nanoparticles that are stable in aqueous media; 2) are non‐toxic until stimulated by IR light and 3) have a high photothermal efficiency.

     

Synthesis and characterization of polyaniline/graphite conducting nanocomposites

A new method for the synthesis of exfoliated graphite and polyaniline (PANI)/graphite nanocomposites was developed. Exfoliated graphite nanosheets were prepared through the microwave irradiation and sonication of synthesized expandable graphite. The nanocomposites were fabricated via the in situ polymerization of the monomer at the presence of graphite nanosheets. The as-synthesized graphite nanosheets and PANI/graphite nanocomposite materials were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis (TGA). The conductivity of the PANI/graphite nanocomposites was dramatically increased over that of pure PANI. TGA indicated that the incorporation of graphite greatly improved the thermal stability of PANI. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1972–1978, 2004     

Synthesis of Glucose‐Containing Polyaniline by the Oxidative Polymerization of N‐Glucosylaniline

Summary: The oxidative polymerization of N‐glucosylaniline was carried out using ammonium persulfate as the oxidant in phosphate buffer. The structure of the isolated polymer was determined by ¹H NMR, ¹³C NMR, and UV‐vis spectroscopy to be the polyaniline having glucose residues attached to the general polyaniline unit. Participation of the ortho‐position of the aromatic ring in the polymerization was also confirmed by the analyses.

The oxidative polymerization of N‐glucosylaniline.     

Synthesis and characterization of fluorene and cyclopentadithiophene‐based copolymers exhibiting broad absorption for photovoltaic devices

In this study, two low bandgap copolymers composed of fluorene (Fl), cyclopentadithiophene (CDT), and 4,7‐bis(2‐thienyl)‐2,1,3‐benzothiadiazole (DBT) were synthesized, and their optical, electrochemical, and photovoltaic (PV) characteristics were investigated for applications in PV devices. The feed ratio of the Fl and CDT moieties was modulated to tune the electronic structures and resulting optical properties of the polymers. In the copolymeric structures, the Fl‐CDT unit absorbs the short‐wavelength UV/vis regions, and the CDT‐DBT (or Fl‐DBT) unit with strong intramolecular charge transfer characteristics covers the long‐wavelength visible regions. P1 exhibited a wide UV absorption spectrum covering the UV and entire visible region in the range of 300–800 nm, and P2 showed absorption covering from 300 to 700 nm. UV/vis and electrochemical studies confirmed the desirable highest occupied molecular orbital/lowest unoccupied molecular orbital levels of the copolymers with bandgaps of 1.62–1.86 eV, enabling efficient electron transfer and a high open‐circuit voltage when blending them with fullerene derivatives. When the polymers were blended with [6,6]phenyl‐C₆₁‐butyric acid methyl ester, P1 exhibited the best device performance with an open‐circuit voltage of 0.66 V, short‐circuit current of 4.92 mA cm^?2, and power conversion efficiency of 1.13% under Air Mass 1.5 Global (AM 1.5G, 100 mW cm^?2) illumination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of cyclopentadithiophene‐based low bandgap copolymers containing electron‐deficient benzoselenadiazole derivatives for photovoltaic devices

We have synthesized two cyclopentadithiophene (CDT)‐based low bandgap copolymers, poly[(4,4‐bis(2‐ethyl‐hexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(benzo[c][1,2,5]selenadiazole‐4,7‐diyl)] (PCBSe) and poly[(4,4‐bis(2‐ethyl‐hexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(4,7‐dithiophen‐2‐yl‐benzo[c][1,2,5]selenadiazole‐5,5′‐diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron‐donating CDT unit and the electron‐accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37–1.46 eV. The UV–vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor–acceptor (D–A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D–A complex using the ab initio Hartree‐Fock method with a split‐valence 6‐31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC₇₁BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short‐circuit current of 6.63 mA/cm², and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423–1432, 2010     

Novel Novolac Phenolic Polymeric Network of Chalcones: Synthesis,Characterization, and Thermal–Electrical Conductivity Investigation

