Electronic structure and properties of alternating donor-acceptor conjugated copolymers: 3,4-Ethylenedioxythiophene (EDOT) copolymers and model compounds

The electronic structure and properties of 3,4-ethylenedioxythiophene (EDOT) based alternating donor-acceptor conjugated copolymers and their model compounds were studied by the density functional theory (DFT) at the B3LYP level with 6-31G or 6-31G** basis set. The acceptors investigated include thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), thiadiazolothienopyrazine (TPD), quinoxaline (BP), benzothiadiazole (BD), pyrazinoquinoxaline (BPP), benzobisthiadiazole (BDD), and thiadiazoloquinoxaline (BDP). The torsional angle, intramolecular charge transfer, bridge bond length, and bond length alternation were analyzed and correlated with the electronic properties. It was found that the geometries of the donor-acceptor materials were significantly affected by the ring size and intramolecular charge transfer. The HOMO level, LUMO level, and band gap of the model compounds were well correlated with the acceptor strength. However, the electronic properties of the copolymers did not vary systematically with the acceptor strength due to the change in geometry from model compound to polymer. The aromatic geometry of EDOT-TP model compound is transformed to quinoid in the corresponding copolymer and results in a small band gap (E_g) of 0.97 eV. Large intramolecular charge transfer and the small bond length alternation in the EDOT-BDP copolymer resulted in an E_g of 0.7 eV. Hence, these two polymers could have potential applications for transparent conductors or photovoltaic devices. The small effective masses and large HOMO and LUMO bandwidths of PEDOT-TP and PEDOT-BDP make them potential materials for ambipolar thin film transistors. The theoretical results suggest that both the acceptor strength and the stable geometry contribute significantly to the electronic properties of alternating donor-acceptor conjugated copolymers.     

Synthesis of donor-acceptor poly(perylene diimide-altoligothiophene) copolymers as n-type materials for polymeric solar cells

Donor-acceptor alternated copolymers based on perylene diimide units linked in bay positions with oligothiophene units were prepared and used as acceptor material in polymeric solar cells. The copolymers have exhibited ambipolar electrochemical properties, high electronic affinities and wide electronic absorption in the visible spectrum. The spectroscopical characterization of the copolymer blends with poly-3-hexylthiophene showed evidences indicative of a charge transfer from the perylene-based copolymers to the polythiophene. All-polymeric solar cells were prepared with the blends and the photovoltaic characterization of these devices showed conversion efficiencies of 0.8% and 0.4%. The results demonstrate the potentialities of perylene-based copolymers as processable photoactive acceptor in organic solar cells.     

Synthesis of amphiphilic isoindigo co‐polymers for organic field effect transistors: A comparative study

In this work, the amphiphilic isoindigo (am‐iInd) based conjugated polymers namely poly(am‐iInd‐DT) and poly(am‐iInd‐TT) and their regular counterpart poly(reg‐iInd‐DT) and poly(reg‐iInd‐TT) were synthesized to compare their opto‐electronic and charge transport properties. They were used to fabricate organic field effect transistors. Charge transport properties in conjugated polymers depend upon intermolecular interaction which is strongly affected by the nature of side chains. The amphiphilic nature of the conjugated polymers has little impact on the charge transport properties. The charge carrier mobility of amphiphilic conjugated polymers was comparable with the regular polymers except poly(reg‐iInd‐DT) which can be correlated by X‐ray diffraction and thin film morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45461.     

Side‐chain effects on the morphology and properties of fluorene‐based alternating copolymers

Soluble fluorene‐based alternating copolymers containing benzene as the comonomer were synthesized and characterized, in which three different side chains (hydrogen atom, linear octyloxy and bulky benzyloxy groups) were attached to the phenylene ring. The effect of the side chains with different steric hindrances on the photophysical, thermal and electrochemical properties as well as the morphology were investigated. Moreover, the chain conformation and spectroscopic properties in dilute solution were studied to understand the solvent effect. Aliphatic and aromatic solvents were demonstrated to have different influences on the spectra of the polymers owing to various interaction mechanisms in the excited states. Also, a significant decrease of up to 80 °C in the thermal degradation temperature was observed as a result of the introduction of large benzyloxy units. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the polymers were estimated to be ? 5.76 to ? 5.82 eV and ? 2.19 to ? 2.27 eV, respectively, from cyclic voltammetry measurements. In addition, the electronic structures of the polymers were described via quantum chemical calculations. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of donor-acceptor type 4,4′-bis(2,1,3-benzothiadiazole)-based copolymers

