Composition and spectral studies of polyaniline salts

Five different polyaniline salts have been prepared by chemical polymerization of aniline in aqueous solution of different acids. The polyaniline base was obtained from the corresponding polyaniline salt by dedoping using aqueous ammonium hydroxide solution. Electron paramagnetic, electronic absorption, infrared spectral and conductivity measurements have been performed on the polyaniline salts and polyaniline bases. This composition and the extent of dopant in polyaniline salt systems have been determined. There is no definite correlation between the conductivity and the stoichiometric ratio between the polyaniline base and the acid, and also the spin concentration.     

Preparation and ionic conductivity of poly(ethylene oxide) oligomers having thiolate groups on the chain ends

Poly(ethylene oxide) (PEO) oligomers having alkali metal thiolate groups on the chain ends (PEO _m -S⁻M⁺) were prepared as an ion conductive matrix. The molecular weight of the PEO part (m) and the content of the thiolate groups in the molecule were changed to analyze the effect of carrier ion concentration in the bulk. In a series of potassium salt derivatives, PEO₃₅₀-SK showed the highest ionic conductivity of 6.42 × 10⁻⁵ S/cm at 50 °C. In spite of a poor degree of dissociation which was derived from the acidity of the thiolate groups, PEO _m -SM showed quite high ionic conductivity among other PEO/salt hybrids. PEO _m -SM had glass transition temperatures (T _g) 20 °C lower than other PEO/salt hybrids. Lowering the T _g was concluded to be effective in providing higher ionic conductivity for PEO-based polymer electrolytes. Received: 30 April 1999 / Accepted: 20 June 1999     

Direct current conductivity studies on poly(3-methyl thiophene)

The direct current (dc) conductivity of poly(3-methyl thiophene) was measured in the temperature range of 77–300 K. The observed dc conductivity data were analyzed in the light of Mott’s variable range hopping model. Different Mott’s parameters such as characteristic temperature (T ₀), average hopping distance (R), average hopping energy (W), and density of states at the Fermi level (N [E _F ]) were evaluated. By taking the inverse of the coefficient of exponential decay of the localized states involved in the hopping process as 0.5 nm, a realistic value of density of states at the Fermi level (N [E _F ]) was obtained that agrees well with the values reported earlier for other conjugated polymers.     

Studies on synthesis and properties of poly(ferrocenyldimethylsilanes) and poly(ferrocenylmethylphenylsilanes)

Poly(ferrocenyldimethylsilane) and poly(ferrocenylmethylphenylsilane) have been prepared via the thermal ring-opening polymerization of the corresponding strained, silicon-bridged ferrocenophanes. It was found that the molecular weights of resultant polymers depend on the polymerization time. Their electrochemical behavior in aqueous electrolytes was investigated by cyclic voltammetry.     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

Synthesis and ionic conductivity of hyperbranched poly(glycidol)

A novel hyperbranched poly(glycidol) (HPG) was prepared and characterized. The synthesized HPG was used as a substrate of a polymer electrolyte. The ionic conductivity of a blend of HPG, polyurethane (PU), and salt was studied. The ionic conductivity of HPG/PU/LiClO₄ was about 6.6 × 10^?6 S · cm^?1 at 20 °C and 6.3 × 10^?4 S · cm^?1 at 60 °C. The results indicated that HPG showed higher solubility for salt than linear polyether when both had the same [O]/[Li⁺] molar ratio. The main reason was that more cavities and a lower degree of chain entanglement in HPG resulted in a lower glass‐transition temperature and were beneficial for decreasing the aggregation of salt or enhancing the ionic conductivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2225–2230, 2001     

The synthesis and characterization of monodisperse poly(acrylic acid) and poly(methacrylic acid)

A number of polyacrylic (PAA) and polymethacrylic (PMAA) acids have been synthesized by living anionic polymerization of the monomeric tert-butyl esters followed by subsequent hydrolysis of the corresponding polyesters. The necessary precautions were taken in order to assure good molecular weight control, as well as high yields in the polymerization reactions. The intermediate and final polymers were characterized by gel permeation chromatography and NMR-H¹ spectrometry.     