A series of novolac phenolic polymeric networks (NPPN) were prepared via an acid-catalyzed polycondensation reaction of formaldehyde with chalcones possessing a p-phenolic OH group. When p-hydroxybenzaldehyde was treated with formaldehyde under the same conditions, a phenolic polymer (PP) was obtained. The resulting polymers were isolated in excellent yields (83–98%). Isolated polymers (NPPN, PP) were characterized using FTIR, TGA, and XRD. The results obtained from the TGA revealed that all prepared phenolic polymers have high thermal stability at high temperatures and can act as thermosetting materials. XRD data analysis showed a high degree of amorphousness for all polymers (78.8–89.2%). The electrical conductivities and resistivities of all chalcone-based phenolic networks (NPPN) and p-hydroxybenzaldehyde polymer (PP) were also determined. The physical characteristics obtained from the I-V curve showed that the conductivity of phenolic polymers has a wide range from ultimately negligible values of 0.09 µS/cm up to 2.97 μS/cm. The degree of polarization of the conjugated system’s carbonyl group was attributed to high, low, or even no conductivity for all phenolic polymers since the electronic effects (inductive and mesomeric) could impact the polarization of the carbonyl group and, consequently, change the degree of the charge separation to show varied conductivity values.     

Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.

     

Electrical properties and EMI shielding behavior of highly thermally stable polyaniline/colloidal graphite composites

A hybrid approach has been adopted by using a combination of colloidal graphite (CG) as a conducting filler, 5‐lithium sulfoisophthalic (LiSIPA) acid as a dopant, and polyaniline (PANI) as a matrix to prepare LiSIPA doped PANI–CG composites. The thermal stability (～300°C) and electrical conductivity (67.4 S/cm at 17.4% CG content) have been improved significantly as compared to PANI doped with conventional inorganic dopants like HCl or H₂SO₄ (130–150°C). The maximum shielding effectiveness value was found to be ?39.7 dB. X‐ray diffraction and infrared spectroscopy showed a systematic shifting of the characteristic peaks and bands with increase in the amount of CG, which indicates significant interaction exists between CG and PANI. The UV–Vis spectra showed the characteristic bands of PANI, with a shift to shorter wavelength with increase in the CG content. The interaction mechanism between doped PANI and CG in the resultant composites has been proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Polyurethane–oligo(phenylenevinylene) random copolymers: π‐Conjugated pores,vesicles, and nanospheres via solvent‐induced self‐organization

We report a new series of polyurethane–oligo(phenylenevinylene) (OPV) random copolymers and their self‐assembled nanomaterials such as pores, vesicles, and luminescent spheres. The polymers were synthesized through melt transurethane process by reacting a hydroxyl‐functionalized OPV with diurethane monomer and diol under solvent‐free and nonisocyanate conditions. The amount of OPV was varied up to 50 mol % in the feed to incorporate various amounts of π‐conjugated segments in the polyurethane backbone. The π‐conjugated segmented polymers were subjected to solvent induced self‐organization in THF or THF+water to produce variety of morphologies ranging from pores (500 nm to 1 μm) to spheres (100 nm to 2 μm). Upon shining 370‐nm light, the dark solid nanospheres of the copolymers transformed into blue luminescent nanoballs under fluorescence microscope. The mechanistic aspects of the self‐organization process were studied using solution FTIR and photophysical techniques such as absorption and emission to trace the factors which control the morphology. FTIR studies revealed that the hydrogen bonding plays a significant role in the copolymers with lower amount of OPV units. Time resolved fluorescent decay measurements of copolymers revealed that molecular aggregation via π‐conjugated segments play a major role in the samples with higher OPV content in the random block polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 46: 5897–5915, 2008     

The Introduction of Pyrrolotetrathiafulvalene into Conjugated Architectures: Synthesis and Electronic Properties

A series of new conjugated copolymers incorporating the redox‐active pyrrolo‐TTF unit has been synthesised. The properties of the polymers have been investigated by cyclic voltammetry and electronic absorption spectroscopy, revealing that the pyrrolo‐TTF behaves very differently to its thieno‐TTF variant. In comparison to thieno analogues, the band gaps of the new polymers are wider than expected due to a decrease in the polarizability of the heteratom (nitrogen vs. sulfur) and steric interactions between repeat units. Whilst the pyrrolo‐TTF units are stronger electron donors than thieno‐TTFs in related structures, the two redox active elements of the new polymers (TTF and conjugated chain) function independently under oxidative conditions.