A series of novel donor-acceptor type polymers based on 4,4′-bis(2,1,3-benzothiadiazole) were synthesized and characterized. Two soluble regioregular tail-to-tail and head-to-head coupled polymers, poly[7,7′-bis(3-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[3TBB3T], and poly[7,7′-bis(4-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[4TBB4T] were synthesized by FeCl₃-mediated oxidative polymerization. To further decrease the band gap of the polymers, vinylene spacers were incorporated into the polymer backbone by Stille coupling of the corresponding monomers and (E)-1,2-bis(tributylstannyl)ethene. A crystal structure of a monomer analog shows near planar arrangement of the aromatic units in the solid state. The optical properties of the monomers and polymers were investigated by steady-state absorption and photoluminescence spectroscopy. Cyclic voltammetry measurements indicate that the polymers could be employed as acceptor materials in polymer-polymer bulk heterojunction solar cells due to their low LUMO energy of about −4.0 eV. A maximum photovoltaic power conversion efficiency of about 0.3% was observed for a 1:1 blend of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly[4TBB4T] and the origin of the moderate efficiency is discussed by interpreting the device current-voltage characteristics, external quantum efficiency and incident light intensity dependence of the power conversion efficiency.     

Performance and synergistic effect of phenolic and thio antioxidants in ABS graft copolymers

The synergistic effect of phenolic and thio antioxidants on the stabilization of acrylonitrile-butadiene-styrene (ABS) graft copolymers has been studied. Three commercial antioxidants Irganox245, Irganox1076 and dilauryl thiodipropionate (DLTP) were selected. Formulations based on hindered phenols and secondary antioxidant DLTP were prepared. Stabilization was monitored in terms of changes in the functional groups (oxidation products), tensile properties and yellowness index. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were also used to assess the stability. The results indicated that the combination of Irganox245 and DLTP showed much better stabilization effect than the individual components due to the strong synergistic effect. Only weak synergism could be observed in the formulation that contained Irganox1076 and DLTP. Irganox1076 and Irgnox1076/DLTP exhibited similar behaviors between antioxidants with the highest and lowest efficiencies.     

Single crystals of crystalline block copolymers formed in n‐hexanol and methanol/DMF solutions: A comparative study

Lamellar single crystals of poly(?‐caprolactone) (PCL)‐based crystalline/liquid‐crystalline block copolymer (BCP) were prepared from two methods: solution crystallization in n ‐hexanol as well as addition of methanol dropwise to BCP/DMF solution. The crystalline morphologies of PCL single crystals prepared at different temperatures were investigated. It was observed that well‐developed single crystals were formed in n ‐hexanol at high crystallization temperatures, while low crystallization temperatures favored to fabricate well‐developed nanosheets in methanol/DMF. Annealing at the melting temperature of single crystals yielded the crystalline seeds and unimers in n ‐hexanol, while it formed spherical micelles in methanol/DMF system. As a result, the size of single crystals in n ‐hexanol could be tuned by addition of different ratios of unimer/seed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45089.     

Synthesis and characterization of alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units

A series of soluble alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units are synthesized by palladium-catalyzed Suzuki coupling reaction. All polymers demonstrate green colors of photoluminescence (PL) in chloroform, good thermal stability (with decomposition temperatures above 436 °C), and high glass transition temperatures (in the range of 120-144 °C). Owing to the large steric hindrance of diaryl substituents on bithiophenes in the polymers (P2-P4), the aggregation of solids is reduced as well as the solubility is improved, so the performance of their PLED devices are superior to that of the non-substituted polymer (P1). Compared with P1, the introduction of substitutents at 3,3′-position of bithiophene in P2-P4 has significant effects on the photophysical properties of resulting polymers in solution and solid states. Though the PL quantum yield of P1 is much higher than those of diaryl-substituted polymers (P2-P4), the PLED device of P1 has the worst electroluminescence (EL) properties due to the poor solubility of P1. Consequently, among these polymers, the device made of P3 as an emitter has the highest luminance of 2590 cd/m² at 9.5 V. For optimum device performance, a device of P3 blended with PVK can be further enhanced to a brighter luminance of 4284 cd/m² at 18 V.     

