Effect of fast neutrons on dielectric properties of pure and gelatin doped-poly (vinyl alcohol) films

Cast thin films of pure and gelatin doped poly(vinyl alcohol) (PVA) with concentrations of 2, 5, 7, 10, and 15 wt% were prepared and subjected to fast neutron fluences in the range of 10⁵–10⁸ n/cm². The dielectric constant (ε′), dielectric loss tangent (tanδ) and a.c. electrical conductivity (σ_a,c) were investigated as a function of field frequency and temperature for all samples before and after irradiation. A clear glass transition peak was observed in ε′(T) and tanδ(T) curves. The irregular shift in the position of the glass transition temperature (T_g) in tanδ spectra with increasing neutron fluence can be attributed to either degradation or the predominance of the crosslinking process. The electric dipole moment and activation energy were calculated for pure and gelatin doped PVA samples before and after neutron irradiation.     

Miscibility of conductive blends of poly(o-anisidine) with poly(2-alkyl-2-oxazoline)s

HCl-doped poly(o-anisidine) (PANIS–HCl) and undoped poly(o-anisidine) (PANIS-base) were blended with poly(2-methyl-2-oxazoline) (PMOx) or poly(2-ethyl-2-oxazoline) (PEOx) by solution casting from dimethyl sulfoxide. Blends containing 50 wt % or less of PANIS–HCl or PANIS-base were flexible and homogeneous. The glass transition temperature of the blend continuously shifted away from that of PMOx or PEOx with increasing PANIS–HCl or PANIS-base content, indicating miscibility. The shift in the T_g value was larger for the PMOx blend than for the corresponding PEOx blend, suggesting a stronger interpolymer interaction in the former blend. Fourier transform infrared spectroscopic studies indicated the presence of specific interactions in the blends as evidenced by the changes of C=O and NH bands. Blends containing 50 wt % of PANIS–HCl showed conductivity of about 10^-4 S/cm. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:391–397, 1997     

The electrical properties of boron‐containing poly(vinyl alcohol) derived ceramic organic semiconductor

The direct and alternating current conductivity, space charge limited current, and thermoelectrical properties of boron‐containing poly(vinyl alcohol)‐derived ceramic have been investigated. The electrical conductivity of the sample increases with increase in temperature and the room temperature conductivity of the sample was found to be 3.82 × 10^?5 S/cm. The electrical conductivity and thermoelectric power results suggest that the PVAB polymer has p‐type electrical conductivity. The current–voltage characteristics indicate that at higher voltages, the space charge limited conductivity mechanism is dominant in the PVAB sample. The electronic parameters such as the position of the Fermi level bottom of the conduction band, E_F, the density of states in conduction band N_c, effective mass of holes m_s were found to be 0.44 eV, 2.12 × 10²⁵ m^?3, and 0.59 m_o, respectively. Alternating current conductivity results suggest that the correlated barrier hopping conductivity is dominant in AC conductivity mechanism of the sample. The imaginary part of the dielectrical modulus at different temperatures shows a relaxation peak, indicating a temperature‐dependent non‐Debye relaxation. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Synthesis and properties of nonlinear optical polymers based on poly(ether imides) for electrooptical devices

Summary : Nonlinear optical poly(ether imides) with an adequate thermal stability has been synthesized by direct coupling of hydroxy poly(ether imides) and NLO chromophores with a quantitative yield. The resultant amorphous NLO poly(ether imides) exhibited good solubility in common organic solvents, providing optical-quality thin films by spin coating. The glass transition temperatures of the polymers are at around 180 °C. The electrooptic coefficients (r₃₃, @1.3μm) of PEI-DR1 was 12.3 pm/V with an electrical poling field of 100 V/μm and it decayed about 10 % over 10 months at 90 °C under atmospheric conditions. Received: 23 February 1999/Revised version: 26 March 1999/Accepted: 29 March 1999     

Ru(0) complex catalyzed polyaddition New synthesis of poly(alkylenebenzoxazole) and poly(alkylenebenzimidazole)