Preparation and proton conductivity of acid-doped 5-aminotetrazole functional poly(glycidyl methacrylate)

Proton conducting polymer membranes have become crucial due their applications in fuel cells as source of clean energy. In this work, we synthesized poly(glycidyl methacrylate) (PGMA) by conventional free radical polymerization of GMA using azobisisobutyronitrile (AIBN) as initiator. PGMA was modified with 5-aminotetrazole by ring opening of the epoxide group. The composition of the polymer was studied by elemental analysis (EA) and the structures were characterized by FT-IR and solid ¹³C NMR spectra. Thermogravimetry analysis (TG) and differential scanning calorimetry (DSC) were employed to examine the thermal stability and homogeneity of the materials, respectively. Polymers were doped with H₃PO₄ at several stoichometric ratios. The effect of doping on the proton conductivity was studied via impedance spectroscopy. Maximum proton conductivity of acid-doped PGMA-aminotetrazole was found to be 0.01 S/cm at 150 °C in the anhydrous state.     

Effect of molecular weight and temperature on the isothermal crystallization of poly(oxetane)

Poly(oxetane) fractions ranging in number-average molecular weights from 7800 to 157000 have been isothermally crystallized in the temperature range from –50 to 19 C, using dilatometric and calorimetric techniques. In both cases, reproducible isotherms were obtained with an Avrami exponent equal to three. The crystallization rate against crystallization temperature presents a maximum at –30 C. The level of crystallinity changes with molecular weight and the influence of this parameter on the rate of crystallization is pronounced. The crystallization temperature coefficient was studied using nucleation theory and it was found an slight increase in the basal interfacial free energy for the lowest molecular weight fraction. For the analysis of the temperature coefficient at the higher undercoolings, different approximations for the free energy of fusion and the transport term have been considered. The conclusion of this analysis is that, independently of these approximations, the obtained temperature coefficients are the same.     

Phase behavior at low temperature of poly(tetrafluoroethylene) by temperature-modulated calorimetry

Temperature modulated differential calorimetry (TMDSC) is used to examine the crystal-crystal transitions of poly(tetrafluoroethylene). This study gives new information about the dynamic thermal behavior of such transitions. The involvement of reversible and irreversible processes during the phenomenon is observed, which are related to the order-disorder changes occurring during the transition.This study adds a new example to the response of TMDSC during first order transitions.     

Synthesis and characterization of poly(vinylpyrrolidone-co-vinylphosphonic acid) copolymers

Radical copolymerizations of 1-vinyl-2-pyrrolidone (VP) with vinylphosphonic acid (VPA) at different feed ratios were investigated. The copolymers were characterized by ¹H-NMR, ¹³C-NMR and FT-IR. The copolymer composition was determined from the elemental analysis. Thermogravimetric analysis (TG) illustrates that the copolymers are stable up to 200 °C. Temperature dependence of the alternating current (AC) conductivities were investigated by means of impedance spectroscopy. The direct current (DC) conductivities of the samples are derived from the AC conductivity data.     

Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

Novel Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide),PEG-b-(PNIPAM)_2,were successfully synthesized through atom transfer radical polymerization(ATRP).A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether(PEG).The copolymers were obtained via the ATRP of N-isopropylacrylamide(NIPAM) at 30℃with CuCl/Me_6TREN as a catalyst system and DMF/H_2O(v/v = 3:1) mixture as solvent.The resulting copo...     