Dielectric and dynamic-mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: Polystyrene-b-poly(t-butylacrylate)

A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich- and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the α-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the α-relaxation, the relaxation map for the β-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the β-relaxations have a more local character than the α-ones. The width of the α-relaxation increases with T for all the samples, and it is slightly larger for the copolymers. The intensity of the α-relaxation is larger (between 3 and 4 times) for the homopolymer. Considering the molecular weights of the PtBa blocks, this effect has to be ascribed to the existence of frozen amorphous PtBa due to the existence of the glassy PS domains in the microphase separated copolymers.Molecular Dynamic Simulations (MDSs) for different sequences of the polymers under study were carried out. The conformational analysis was carried out between 1000 and 1700 K. The analysis of the variation of angles ?₁ and ?₂ of the ester group of PtBa points out the existence of a correlation between the conformational changes of the side group of the polymer chains and their relaxational behaviour.     

Polypyrrole–vinyl aniline modified cyclohexanone formaldehyde resin copolymers: a comparative study of the resin preparation

In this study, the synthesis of polypyrrole‐b‐vinyl aniline modified cyclohexanone formaldehyde resin (PPy‐b‐CFVAnR) block copolymers by a combination of condensation polymerization and chemical oxidative polymerization processes was examined. First, a cyclohexanone formaldehyde resin containing vinyl aniline units [4‐ vinyl aniline modified cycl?ohexanone formaldehyde resin (CFVAnR)] was prepared by a direct condensation reaction of 4‐vinyl aniline and cyclohexanone with formaldehyde in an in situ modification reaction. CFVAnR and pyrrole (Py) were then used with a conventional method of in situ chemical oxidative polymerization. The reactions were carried out with heat‐activated potassium persulfate salt in the presence of p‐toluene sulfonic acid in a dimethyl sulfoxide–water binary solvent system; this led to the formation of desired block copolymers. The effects of the oxidant–monomer molar ratio, dopant existence, addition order of the reactants, and reaction temperature on the yield, conductivity, and morphology of the resulting products were investigated. PPy‐b‐CFVAnR copolymers prepared with a resin‐to‐Py molar ratio of 1:40 showed conductivity in the range 3.7 × 10^?1 to 3.8 × 10^?2 S/cm. Oxidant‐to‐Py molar ratios of 0.5 and 1.0 were proposed to be the optimum stoichiometries for higher conductivity and yield, respectively, of the copolymer. The morphology of the copolymer (PPy‐b‐CFVAnR) was investigated with environmental scanning electron microscopy analyses. The results indicate that the surface of the copolymer was composed of well‐distributed nanospheres with average particle diameters of 60–85 nm. Also, the synthesized PPy‐b‐CFVAnR had a higher thermal stability than the pure CFVAnR. The chemical composition and structure of the PPy‐b‐CFVAnR copolymers were characterized by Fourier transform infrared spectroscopy and measurement. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42841.     

A comparative study of using allyl alcohol based copolymers in the preservation of wood: Oak vs. cedar

Wood is an important raw material that is cheap and easily worked. However, wooden objects are subject to environmental attack and mechanical shocks. In this study, our aim is to preserve wooden objects against envrironmental deterioration and mechanical shocks on to consolidate objects already degraded. Allyl alcohol (AA), acrylonitrile (AN), methyl methacrylate (MMA) and AA/AN, AA/MMA monomer mixtures were impregnated into oak and cedar. Polymerization was accomplished by gamma irradiation. The mechanical properties and the dimensional stability of the wood‐copolymer composites were determined. The presence of polymer and copolymer in the wood increased the mechanical durability of the wood. The results of the hardness tests and the compressive strengths determined in parallel and perpendicular directions to the fibers revealed that P(AA/MMA), P(AA/AN) copolymers are effective in increasing the mechanical durability of pristine‐oak and cedar woods. Similar results were also obtained from hardness tests. The decrease in the mechanical durability of pristine‐oak and cedar woods after aging for 28 days is slight. The water uptake capacity of wood + copolymer composites was observed to decrease by more than 50% compared with the original samples. In the cedar wood, where the density is low and the quantity of copolymer is high, this decrease ranged from 100% to 50%.     

Synthesis and characterization of alternating copolymers containing bipyridine and phenylene vinylene for fluorescent chemosensors

Alternating copolymers containing bipyridine and phenylene vinylene were synthesized through a Wittig condensation reaction of their corresponding diphosphonium salts and dialdehydes. The molecular weights of the resulting polymers were relatively low because of the low solubility in the reaction solvents. The optical properties of the polymers were substantially affected by the repeating units of phenylene vinylene. The absorption spectra of the copolymers in the solid state exhibited a bathochromic shift compared to those carried out in solution. The effective conjugation length could be extended with the addition of Cu²⁺, Ni²⁺, and Zn²⁺ ions into the polymer solutions in a 1 : 1 ratio of the bipyridine to the phenylene vinylene units. All of the polymer solutions behaved as a turn‐off fluorescent chemosensor upon the addition of a variety of the metal ions. The sensing behavior to various metal ions revealed that the polymers were highly sensitive to the Cu²⁺, Ni²⁺, and Zn²⁺ ions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42795.     

