Conductance and capacitance–frequency characteristics of polypyrrole/p‐type silicon structures

We formed a polypyrrole/p‐type silicon device by an anodization process. An aluminum electrode was used as an ohmic contact. From the current–voltage characteristics of the device, barrier height and ideality factor values of 0.662 eV and 1.734, respectively, were obtained from a forward‐bias current–voltage plot. Low capacitance–frequency and conductance–frequency measurements from 0.00 to 0.30 V with steps of 0.02 V were made. At each frequency, the measured capacitance decreased with increasing frequency because of a continuous distribution of the interface states in the frequency range of 5.0 Hz to 2.0 MHz. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1334–1338, 2003     

Current–voltage and capacitance–voltage characteristics of the ITO/polyaniline doped boron trifloride/Al Schottky diode

The electrical characteristics of the ITO/polyaniline (PANI) doped boron trifloride (BF₃)/Al Schottky diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) methods. The diode indicates a rectification behavior with the ideality factor of 4.78. An ideality factor higher than unity can result from the interface state and electronic properties of the PANI doped BF₃ organic semiconductor. The barrier height of the diode was determined from both I–V and C–V characteristics. The barrier height obtained from the C–V measurements is higher than that obtained from the I–V measurements. At higher forward bias voltages, the space charge‐limited current is the dominant transport mechanism, whereas at reverse bias voltages, the current flow in the ITO/PANIBF₃/Al diode is controlled by Schottky emission mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Fabrication and electrical characterisation of the Ti/GaTe/p-Si device under 18 MeV electron irradiation

We deposited GaTe thin films with electrochemical growth technique on p-Si (100) substrate and investigated their structural and electrical properties. The electrical characteristics of the Ti/GaTe/p-Si/Al Schottky diode (SD) were determined by means of I–V (current–voltage) and C–V (capacitance–voltage) measurements. The diodes were irradiated with high energy (18 MeV) and low doses (1.38 × 10¹⁰ e^? cm^?2) electrons. The ideality factor values for Ti/GaTe/p-Si/Al structure were calculated as 1.27 and 1.53 and the barrier heights have been obtained as 0.739 and 0.706 eV from I–V measurements before and after each electron irradiations, respectively. Also, the parameters such as built-in potential, Fermi levels, acceptor concentration and barrier height of the Ti/GaTe/p-Si/Al SD have been calculated by the help of C–V measurements before and after each irradiations. The change in parameters was interpreted by the defect formation at the interface due to the electron irradiation.     

Preparation,characterization, and mechanical properties of microcellular poly(aryl ether ketone) foams

High‐performance microcellular closed‐cell foams were prepared by a two‐stage batch foaming process from fluorinated poly(ether ether ketone) and characterized by scanning electronic microscopy, tensile, and dynamic mechanical analysis (DMA). The effects of saturation pressure and temperature on the cell size, cell density, and bulk density of porous materials had been discussed. The resulting materials had average cell diameters in the range 3–17 μm, and cell densities (N_f) in the order of 0.6 × 10⁹–1.39 × 10¹⁰ cells/cm³. The porosity (V_f) was in the range of 0.2–0.85. In contrast, experimental values of Young's moduli were in good agreement with theoretically predicted values, but the relative strengths were somewhat lower than that predicted. The relaxation mechanism of microcellular was systematically investigated by DMA. The dynamic mechanical spectrometry showed that the storage modulus curve at high temperature region appeared a peak and the loss modulus was lower as compared to their solid counterparts. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 173–183, 2007     

Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006     

Synthesis,characterization, and electrical properties of polypyrrole/multiwalled carbon nanotube composites

Size‐controllable polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites have been synthesized by in situ chemical oxidation polymerization directed by various concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB). Raman spectra, FTIR, SEM, and TEM were used to characterize their structure and morphology. These results showed that the composites are core (MWCNT)–shell (PPy) tubular structures with the thickness of the PPy layer in the range of 20–40 nm, depending on the concentration of CTAB. Raman and FTIR spectra of the composites are almost identical to those of PPy alone. The electrical conductivities of these composites are 1–2 orders of magnitude higher than those of PPy without MWCNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6449–6457, 2006     

Radiation effects on SBR–EPDM blends: A correlation with blend morphology

The effect of γ radiation on the morphological and physical properties of Styrene–butadiene rubber (SBR) and Ethylene–propylene–diene monomer (EPDM) blends has been investigated. An attempt has been made to establish a correlation between various parameters like Gordon–Taylor parameter (k), hydrodynamic interaction parameter (Δ[η]_mix), chemical shift factor (b), Charlesby–Pinner parameter (p₀/q₀) and polymer–polymer interaction parameter (χ). The results showed a close dependence of mechanical and physical properties of irradiated blends on these parameters. The probability of spur overlap has been found to increase with the increase in EPDM content in the blends, which in turn results in significant improvement in the mechanical properties of the irradiated SBR–EPDM blends with higher EPDM fraction. The efficiency of four multifunctional acrylates as crosslinking aid for the radiation‐induced vulcanization of SBR–EPDM blend was also studied. The results established lower efficiency of methacrylates over acrylates in the process and indicated that among the crosslinking agents studied trimethylolpropane triacrylate is the most efficient one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1676–1689, 2006     

