Optical properties of pure and doped polymers

This article deals with the optical properties of large bandgap polymers i. e. Polymers whose intrinsic absorption is in ultraviolet region of the spectrum. The article focuses on the optical properties of polymeric solids in the visible spectral range. In this range the above class of polymers can be considered as ‘transparent’. Many applications, such as applications for optical elements and for light fibers are based on the low optical losses of polymeric materials. The residual loss mechanisms, such as vibronic overtone absorptions and light scattering are discussed in some details. A comparison with inorganic glasses is performed, showing that materials like fused silica have lower losses than their organic counterparts. The second part of the article deals with the absorptive properties of polymers which are doped with dye molecules, absorbing in the visible range. The optical spectra of doped polymers are usually broad and structureless. It is shown how one can gain optical resolution by performing narrow-band photochemistry: Photochemical hole burning (PHB). The gain in optical resolution is on the order of 10³. It is shown that, based on this high resolution, one can study relaxation phenomena in polymers by the means of optical spectroscopy. Some simple relaxation phenomena are discussed together with some applications of narrow-band photochemistry in the field of high desity optical storage.     

Synthesis of two novel acenaphthyl-quinoxaline based low-band gap polymers and its electrochromic properties

Dispersion stability and electrokinetic properties of TiO₂ nanoparticles, dispersed in aqueous solution of polyallylamine hydrochloride (PAAm.HCl) and polyvinyl alcohol (PVA) blends was examined. The electrophoresis method was employed to study electrokinetic properties of nanodispersion by varying pH and temperature with an emphasis on dispersion stability. The measurements were performed over a wide range of pH from 2–12 and temperature from 25–65 °C and the isoelectric points (IEPs) of nanodispersions were determined. The concentration of TiO₂ was varied from 2–12 wt%. The dispersions were found to be quite stable (no sedimentation) over a period of two months. The zeta potential of nanodispersions decreases as the pH increases. When temperature increases, a more distinct decrease in the zeta potential was observed. Such behavior may be due to the changes occurring in the linear dimension of adsorbing macromolecules with increasing temperature. As temperatures increases, the adsorption of polymers causes a decrease in the diffuse layer charge, which leads to a decrease in zeta potential. Also, the increase in ionic strength leads to a compression of the diffuse layer and reduction in the zeta potential. The conductivity of nanodispersions increases for all pH and temperatures studied.     

Electrically conducting polymers from conjugated bis-phthalonitrile monomers

Elelectrically conducting polymers have been synthesized from completely conjugated bisphthalonitrile monomers. The monomers melt and are thermally polymerized at 260–300°C in air and then are converted into conductive materials by further processing at elevated temperatures in an inert atmosphere. Because the monomers remain in a liquid stage for 1–2 h, depending on the cure conditions, moldings, castings, and pre-pregs can be fabricated using conventional processing techniques. The conductivity can be varied from that of an insulator to approximately 10⁺²(Ωh cm)^?1. For example, after a 600°C treatment, the conductivity is approximately 1(Ω cm)^?1. Since reactive dopants are not used, the material and conductivity are stable in ambient as well as more aggressive environments, allowing them to function at 300°C and above. The monomers are well characterized, but the structure of the cured and postcured polymers are not yet well defined because of their high stability and intractability in the cured state.     

Some surface properties of plasma polymers prepared from hexamethyldisilazane and diethylaminotrimethylsilane

Plasma polymers from some silyl amines were produced by the radio frequency of 13.56 MHz, and the surface properties were investigated. The polymers were revealed to be as hydrophobic as a plasma polymer from tetramethylsilane, which does not contain nitrogen. The hydrophobicity became effective at around 50 Å thicknesses of these polymer layers deposited on micro-slide glass. These polymers have gradually become comparatively hydrophilic with the aging. The change of wettability is probably due to the oxidation of these surface layers to form oxides and peroxides, which are more hydrophilic. The hydrophobic character of silyl amine plasma polymers could be explained by the lack of amines and/or amides in these polymers, as observed with ATR-IR and ESCA spectra. These spectroscopic observations also suggest that nitrogen is a more fragile element in plasma than carbon or silicon in the silyl amines.     

Siloxane zwitterions: Synthesis and surface properties of crosslinked polymers

The aminoalkoxysilanes, γ-aminopropyltriethoxysilane and N-aminoethyl-γ-ainopropyl-trimethoxysilane, were chemically modified by ring-opening addition of γ-propanesultone. Surfaces coated with polymers from these new monomers have, at the surface, zwitterionic functions of sulfobetaines which are attached to the polymeric siloxane backbone. They showed good wettability, with critical surface tensions as high as 50 dynes/cm.     