     

Electrical conductivity of poly(ethylene terephthalate)/expanded graphite nanocomposites prepared by in situ polymerization

Nanocomposites based on poly(ethylene terephthalate) (PET) and expanded graphite (EG) have been prepared by in situ polymerization. Morphology of the nanocomposites has been examined by electronic microscopy. The relationship between the preparation method, morphology, and electrical conductivity was studied. Electronic microscopy images reveal that the nanocomposites exhibit well dispersed graphene platelets. The incorporation of EG to the PET results in a sharp insulator‐to‐conductor transition with a percolation threshold (?_c) as low as 0.05 wt %. An electrical conductivity of 10^?3 S/cm was achieved for 0.4 wt % of EG. The low percolation threshold and relatively high electrical conductivity are attributed to the high aspect ratio, large surface area, and uniform dispersion of the EG sheets in PET matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Effect of chemical modifications on the electronic structure of poly(3‐hexylthiophene)

The widespread use of poly(3‐hexylthiophene) (P3HT) in the active layers of organic solar cells indicates that it possesses chemical stability and solubility suitable for such an application. However, it would be desirable to have a material that can maintain these properties but with a smaller bandgap, which would lead to more efficient energy harvesting of the solar spectrum. Fifteen P3HT derivatives were studied using the Density Functional Theory. The conclusion is that it is possible to obtain compounds with significantly smaller bandgaps and with solubility and stability similar to that of P3HT, mostly through the binding of oxygen atoms or conjugated organic groups to the thiophenic ring. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013     

The First Conjugated Allene Polymer

A novel conjugated polymer with allene moieties in the polymer main chain, poly(4,4′‐biphenylylene‐1,3‐diphenylpropadien‐1,3‐ylene), was synthesized from 1,3‐bis(4‐bromophenyl)‐1,3‐diphenylpropadiene by dehalogenative polycondensation using Ni(cod)₂. The polymer shows good solubility in common organic solvents, good processability for making thin films, intense blue fluorescence in solution and acid sensitivity resulting in coloration. The conductivity increased by an order of 10⁴ upon exposure to trifluoroacetic acid vapor.     

Synthesis and electrical properties of polyaniline/polyaniline grafted multiwalled carbon nanotube mixture via in situ static interfacial polymerization

The mixture of polyaniline (PANi) and PANi grafted multiwalled carbon nanotube (PANi‐g‐MWNT) was prepared by a two‐step reaction sequence. MWNT was first functionalized with 4‐aminobenzoic acid via “direct” Firedel‐Crafts acylation in polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅) medium to afford 4‐aminobenzoyl‐functionalized MWNT (AF‐MWNT). Then, aniline was polymerized via an in situ static interfacial polymerization in H₂O/CH₂Cl₂ in the presence of AF‐MWNT in organic phase to yield the mixture of PANi and PANi‐g‐MWNT. The mixture was characterized with a various analytical techniques such as elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), cyclic voltammogram (CV), UV‐vis and fluorescence spectroscopies, and electrical conductivity measurement. On the basis of TGA analysis, the thermo‐oxidative stability of the mixture was markably improved compared to that of PANi homopolymer. Even after dedoping, in alkaline solution, the mixture would still display semimetallic conductivity (4.9 S/cm). The capacitance of the mixture was also greatly enhanced and its capacitance decay with respect to cycle times was significantly reduced. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1962–1972, 2010     

Sulfonated polyaniline‐graphene oxide hybrids: Synthesis and effect of monomer composition on the electrochemical signal for direct DNA detection

A variety of sulfonated polyaniline‐graphene oxide (SPAN‐GNO) nanocomposites based on GNO, aniline (ANI) and m‐aminobenzenesulfonic acid (ABSA) are prepared via changing the mole ratio of ANI to ABSA for the comparison of DNA sensing behavior. Self‐signals of SPAN‐GNO are employed for estimating the effect of preparation conditions [component, monomer composition (mole ratio of ANI to ABSA), and reaction time] on DNA immobilization and hybridization detection. Then, we find herein that the mole ratio of ANI to ABSA plays a lead role over other factors on hybridization efficiency. Meanwhile, the parallel experiments using methylene blue as the classic indicator verifies this conclusion. The results show that, by comparison with other mole ratio SPAN‐GNO nanocomposites‐modified electrodes, the mole ratio (2:3) exhibits the widest dynamic detection range from 1.0 × 10^?14 to 1.0 × 10^?6 M, as well as the lowest detection limit (3.06 × 10^?15 M). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1762–1773