Conformational studies on poly(ethacrylic acid) in aqueous salts by potentiometric,viscometric, optical and1H-NMR measurements

The conformation of poly(ethacrylic acid) was studied in aqueous salts by means of potentiometric, viscometric, optical and¹H-NMR measurements. The modified potentiometric titration curves in aqueous NaCl at ionic strengths 0.01–0.3 and 5–35 °C indicated the pH-induced conformational transition from the compact to extended coil. The standard free energy changes and the difference in molar heat capacity between the two conformers were estimated from the potentiometric data. The viscometric and optical behaviours did also show the existence of the compact form at acid pH's and the pH-induced conformational transition to the extended coil in aqueous NaCl and NaClO₄. From comparison with the data for poly(methacrylic acid), the results were concluded to be consistent with the existence of the compact form stabilized by hydrophobic interaction between ethyl groups. The methyl widths in 400 MHz¹H-NMR spectra indicated that the side chains in the polymer in the compact form are in a more restricted motional state than in the coil form. Intermolecular aggregations were found at very low degrees of ionization of carboxyl groups.     

The effect of free radical reactions on structure and properties of poly(lactic acid) (PLA) based blends

The blending of PLA with poly(butylene-adipate-co-terephthalate) (PBAT) is a promising strategy to achieve a toughened multiphase material. The blends ductility could be further improved through reactive compatibilization, i.e. inducing the formation of comb PLA-PBAT copolymers during the melt blending. In the present work a non-selective strategy was adopted which consisted in the use of a peroxide, 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane. The phase morphology development and the final properties (torque, fluidity in the melt, tensile behaviour, thermal and dynamical-mechanical features) of the blends were studied as a function of the peroxide concentration. The elongation at break was improved up to a maximum value thanks to this approach and a corresponding minimum was observed in the value of the dispersed phase diameter. A structural characterization of the macromolecules formed during the reactive process was attempted by using size exclusion chromatography of the blends and comparison with the pure polymers obtained by processing in the presence of the peroxide.     

Aggregation behavior of poly(N-isopropylacrylamide) microspheres

Electrophoretic mobility and aggregation in suspensions of three types of microspheres (Ms 1, Ms 2 and Ms 3) are studied at different pH, ionic strengths and temperatures of the medium. Here Ms 1 is a core particle composed of poly(N-isopropylacrylamide-co-styrene). Ms 2 is a core-shell microsphere consisting of Ms 1 as the particle core covered with a surface layer of poly(N-isopropylacrylamide) hydrogel. Ms 3 is also a core-shell microsphere composed of MS-1 covered with a surface layer of poly(N-isopropylacrylamide-co-acrylic acid) hydrogel. The charge density zN and the softness parameter 1/λ of the microspheres were obtained from the electrophoretic mobility data on the basis of an electrokinetic theory of soft particles. It is shown that when zN is large, suspensions of microspheres are always stable, showing no aggregation. When zN is small, the suspensions are stable for large 1/λ but show strong aggregation for small 1/λ.     

Comparative studies of chemically synthesized polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid

Polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid (p-TSA) were synthesized by in situ chemical polymerization method using ammonium per sulphate as an oxidizing agent. This is a novel polymerization process for the direct synthesis of emeraldine salt phase of the polymer. The polymers were characterized by using UV-Vis and FT-IR spectroscopy, SEM, elemental analyzer, TGA/DSC and conductivity measurements. Thermal analysis shows that poly(o-toluidine) is less thermally stable compared to polyaniline. The less conductivity in poly(o-toluidine) is due to the cumulative steric as well as electronic effect of the bulky methyl substituent present on the benzene ring. High temperature conductivity measurements show ‘thermal activated behavior’.     

Crystallization behavior and biodegradation of poly(3-hydroxybutyrate) and poly(ethylene glycol) multiblock copolymers

Block copolymerization by using isocyanates is an effective method for incorporating PHB and PEG because it can prepare copolymers with good properties, such as toughness, strength, and so on. In this study, we adopted soil suspension system to estimate the biodegradability of a series of PHB/PEG multiblock copolymers with different compositions and block lengths. In the degradation process, the changes in weight loss, molecular weight, and tensile strength were periodically measured to determine the biodegradability, and the surface morphology was also observed by SEM. In contrast to pure PHB, the weight loss of the copolymer was relatively lower. On the other hand, the tensile strength and molecular weight experienced apparent decrease, and for BHG1000-3-1, they reached 46.7% and 77.7% of the initial value, respectively. SEM observation showed that the surface was covered with numerous erosion pits. All these indicate that the degradation indeed took place and long-chain molecules have been hydrolyzed into shorter ones. The crystallization behavior was also investigated by DSC and WAXD. The results showed that both the segments, PEG and PHB, can form crystalline phases at lower PHB contents ranging from 29% to 44%, and when PHB component was more than 60%, only PHB phase can crystallize.     