Synthesis, characterization and electrochromic properties of a conducting copolymer of pyrrole functionalized polystyrene with pyrrole

A well-defined polystyrene (PSt) based polymer containing at one end-chain 3,5-dibromobenzene moiety, prepared by atom transfer radical polymerization (ATRP), was modified in two reaction steps. First one constitutes a Suzuki coupling reaction between aromatic dibromine functional polymer and 3-aminophenylboronic acid, when a diamino-containing intermediate was obtained. The second step is a condensation reaction between the diamino functional polystyrene and 2-pyrrole aldehyde. Thus, a polymer containing a conjugated sequence having pyrollyl groups at the extremities was synthesized. The presence of oxidable pyrrole groups in the structure of the polymer permitted further electropolymerization. The structures of intermediate polymers were analyzed by spectral methods (¹H NMR, FTIR). Electrochemical copolymerization of pyrrole functionalized polymer (PStPy) with pyrrole was carried out in acetonitrile (ACN)-tetrabutylammonium tetrafluoroborate (TBAFB) solvent electrolyte couple. Characterization of the resulting copolymer were performed via Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), spectroelectrochemical analysis, and kinetic study. Spectroelectrochemical analysis show that the copolymer of PStPy with Py has an electronic band gap (due to π-π* transition) of 2.4 eV at 393 nm, with a yellow color in the fully reduced form and a blue color in the fully oxidized form. Via kinetic studies, the optical contrast %ΔT was found to be 20% for P(PStPy-co-Py). Results showed that the time required to reach 95% of the ultimate T was 1.7 s for the P(PStPy-co-Py).     

电化学合成含交替苯/噻吩结构的电致变色聚合物

利用Kumada偶联合成了2,5-二苯基噻吩（DPT）、1,4-二噻吩基苯（DTP）及1,4-二（3-甲基-2-噻吩基）苯（DMTP）,并电聚合得到相应的聚合物PDPT、PDTP和PDMTP。PDPT的电化学稳定性较差,而PDTP和PDMTP在0～1.2 V间具有良好的电活性。此外,PDTP和PDMTP分别具有青-橙和红-绿-蓝的电致变色现象,可用于电致变色器件。     

Modifying and managing the surface properties of polymers

An ongoing challenge in polymer science is the preparation of materials with bespoke surface properties which differ from that of the bulk, for example hydrophobicity, wettability, chemical resistance, adhesion or biocompatibility. We highlight here recent efforts in the design, development and application of (multi)end‐functionalized polymers as additives for the efficient modification of polymer surface properties. Aryl‐ether moieties bearing up to eight functional groups have been used as initiators for the controlled polymerization of both styrene and methyl methacrylate by atom transfer radical polymerization (ATRP) and of lactide by ring opening polymerization (ROP). The resulting polymers have been used as additives to modify the surfaces of the corresponding bulk polymers. Fluorinated polymer surfaces are particularly appealing in terms of their liquid repellence, chemical inertness and low coefficient of friction. When an additive consisting of a low molecular weight polystyrene chain, end‐capped with four C₈F₁₇ groups, is present in a matrix of polystyrene at levels as low as 0.1%, near polytetrafluoroethylene‐like surface properties result. Copyright © 2007 Society of Chemical Industry     

Chelating polymers derived from polyvinyl alcohol and cellulose

Hydrophilic chelating polymers have been prepared by the reaction of organic compounds containing both a reactive halogen and a chelating function, with cellulose and, more especially, polyvinyl alcohol or their alkali metal derivatives. Suitable organic compounds used to illustrate the general reaction included: 5-chloromethyl-8-hydroxyquinoline, 5-chloro-8-hydroxyquinoline, ethyl γ-chloroacetoacetate and chloromethyl-kojic acid. Subsequent reaction of the kojic acid-polyvinyl alcohol polymer with diazotised o-arsanilic acid to give a polymer containing the azo-phenylarsonic acid group indicates further scope for these materials. Preliminary tests have shown that the polymers remove metal ions from aqueous solutions. Degradation occurred, however, when the polymers were regenerated with acids to elute adsorbed metal ions.     

Review study of electrochemical impedance spectroscopy and equivalent electrical circuits of conducting polymers on carbon surfaces

Electrochemical impedance spectroscopy (EIS) is an experimental method for characterizing electrochemical systems. This method measures the impedance of the concerned electrochemical system over a range of frequencies, and therefore the frequency response of the system is determined, including the energy storage and dissipation properties. The aim of this article is to review articles focusing on electrochemical impedance spectroscopic studies and equivalent electrical circuits of conducting polymers, such as polypyrrole, polycarbazole, polyaniline, polythiophene and their derivatives, on carbon surfaces. First, the conducting polymers are introduced. Second, the electrochemical impedance spectroscopic method is explained. Third, the results of EIS applications using equivalent electrical circuits for conducting polymers taken from the literature are reviewed.     