Comparison of methods for characterizing comonomer composition in ethylene 1-olefin copolymers: 3D-TREF vs. SEC-FTIR

In this paper, two methodologies for determining comonomer composition in ethylene 1-olefin copolymers, namely three detectors coupled to a temperature rising elution fractionation unit (3D-TREF) and size exclusion chromatography coupled to a Fourier transfer infrared detector (SEC-FTIR), are examined and compared. Because the two methods are based on different separation mechanisms, insight into the resin's molecular architecture is gained from two entirely different, yet complementary perspectives. The choice of which method to use will be determined by the specific structure vs. property issue under study. Comparative results from the analysis of copolymers produced by Ziegler-Natta, chromium and metallocene catalysts show that both the methods are useful for characterizing LLDPE resins. However, the 3D-TREF method may offer more insight into the heterogeneity of resin blends, particularly when the blend components have similar molecular weights. Although some MW-dependency information of the temperature fractions can be ascertained via viscometer and light scattering detectors, SEC-FTIR is the more appropriate method to detect compositional heterogeneity in resin blends that are composed of two or more resins with the same copolymer compositions, but with different molecular weights.     

Sintering of a sodium-based NASICON electrolyte: A comparative study between cold,field assisted and conventional sintering methods

Scandium-substituted NASICON (Na_3.4Sc_0.4Zr_1.6Si₂PO₁₂) is a promising electrolyte material for sodium-ion solid state batteries, with the highest ionic conductivity reported to date for a NASICON material. Low-temperature densification and control of microstructure are important factors to enable the low-cost manufacturing of such new battery type. Non-conventional sintering techniques such as Field Assisted Sintering Technology / Spark Plasma Sintering (FAST/SPS) and Cold Sintering are therefore investigated and compared to conventional free sintering. FAST/SPS enables to get rapidly dense samples (99% TD) at lower temperatures than the ones required by conventional sintering routes and with similar electrical properties. Cold sintering experiments, involving the addition of aqueous solutions as sintering aids and high mechanical pressure, enable a moderate densification, but at temperatures as low as 250 °C. Further heat treatments still below the conventional sintering temperature increased the achieved density and ionic conductivity.     

Shape memory effect of ethylene–vinyl acetate copolymers

Crosslinked ethylene–vinyl acetate (EVA) copolymers with VA content of 28% by weight were prepared by a two‐step method by evenly dispersing the crosslinking agent (dicumyl peroxide) into the EVA matrix and then crosslinking at elevated temperatures. The crosslinking features of the samples were analyzed by Soxhlet extraction with xylene and dynamic mechanical measurements. All the samples were crystalline at room temperature, and the chemical crosslinks seemed to have little effect on the melting behavior of polyethylene segment crystals in the EVA copolymers. The shape recovery results indicated that only those specimens that had a sufficiently high crosslinking degree (gel content higher than about 30%) were able to show the typical shape memory effect, a large recoverable strain, and a high final recovery rate. The degree of crosslinking can be influenced by the amount of the peroxide and the time and temperature of the reaction. The response temperature of the recovery effect (about 61°C) was related to the melting point of the samples. The EVA shape memory polymer was characterized by its low recovery speed that resulted from the wide melting range of the polyethylene segment crystals. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1063–1070, 1999     

Memory effects of carbon nanotube-based field effect transistors

In this paper, we report the study on the non-volatile memory effects of carbon nanotube-based field effect transistors (CNTFETs), in which semiconducting single-wall carbon nanotubes (SWNTs) bridge the gold electrodes and the doped silicon substrate acts as the back gate. We find that our CNTFETs exhibit good performance with on/off ratio of more than 10⁴ and they also show strong memory effects. Hysteretic behaviors of the drain current as a function of the gate voltage are clearly observed at room temperature. The threshold voltage shift increases with increasing the sweeping range of the gate voltage. The CNTFET memory effects show good charge retention capability with the data storage time of around 7 days at ambient condition. Besides, the threshold voltage shift of the as-prepared CNTFETs is found to decrease with time and saturate after around 3 days. Water and alcohol molecules adsorbed on the carbon nanotube are suggested to be the origin of the phenomena. It is also observed that the threshold voltage shift in “top-contact” structures is larger than those in “bottom-contact” structures at the same gate voltage sweeping range.     