The effect of reaction time on the chain structure of poly(p-phenylene) and a study of doping with FeCl3

This paper deals with the relation between polymerization time and poly(p-phenylene) (PPP) yield in the synthesis of PPP by the Kovacic method. It is found that the reaction is uniform in the polymerization time range of less than 2 hr, with a PPP yield of up to about 60%, and then the yield increases a little with an increase of polymerization time. It has been found from the infrared spectra that the mainchain structure of PPP obtained from different polymerization times is exactly the same without orthoand meta-polymers. However there is a chlorine substitution for hydrogen on the phenyl rings, and the substitution quantity increases with the extension of reaction time. The reason why there is a great difference in conductivity appears with FeCl₃ doping is also studied, and we find it is related to different degrees of rinsing in the doping process.     

Synthesis and anhydrous proton conductivity of poly(5-vinyltetrazole) prepared by free radical polymerization

5-Vinyltetrazole (VT)-based polymer is mainly produced by ‘click chemistry’ from polyacrylonitrile due to the unavailability of 5-vinyltetrazole monomer, which usually produces copolymers of VT and acrylonitrile rather than pure poly(5-vinyltetrazole) (PVT). In present work, VT was synthesized from 5-(2-chloroethyl)tetrazole via dehydrochlorination. A series of PVT with different molecular weight were synthesized by normal free radical polymerization. The chemical structures of VT and PVT were characterized by ¹H NMR and FTIR. PVT without any doped acid exhibits certain proton conductivity at higher temperature and anhydrous state. The proton conductivity of PVT decreases at least 2 orders of magnitude after methylation of tetrazole. PVT and PVT/H₃PO₄ composite membranes are thermally stable up to 200 °C. The glass transition temperature (T_g) of PVT/xH₃PO₄ composite membranes is shifted from 90 °C for x = 0.5 to 55 °C for x = 1. The temperature dependence of DC conductivity for pure PVT exhibits a simple Arrhenius behavior in the temperature range of 90–160 °C, while PVT/xH₃PO₄ composite membranes with higher H₃PO₄ concentration can be fitted by Vogel–Tamman–Fulcher (VTF) equation. PVT/1.0H₃PO₄ exhibits an anhydrous proton conductivity of 3.05 × 10⁻³ at 110 °C. The transmission of the PVT/xH₃PO₄ composite membrane is above 85% in the wavelength of visible light and changes little with acid contents. Thus, PVT/xH₃PO₄ composite membranes have potential applications not only in intermediate temperature fuel cells but also in solid electrochromic device.     

Tuning the glass transition of siloxane-based poly(ionic liquid)s towards high ion conductivity

Herein, we report a simple and versatile synthetic approach towards siloxane-based poly(ionic liquid)s (PILs) with unusually low glass transition temperatures (T_g) down to −73°C, and thus “liquid-like” behavior at room temperature. We designed a polydimethylsiloxane-derived copolymer carrying dialkylimidazolium moieties, and by careful selection of the side-chain length and the type of anions we were able to manipulate its T_g over a wide range and reach high ionic conductivities (σ_DC) up to 4.8 × 10⁻⁵ S/cm at 300 K. The ionized species make up only a minor fraction (<25 mol%) of the overall repeating units and are supposedly randomly distributed: Yet our results indicate dramatic effects on the thermal properties due to repulsive interactions between ionic and non-ionic segments.