Synthesis and radical polymerization behavior of bifunctional vinyl monomer derived from N‐vinylacetamide and p‐chloromethylstyrene

The radical polymerization of N‐(p‐vinylbenzyl)‐N‐vinylacetamide ( 1 ) prepared by the reaction of N‐vinylacetamide with p‐chloromethylstyrene was carried out by using radical initiators such as AIBN or BPO in benzene, chlorobenzene, or bulk. As a result, poly 1 was successfully isolated by dialysis (yield, 10–36%). The crosslinking reaction of poly 1 was carried out at 60–100 °C for 8 h. By using a radical initiator such as AIBN or BPO (3 mol %), the crosslinking reaction proceeded (yield, 63–79%). Moreover, the crosslinking reaction of poly 1 proceeded at 100 °C without a radical initiator in 50% yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2714–2723, 2006     

Enhancing the electroluminescent efficiency of poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene}/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) polyblends by the introduction of chemical bonding through a thermal treatment

A significant improvement in the electroluminescence (EL) properties was observed for a poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene} (MEH–PPV)/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) (DPO–PPV) blend after a thermal treatment at 200 °C for 2 h in vacuo to furnish the chemical bonding between polymer chains. ¹H NMR spectroscopy and two‐photon excitation microscopy revealed that the chemical bonding turned the immiscible polyblend into a system more like a block copolymer with a vertically segregated morphology. Because both the lowest unoccupied molecular orbital and highest occupied molecular orbital levels of MEH–PPV in the wetting layer were higher than those of DPO–PPV in the upper layer, the heterojunction between the two layers of the polymers fit the category of so‐called type II heterojunctions. As a result, the turn‐on voltage of the polymer light‐emitting diode prepared with the thermally treated polyblend decreased to ～0.6 V, and the EL emission intensities and quantum efficiencies increased to about 4 times those of the untreated polyblend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 62–69, 2006     

Morphology and interactions of polymer brush‐coated spheres in a polymer matrix

Using a real space implementation of the self‐consistent field theory, we calculated the morphology and interactions of spherical nanoparticles with radius R_p that are grafted by polymer chains of N monomers immersed in a chemically identical polymer melt of polymerization index P. The calculation shows that, for big particles (R_p ? N^1/2a, with a the segment size), the interactions and density profiles of the grafted layers are that of brushes at flat interface; While for small particles (R_p ? N^1/2a), the interactions and density profiles are characteristic of star polymers. In the case of intermediate grafted chain lengths, that is, R_p ～ N^1/2a, we found that the grafting density of the polymers and the radius of the spherical nanoparticles are both important in determining the structure and interactions of the grafted layers. Our findings suggest possible ways to tailor the structure and interactions of the nanoparticles to benefit the fabrication of polymeric nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2811–2820, 2006     

Synthesis and characterization of a novel electroluminescent polymer based on a phenoxazine derivative

We report the preparation of a new electroluminescent polymer by the oxidative coupling copolymerization of N‐(4‐n‐butylphenyl)phenoxazine and 9,9‐di‐n‐butylfluorene with ferric(III) chloride. The reaction yields soluble polymers with a weight‐average molecular weight as high as 9000. The reactivity has been studied with respect to the reaction time, temperature, and feed ratio of the comonomers. Under optimum conditions, a copolymer with a 50% comonomer incorporation ratio can be obtained in a 75% yield. The polymers have been characterized with differential scanning calorimetry, cyclic voltammetry, and optical spectroscopy. A simple single‐layer light‐emitting‐diode device of an indium tin oxide/polymer/Mg–Ag structure shows a luminance of 200 cd/m² at an 18‐V operating voltage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4338–4345, 2006     

Synthesis and photovoltaic properties of conjugated D–A copolymers based on thienyl substituted pyrene and diketopyrrolopyrrole for polymer solar cells

A new donor‐acceptor conjugated copolymer (PDTPyDPP), comprising 2,7‐di‐2‐thienyl‐4,5,9,10‐tetrakis(hexyloxy)pyrene as a donor and diketopyrrolopyrrole (DPP) as an acceptor, was synthesized. PDTPyDPP showed good solubility in common organic solvents, broad visible absorption from 300 to 900 nm, and a moderate hole mobility up to 6.3 × 10^?3 cm² V^?1 s^?1. The power conversion efficiency of the photovoltaic device based on the PDTPyDPP/PC₇₁BM photoactive layer reached 4.43% with 0.66 V of open‐circuit voltage (V_oc), 10.52 mA cm^?2 of short‐circuit current (J_sc) and 64.11% of fill factor. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3198–3204     