Fabrication and electrical properties of MoS2 nanodisc-based back-gated field effect transistors

Two-dimensional (2D) molybdenum disulfide (MoS₂) is an attractive alternative semiconductor material for next-generation low-power nanoelectronic applications, due to its special structure and large bandgap. Here, we report the fabrication of large-area MoS₂ nanodiscs and their incorporation into back-gated field effect transistors (FETs) whose electrical properties we characterize. The MoS₂ nanodiscs, fabricated via chemical vapor deposition (CVD), are homogeneous and continuous, and their thickness of around 5 nm is equal to a few layers of MoS₂. In addition, we find that the MoS₂ nanodisc-based back-gated field effect transistors with nickel electrodes achieve very high performance. The transistors exhibit an on/off current ratio of up to 1.9 × 10⁵, and a maximum transconductance of up to 27 μS (5.4 μS/μm). Moreover, their mobility is as high as 368 cm²/Vs. Furthermore, the transistors have good output characteristics and can be easily modulated by the back gate. The electrical properties of the MoS₂ nanodisc transistors are better than or comparable to those values extracted from single and multilayer MoS₂ FETs.     

Solution study of novel diblock copolymers: Morphology and structural transition

The solution behavior and morphology of the nanostructures formed by novel block copolymers based on 1-cetyl[2-(acryloyloxy)ethyl]dimethylammonium bromide (ADHA) and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) have been studied using small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). In these block copolymers the pADHA block consists of long hydrophobic C₁₆ tails connected to a positively charged quaternary ammonium group, making it amphiphilic, while the second block is either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). Using SAXS, we demonstrate that the morphology of block copolymer nanostructures is dependent on the solute concentration and on the length and composition of the blocks. In the case of thermoresponsive pADHA-b-pNIPAM, two types of ordered structures are formed and their characteristics are also defined by the temperature. Complementary information is obtained from DLS, showing large particles with the size up to 280 nm, which is beyond the resolution of the SAXS data. Loss of ordering around the lower critical solution temperature followed by ordering restoration at the higher temperature was observed for the pADHA-b-pNIPAM block copolymers. The differences in the structural order in the block copolymer solutions are directly related to their ability to coat hydrophobic metal nanoparticles.     

Synthesis and characterization of alternating copolymers of thiophene-containing N-phenyl maleimide and styrene by photoinduced radical polymerization and their use in electropolymerization

A novel N-(4-(3-thienyl methylene)-oxycarbonylphenyl) maleimide (MBThi) monomer was synthesized by the esterification reaction of maleimidobenzoic acid (MBA) with 3-thiophene methanol. Photoinduced radical polymerization was employed to prepare the alternating copolymers of MBThi with styrene (St) at room temperature using ω,ω-dimethoxy-ω-phenylacetophenone (DMPA) as photoinitiator. Different copolymerization conditions were examined to estimate the influence of the used solvents and comonomers' total molar concentration on the conversion, the number-average molecular weight (M_n), and polydispersity index (M_w/M_n) of the resulting polymers. Thermal behavior of the alternating copolymers (PSt-alt-MBThi) was also investigated by thermogravimetrical analysis (TGA) and differential scanning calorimetry. Moreover, the obtained alternating copolymers were employed in electropolymerization experiments and random conjugated graft copolymers with thiophene or pyrrole were synthesized through their pendant thienyl groups. These polymers were characterized by cyclic voltammetry (CV), FTIR and scanning electron microscopy (SEM). Conductivity measurements were carried out by the four-probe technique.     

Resistance‐based switching humidity property of crosslinked acrylic acid–acrylamide copolymers and their ionization effect against the critical humidity

The resistance‐based switching humidity property of crosslinked acrylic acid–acrylamide copolymers was measured with an LCZ meter, and their ionic mobilities, which varied with humidity, were measured by the polar‐inversion method. Their conduction mechanism was discussed, and it was found that the ionization effect of some binding ions against a critical humidity takes place in switchable humidity‐sensitive materials. The effect is that some binding ions in materials turn into free ions when a given ambient humidity, called a critical humidity, is reached. The avalanching‐conduct electricity then occurs in materials. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1057– 1060, 2002