Summary The reactions of α,ω-diyne, HC≡C(CH₂)_mC≡CH (m = 6 and 8), with 3,3'-diaminobenzidine and with 3,3'-diamino-4,4'-dihydroxybiphenyl in the presence of RU₃(CO)₁₂-PPh₃ catalyst give the corresponding poly(alkylenebenzoxazole)s and poly(alkylenebenzimidazole)s, respectively. The former polymers obtained from the equimolar reaction of the monomers are partly soluble in polar organic solvents such as DMF, DMSO, and NMP, while the poly(benzimidazole)s are soluble in these solvents. GPC measurement shows the molecular weights of the polymers, M _n of 4.8−14.1×10³ and M _w of 6.4−19.7×10³. Received: 24 November 1998/Revised version: 21 December 1998/Accepted: 24 December 1998     

Lithium ionic conductivity in poly(ether urethanes) derived from poly(ethylene glycol) and lysine ethyl ester

Poly(ether urethanes) obtained by the copolymerization of poly(ethylene glycol) (PEG) and lysine ethyl ester (LysOEt) are elastomeric materials that can be processed readily to form flexible, soft films. In view of these desirable physicomechanical properties, the potential use of these new materials as solid polymer electrolytes was explored. Solid polymer electrolytes were prepared with copolymers containing PEG blocks of different lengths and with different concentrations of lithium triflate (LiCF₃SO₃). Correlations between the length of the PEG block, the concentration of lithium triflate in the formulation, and the observed Li⁺ ion conductivity were investigated. Solid electrolyte formulations were characterized by differential scanning calorimetry for glass transition temperatures (T_g), melting points (T_m), and crystallinity. Ionic conductivity measurements were carried out on thin films of the polymer electrolytes that had been cast on a microelectrode assembly using conventional ac-impedance spectroscopy. These polymer electrolytes showed inherently high ionic conductivity at room temperature. The optimum concentration of lithium triflate was about 25–30% (w/w), resulting at room temperature in an ionic conductivity of about 10⁻⁵ S cm⁻¹. For poly(PEG₂₀₀₀-LysOEt) containing 30% of LiCF₃SO₃, the activation energy was ∼ 1.1 eV. Our results indicate that block copolymers of PEG and lysine ethyl ester are promising candidates for the development of polymeric, solvent-free electrolytes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1449–1456, 1997     

Neutral poly(3,4-ethylenedioxythiophene-2,5-diyl)s: preparation by organometallic polycondensation and their unique p-doping behavior

Neutral and non-doped poly(3,4-ethylenedioxythiophene), PEDOTh(Ni), and its hexyl derivative, PEDOTh-C₆(Ni), have been prepared by organometallic dehalogenation polycondensation of 2,5-dichloro-3,4-ethylenedioxythiophene and its hexyl derivative with a zerovalent nickel complex. PEDOTh-C₆(Ni) was soluble in organic solvents and ¹H NMR data indicated that it had an M_n of 11,000. MALDI-TOF mass analysis of PEDOTh(Ni) gave M_n and M_w of about 1700 and 2400, respectively. PEDOTh-C₆(Ni) showed a UV-Vis absorption peak at 546 nm in CHCl₃. Electrochemical oxidation of PEDOTh-C₆(Ni) started at about −0.40 V vs Ag⁺/Ag and gave a peak at 0.20 V vs Ag⁺/Ag. Chemical and electrochemical oxidation (or p-doping) of PEDOTh-C₆(Ni), both in solutions and in a solid state, led to weakening of the original π-π^∗ peaks and rise of new peak(s) in a region of 800-1500 nm. The p-doping of PEDOTh-C₆(Ni) caused not only a decrease in the intensity of ¹H NMR signals of the bridging ethylene hydrogens but also a decrease in that of the hexyl side chain, suggesting a strong interaction of the p-dopant with the side chain. NMR data of poly(3-methoxythiophene-2,5-diyl) also supported an assumption that p-doping brings about a severe change in electronic state of the substituent attached to the polythiophene main chain. PEDOTh(Ni) had a density of 1.71 g cm⁻³; the molecular packing mode of PEDOTh(Ni) is discussed based on the density of the polymer and its XRD data.     