Poly(N,N‐dimethylacrylamide) hydrogels obtained by frontal polymerization

Frontal polymerization (FP) has been used as an alternative technique for the preparation of poly(N,N‐dimethylacrylamide) hydrogels. Samples were synthesized in bulk, water, or dimethyl sulfoxide (DMSO), and the obtained materials were characterized and compared in terms of their yield, swelling behavior, thermal properties, and morphology. It was found that their features are dependent on the presence and type of the solvent used. Samples prepared in bulk are characterized by the lowest yields and the highest front temperatures (T_max) and velocities (V_f), whereas those synthesized in water have the highest yields and the lowest values of T_max and V_f. No significant differences have been found in terms of T_g among the three series of samples. By contrast, the reaction conditions influenced the porous morphology of the samples and, consequently, their swelling capability in water. The swelling ratio ranges from about 670–700% for some samples prepared in water up to 3500% for a sample obtained in DMSO, thus indicating that this parameter can be properly tuned by using the most suitable FP conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1422–1428, 2009     

Synthesis,characterization, and thermal properties of a novel pentaerythritol‐initiated star‐shaped poly(p‐dioxanone)

A novel star‐shaped poly(p‐dioxanone) was synthesized by the ring‐opening polymerization of p‐dioxanone initiated by pentaerythritol with stannous octoate as a catalyst in bulk. The effect of the molar ratio of the monomer to the initiator on the polymerization was studied. The polymers were characterized with ¹H NMR and ¹³C NMR spectroscopy. The thermal properties of the polymers were investigated with differential scanning calorimetry and thermogravimetric analysis. The novel star‐shaped poly(p‐dioxanone) has a potential use in biomedical materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1245–1251, 2006     

Polymerization of aniline by copper‐catalyzed air oxidation

A novel method for preparing organosoluble and conducting polyaniline (PANI) is presented. It is demonstrated that Cu(II) is an excellent catalyst for the polymerization of aniline by air oxygen in aqueous emulsions. Reactions carried out at 0 °C or at room temperature yield PANIs of reasonably high molecular weights (number‐average molecular weight = 23,000–114,000 Da) in an emeraldine base form that are soluble in many organic solvents, such as tetrahydrofuran, dimethylformamide, N‐methylpyrrolidinone, chloroform, and acetone. Spectroscopic investigations (ultraviolet, Fourier transform infrared, and ¹H NMR) have shown that PANI obtained by this procedure has the same structure as those prepared by the conventional persulfate oxidation method. The resulting PANIs show reasonable electronic conductivities (0.067–0.320 S cm^?1) upon doping with p‐toluenesulfonic acid or dodecyl benzene sulfonic acid. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6025–6031, 2006     

Novel network morphology of poly(p‐oxybenzoyl)

Polymerization of 4‐acetoxybenzoic acid (ABA) with 3,5‐diacetoxybenzoic acid (DABA) was examined to control the morphology of poly(p‐oxybenzoyl) (POB). Polymerizations were carried out at a concentration of 1.0% in an aromatic solvent Therm S‐1000® (mixture of dibenzyltoluene) at 320 °C. Polymerization of ABA yielded the POB fibrillar crystals, but the polymerization with DABA at a concentration in the feed (χ_f) of 0.10–0.15 afforded novel network structures comprised of spheres connected by fibrillar crystals. The diameter of the spheres prepared at χ_f of 0.15, which were 0.7 and 5.0 μm, showed bimodality. The network distance, fibril length, and fibril width were 6.1, 2.6, and 0.1 μm, respectively. They possessed high crystallinity. The network structure was formed as follows. Co‐oligomers were first precipitated in the beginning of the polymerization by liquid–liquid phase separation to form the microdroplets. The fibrillar crystals were formed in the coalesced spheres by the crystallization of oligomers induced by the increase of molecular weight. The fibrillar crystals connecting the spheres gradually appeared owing to the shrinkage of the spheres. The fibrillar crystals grew from the surface of the spheres with the crystallization of homo‐oligomers of 4‐oxybenzoyl units, and finally the network structure was completed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1624–1634, 2005     

Strength of polymer phase boundaries with large interfacial width: Effects of interfacial profile and phase separation morphology

In this study, we investigate the effect of random copolymer additives on the interfacial profile, the lateral phase separation morphology, and the interfacial fracture toughness (G_c) between two immiscible polymers. The interface between polystyrene (PS)/poly(methyl methacrylate) (PMMA) was reinforced with a random copolymer mixture when two or more PS_f ‐r‐PMMA_1‐f random copolymers with different volume fraction, f, were blended. For short annealing time (<3 h), the random copolymer mixture exhibits a disordered and large domain structure (>1 lm) from which crazes can be extensively initiated and developed, leading to a large interfacial fracture energy. With increasing annealing time, the random copolymer mixture self‐organizes as multiple layers, with the composition that changes gradually from PS‐rich layers to PMMA‐rich layers across the interface, leading to a large interfacial width. However, within each layer, the random copolymer mixture microphase separates laterally into smaller domains (<200 nm). We found that the microphase‐separated domains with nanometer‐sized structure significantly affect the stability of craze fibrils that can be initiated and widened at the interface, leading to a decrease in the fracture energy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1834–1846, 2010     

Polythiophenes bearing electron‐withdrawing groups in the side chain and their application to bulk heterojunction solar cells

Soluble polythiophenes bearing strong electron withdrawing groups, dicyanoethenyl [? CH?C(CN)₂] (PTDCN) and cyano‐methoxycarbonylethenyl [? CH?C(CO₂Me)CN] (PTCNME), in the side chains have been prepared. Optical band gaps calculated from onset absorption were 1.70 eV and 1.73 eV for PTDCN and PTCNME, respectively. Highest occupied molecular orbital energy levels measured with a surface analyzer (AC‐2) were ?5.53 eV and ?5.29 eV for PTDCN and PTCNME, respectively, which were much lower than that of poly(3‐hexylthiophene) (?4.81 eV). To investigate photovoltaic properties, bulk heterojunction polymer solar cells based on PTDCN and PTCNME were fabricated with a structure of ITO/PEDOT:PSS/active layer/LiF/Al, where the active layer was a blend film of polymer and [6,6]‐phenyl C₆₁ butyric acid hexyl ester (PC₆₁BH). Solar cell parameters were estimated from current density–voltage (J–V) characteristics under the illumination of AM1.5 at 100 mW/cm². The solar cell based on the blend film of PTCNME:PC₆₁BH (1:1) showed power conversion efficiency (PCE) of 0.72% together with the open current voltage (V_oc) of 0.61 V, the short current density (J_sc) of 3.90 mA/cm², and the fill factor of 30.3%. The PCE of a solar cell fabricated from PTDCN in a similar way was 0.56%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Copolymerization of poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) with designed molecular structure by a solid‐state polymerization method

Poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) (PVA‐g‐PPDO) with designed molecular structure was synthesized by a solid‐state polymerization. The solid‐state copolymerization was preceded by a graft copolymerization of PDO initiated with PVA as a multifunctional initiator, and Sn (Oct)₂ as a coininitiator/catalyst in a homogeneous molten state. The polymerization temperature was then decreased and the copolymerization was carried out in a solid state. The products prepared by solid‐state polymerization were characterized by ¹H NMR and DSC, and were compared with those synthesized in the homogeneous molten state. The degree of polymerization (D_p), degree of substitution (D_s), yield and the average molecular weight of the graft copolymer with different molecular structure were calculated from the ¹H NMR spectra. The results show that the crystallization process during the solid‐state polymerization may suppress the undesirable inter‐ or intramolecular side reactions, then resulting in a controlled molecular structure of PVA‐g‐PPDO. The results of DSC measurement show that the molecular structures determine the thermal behavior of the PVA‐g‐PPDO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3083–3091, 2006     

Polymer solar cells based on quinoxaline and dialkylthienyl substituted benzodithiophene with enhanced open circuit voltage

A poly[benzodithiophene‐alt‐di‐2‐thienyl‐quinoxaline] series (PBDTDPQ‐EH, PBDTDPQ‐OD, and PBDTDPQ‐HDT) was synthesized via Stille coupling. Deep highest occupied molecular orbital (HOMO) levels were achieved by the introduction of 2‐decyl‐4‐hexyl‐thiophen‐yl (HDT) side chains. The introduction of the various side chains increased the molecular weight of the polymers, and the polymers dissolved well in common organic solvents at room temperature. The HOMO energy level (?5.20 to ?5.49 eV) decreased because of the 2D conjugated structure. X‐ray diffraction analysis showed that PBDTDPQ‐OD had a slightly edge‐on structure. In the case of PBDTDPQ‐HDT, however, the structure was amorphous due to the thiophene side chain, and the extent of π stacking increased. After fabricating bulk‐heterojunction‐type polymer solar cells, the OPV characteristics were evaluated. The values of open‐circuit voltage (V_oc), short‐circuit current (J_sc), fill factor, and power conversion efficiency (PCE) were 0.88 V, 7.9 mA cm^?2, 45.4%, and 3.2%, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1028–1036