Correlation between crosslinking efficiency and spatial inhomogeneity in poly(acrylamide) hydrogels

Summary Elasticity and light scattering measurements were carried out on poly(acrylamide) (PAAm) hydrogels prepared from acrylamide (AAm) and N,N’-methylenebisacrylamide (BAAm) monomers under various reaction conditions. Elasticity tests showed that the crosslinking efficiency of BAAm ε_xl, that is the fraction of BAAm forming effective crosslinks decreases as the initial monomer concentration C_o is decreased. At C_o=3%, ε_xl was found to be 10^-2–10^-3, indicating that 99 to 99.9% of BAAm used in the hydrogel preparation are wasted in elastically ineffective links. Debye-Bueche analysis of the light scattering data showed that, irrespective of the gel synthesis conditions, the correlation length ξ, that is, the extension of inhomogeneities in the hydrogels is 10¹ nm. The extent of frozen concentration fluctuations in the hydrogels represented by 〈η²〉 decreases with increasing crosslinking efficiency of BAAm. The combination of the light scattering and the elasticity data of gels shows a direct correlation between the fraction of wasted crosslinker molecules during gelation and the spatial gel inhomogeneity.     

Synthesis and properties of poly[2,6-(p-phenylvinyl)-4-(4'-octyloxybiphenyl-4-yl)quinoline]

Summary A novel polyquinoline (PQDBP8) containing the pendent 4'-octyloxybiphenyl group in the 4-position of the quinoline ring was prepared by the acid-catalyzed polymerization (Friedl?nder quinoline synthesis) of 1-(4-{2-[4-amino-3-(4'-octyloxybiphenyl-4-carbonyl)-phenyl]vinyl}phenyl)ethanone (6). PQDBP8 showed highly thermal stability (T_d= 384 °C, T_g= 183 °C). PQDBP8 showed blue fluorescence in dilute solution (λ_max= 449 nm) and green fluorescence in solid state (λ_max= 494, 540 nm) due to excimer formation. EL spectrum of PQDBP8 lies in the green region (λ_max= 572 nm) and PQDBP8/PVK blend film lies in the blue region (λ_max= 446 nm). Received: 16 February 1999/Revised version: 20 April 1999/Accepted: 26 April 1999     

Synthesis of light-emitting π-conjugated poly(pyrimido[5,4-d]-pyrimidine-2,6-diyl) with bulky side chains and high molecular weight

New poly(pyrimido[5,4-d]pyrimidine-2,6-diyl) (PPympym) with bulky dialkylamino substituents (-NR₂, R=hexyl, decyl) was prepared by organometallic dehalogenative polycondensation using a zerovalent Ni complex. The obtained PPympym was soluble in common organic solvents such as CHCl₃ and THF, and GPC analysis (in CHCl₃; vs. polystyrene standards) indicated that new Ppympyms had high number-average molecular weights M_n of 19,100-34,000; they also gave a high [η] value of about 2.1 dl g⁻¹. PPympym showed strong photoluminescence both in CHCl₃ and in film, and greenish-blue electroluminescence from PPympym-based double-layer light-emitting devices (ITO/PEDOTh/PPympym/Ca-Al; PEDOTh, poly(ethylenedioxythiophene)) was observed.     

Different steps in the electrosynthesis of poly(3,4-ethylenedioxythiophene) on platinum

The initial stages of poly(3,4-ethylenedioxythiophene) (PEDOTh) film growth on platinum electrodes from TBAClO₄/acetonitrile solution are investigated by means of current-time transient measurements and tapping mode atomic force microscopy. It is shown that, for growth potentials in the range 1.17-1.29 V vs. SCE, the deposition process involves the formation of oligomers in the solution, progressive nucleation of centres of the new phase and three-dimensional growth of a first compact layer followed by a non-uniform distribution of granular-like clusters, whose number and size increase with the synthesis potential and charge. The obtained results reveal that PEDOTh films prepared at distinct potentials but with the same growth charge (Q_g) display similar electroactivities. They also depict that the electrochemical behaviour of the films is a function of the charge used for the synthesis, namely the reduction of tick PEDOTh layers (Q_g > 20 mC cm⁻²) includes more that one step, as a consequence of the formation of a two-layered polymer film.     

Inverse gas chromatographic observation of thermodynamic interaction between poly (vinylidene fluoride) and organic solvents

Summary Inverse gas chromatography (IGC) has been applied to observe the interaction between poly(vinylidene fluoride) (PVDF) and organic solvent systems under conditions approaching infinite dilution of the volatile component. The specific retention volumes (V_g ⁰) were calculated from the retention volumes of the PVDF/solvent systems. The retention diagrams (RDs) which were plotted as ln V_g ⁰ vs. reciprocal temperature, corresponded with the thermodynamic behavior of PVDF. PVDF dissolves well in carbonyl-containing solvents at high temperatures. In these systems, the solution is converted easily to a thermoreversible gel by standing at room temperature. The Flory-Huggins interaction parameter (χ₁₂) and molar heat of sorption of probe absorbed by the amorphous part of PVDF (Δ H₁ ^s) calculated from the retention values indicated that the characteristics of the interaction between PVDF and the solvent (probe) varied with temperature and probe properties. The results of IGC of PVDF/solvent systems were discussed in relation to the dissolution and gelation behavior of PVDF. Received: 29 September 1999/Revised version: 30 November 1999/Accepted: 9 December 1999     

Electrical conductivity of poly(2-ethynylthiophene) and poly(2-ethynylfuran) doped with electron acceptors

The electrical conductivity of poly(2-ethynylthiophene) (P2ET) and poly(2-ethynylfuran) (P2EF) doped with electron acceptors such as iodine, bromine, and ferric chloride was investigated. The maximum electrical conductivities of P2ET and P2EF doped with iodine were 3 × 10^?4 Ω^?1 cm^?1 and 5 × 10^?3 Ω^?1 cm^?1, respectively. The electrical conductivity was nearly independent with increasing molecular weight. The spectral measurements such as UV-visible, infrared, electron paramagnetic resonance, thermogravimetric analysis, and X-ray diffraction were also carried out.     

Electrical conductivity of polyblends of poly(1,4-phenylene vinylene) and poly(2,5-dimethoxy-1,4-phenylene vinylene)

Summary A series of polyblends of poly(1,4-phenylene vinylene), PPV, and poly(2,5-dimethoxy-1,4-phenylene vinylene), PDMPV, were prepared in film form from precursor polyblends of the respective sulfonium salt polymers, which were separately prepared from the respectivebis(sulfonium salt) monomers. The blend films were doped with I₂ at room temperature to obtain a wide range of electrical conductivities (10^–2 to 10²Scm^–1) depending on the blend composition. The higher the content of PDMPV in the blends the higher was the conductivity.     

Correlations among defect type, photoconductivity and photoreactivity of doped TiO2

The electrical conductivity (σ), photoconductivity and photocatalytic reactivity in doped crystalline TiO₂ were measured as a function of the oxygen partial pressure (Po₂), temperature, doping type and UV irradiation. The Po₂ dependence of σ suggests that the predominant atomic defects in pure TiO₂ are oxygen vacancies (V _o ^... ) and interstitial titanium ions (Ti _i ^... ), but the dominant defect is changed with Po₂ and temperature. The photoexcited electrons in reduced and/or n-type doped TiO₂ enhance both the photoconductivity and the photocatalytic reactivity by the reduction process. Therefore, these behaviors are strongly dependent on the electron concentration.     

Novel high performance poly(aryl ether ketone)s based on symmetrical naphthylene isomers

Summary  Two new bisphenol monomers containing naphthylene groups were synthesized by a Friedel-Crafts acylation reaction followed by a demethylation reaction. Four naphthylated poly(aryl ether ketone)s (PANEKs) were successfully prepared via a typical nucleophilic substitution polycondensation. These PANEKs exhibited excellent properties including high T_gs (above 204^oC) and good thermal stability (the temperature at 5% weight loss in air was above 430^oC). They had improved solubility, and flexible and transparent membranes could be cast from their solutions. The good mechanical property (tensile strength of 82.2∼102.8 MPa, Young’s moduli of 2.1∼2.4 GPa, and elongation at break of 17∼31%) indicated they were strong materials. Low dielectric constant (2.8-2.9 at 1 MHz) and moisture absorptions (i<<0.45%) were also detected from the polymer films.     

Thermal analyses of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by T_o = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was T_p = 0.91B + 320, and the temperature at which degradation was completed was T_f = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), T_o = 0.96B + 308, T_p = 0.99B + 320, and T_f = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), T_o = 1.11B + 305, T_p = 1.10B + 319, and T_f = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T_o, T_p, and T_f relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001     

Processing and properties of new heteroaromatic Schiff-base poly(sulfone-ester)s and their blends

A new interesting class of linear Schiff-base poly(sulfone-ester)s has been synthesized by polycondensation of (E)-1-(4,4′-(4-hydroxy-3-chlorobenzylidene)thiocarbamoylaminophenyl-sulfonylphenyl)-3-(4-hydroxy-3-chlorobenzylidene)thiourea with 2,6-pyridinedicarbonyl chloride/thiophene-2,5-dicarbonyl dichloride. The enhancement of physical properties (thermal stability, glass transition temperature, mechanical strength, molar mass, electrical conductivity, etc.) of polymeric materials while maintaining their processability was the foremost aspiration of this research work. The pyridine or thiophene-based heteroaromatic poly(sulfone-ester)s (PSEs) showed ample solubility in amide solvents and good yield. PSEs possessed high inherent viscosity of 1.79–1.93 dL/g and molar mass 125 × 10³–145 × 10³ g mol^?1. The polymers were thermally stable with 10 % weight loss in the range 538–547 °C and glass transition temperature between 293 and 296 °C. Further aim was to obtain novel miscible nano-blends exhibiting good electrical conductivity and heat stability. For this purpose, PAN doped with dodecylbenzenesulfonic acid (PAN/DBSA) was prepared by in situ doping polymerization, and then blended in solution/melt with PSEs. The resulting high performance materials potentially combined the fine thermal properties and processability of poly(sulfone-ester)s with electrical characteristics of polyaniline. FESEM of melt-blended PSEs/PAN/DBSA showed nano-level homogeneity of the microstructure liable for better electrical conductivity (2.7–3.2 S cm^?1). The azomethine and pyridine moieties introduced in the backbone render these polymers thermally and mechanically stable as well as electrically conducting. The miscible blends, exhibited good heat stability (T ₁₀ 520–527 °C, T _g 281–285 °C) and mechanical strength (55.20–57.18 MPa) compared with reported azomethine/polyaniline-based structures. New processable and high-performance engineering plastics, attractive for aerospace applications, can be fabricated using novel blends.     

Gas permeation properties of poly(2,5-dialkyl-p-phenyleneethynylene) membranes

Dipropynylbenzenes with alkyl groups (CH₃C ≡ CRC₆H₂RC≡CCH₃, R=n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, 1a–c, respectively) were polymerized with Mo(CO)₆ to afford solvent-soluble poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c). The polymers (2a–c) had high molecular weight over 3×10⁴, and gave free-standing membranes by solution casting method. According to thermogravimetric analysis (TGA), these poly(p-phenyleneethynylene)s showed high thermal stability (T₀ ≥380 °C). The densities of membranes of poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c) were 0.936–0.965, and their fractional free volume (FFV) were relatively large (ca. 0.14–0.15). The oxygen permeability coefficients (PO₂) of membranes of 2a–c were 4.88, 7.06, and 16.6 barrers, respectively.     

Radically crosslinked branched poly(N-allylethylenimine) with lithium triflate as a solid state polymer electrolyte

Branched poly(N-allylethylenimine) (BPAEI), a solid state polymer electrolyte host, was synthesized by allylation of branched poly(ethylenimine) (BPEI). Allylation was essentially complete with the 2 and 1° nitrogen atoms of BPEI being mono-allylated and di-allylated, respectively, and with little or no quaternization. BPAEI can be radically cross-linked with and without lithium trifluoromethanesulfonate (LiTf) present to form free-standing, homogeneous, minimally hygroscopic films. BPAEI has a glass transition temperature (T_g) of −65 °C, as measured by differential scanning calorimetry (DSC), which increases with the concentration of initiator upon cross-linking using V-50 (2,2-azobis(2-amidino-propane) dihydrochloride) to −15 °C at a 10:1 nitrogen to initiator molar ratio (N:initiator). BPAEI with 20:1 N:Li⁺ (molar ratio) LiTf has a T_g of −48 °C, which increases with the concentration of radical initiator upon cross-linking using V-50 to 3 °C at 10:1 N:initiator. At compositions near 60:1 N:initiator, an unusual decrease in the rate at which T_g changes with cross-linking was observed, both with and without LiTf present, indicating that some undefined morphological changes occur. The effect of this morphological change resulted in the highest Ac conductivities at 60:1 N:initiator for all LiTf concentrations studied. At 20:1 N:Li⁺ LiTf and 60:1 N:initiator, the room temperature Ac conductivity was 1×10⁻⁸ S/cm which increased to 1×10⁻⁵ S/cm at 80 °C, the highest conductivity observed in the concentration ranges studied. Infrared spectroscopy (IR) showed that the concentrations of the individual ionic species present were largely independent of either LiTf concentration or cross-linking density, suggesting that changes in ion mobility, likely resulting from morphological changes, substantially control the ionic conductivity.