Synthesis and characterization of polymers derived from selenophene

The synthesis of poly(2,5‐selenophen‐oxo‐1,4‐phenylen‐selenide‐1,4‐phenylene‐oxo) (I) and poly(2,5‐selenophen‐oxo‐1,4‐phenylen‐diselenide‐1,4‐phenylen‐oxo) (II) by reaction of 2,5‐bis(1,4‐bromo‐phenylen‐oxo‐)‐selenophene with sodium selenide or diselenide, respectively, using dimethylformamide as solvent, is described. Both monomers and polymers were characterized by elemental analysis, melting point, and FTIR spectroscopy. Polymers I and II were doped with iodine and SbF₅ and characterized by SEM and XPS. Also, the conductivity and the T_g values were determined. For both polymers the best doping agent was iodine, although polymer II always presented higher conductivity, reaching values of about 6 · 10^?9 S · cm^?1. The T_g values suggest a likely crosslinking of the chains in polymer II when doped with SbF₅. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2019–2026, 2001     

Optical anisotropy and non-linear optical properties of azobenzene methacrylic polymers

Photoinduced optical anisotropy has been studied in several methacrylic copolymers, either amorphous or liquid crystalline, with cyano azobenzene chromophores in the side chain. Illumination with linearly polarised 488 nm light gives rise to high and stable values of birefringence and dichroism, mainly in liquid crystalline films. Both dichroism and birefringence decrease with the azo content in the copolymer series while some increase can be achieved by the incorporation of biphenyl molecules to the copolymers. Photoinduced anisotropy disappears above the glass transition temperature in amorphous polymers, whereas it increases in liquid crystalline polymers (LCP) due to a thermotropic self-organisation.The non-linear optical (NLO) properties of the films have been studied by second harmonic generation (SHG) measurements. The intensity of the harmonic signal from in situ corona poled polymeric films has been measured. The effect of 488 nm light irradiation on the azo chromophores orientation and consequently on the NLO response of the films was investigated at different temperatures. The intensity and thermal stability of the second harmonic signals obtained after the two different (thermal and photoassisted) corona poling processes have been compared.     

Sulfonium polymers derived from Ar-vinylbenzyl chloride. I. Exploratory study of the preparation and properties of the monomers and polymers

Although sulfonium salts are well known, polymeric sulfonium salts seldom have been mentioned in the chemical literature. This paper describes exploratory work in the preparation of various sulfonium monomers and polymers from ar-vinylbenzyl chlorides (ortho and para isomers). These chlorides—particularly the para isomer—reacted readily with 2,2′-thiodiethanol and water to yield the corresponding ar-vinylbenzyl sulfonium chloride monomers in aqueous solution. The odorless, reactive monomer mixture polymerized readily with persulfate or hydroperoxide catalysts; however, polymerization could be inhibited with cupric salts. Copolymerization with trimethyl(ar-vinylbenzyl)ammonium chloride was random. In copolymerization with acrylamide or acrylonitrile, the sulfonium monomer was more reactive. Analogous sulfonium monomers were made by reaction of ar-vinylbenzyl chlorides with various sulfides. In general, all the sulfonium monomers yielded homopolymers which were fairly stable in aqueous solution in the absence of strongly nucleophilic agents which would attack the sulfonium groups. However, when dried at room temperature the polymers would crosslink; and when heated, the polymers became hydrophobic also. Scrambling of the sulfonium group substituents during drying, and nucleophilic displacement reactions by chloride ion during heating were likely explanations. The high cationic charge on the polymers made them substantive to cellulose fibers. This property, when coupled with high nucleophilic reactivity of the sulfonium groups with the carboxylate sites of the pulp or other anionic counterious during drying and heating, made the polymers very effective as beater additives for imparting wet strength to paper.     

Composite nanofibers of conducting polymers and hydrophobic insulating polymers: Preparation and sensing applications

Various conducting polymer/hydrophobic insulating polymer (CP/HIP) composite nanofibers have been prepared by electrospinning and vapor deposition polymerization (VDP) with benzoyl peroxide (BPO) as oxidant. BPO is soluble in N,N-dimethylformamide (DMF) and can form homogenous solutions with hydrophobic polymers such as poly(methyl methacrylate) (PMMA) and polystyrene (PS). High-quality nanofibers of PMMA or PS containing a certain amount of BPO were produced by electrospinning and used as the templates for VDP of pyrrole, 3,4-ethylenedioxythiophene (EDOT), and aniline. The non-woven mats of the resulting CP/HIP composite fibers can be used as the high-sensitive sensing elements of gas sensors. A gas senor based on polypyrrole (PPy)/PMMA composite fibers was fabricated for sensing ammonia or chloroform vapor, and exhibited greatly improved performances comparing with those of the device based on a PPy flat film.     

Characteristic properties of cutting fluid additives derived from the derivatives of ricinoleic acid polymers

A number of esters were prepared from the reaction of acid chlorides with ricinoleic acid polymers and screened for anti-rust properties and antimicrobial activity in spent coolants of water-based cutting fluids. Aqueous solutions of triethanolamine salts with decanoic acid, undecanoic acid and oleic acid esters of ricinoleic acid dimer, trimer, tetramer and hexamer showed good anti-rust properties for water-based cutting fluids. Dehydrates of ricinoleic acid polymers also showed good anti-rust properties for water-based cutting fluids.     

Insight into high areal capacitances of low apparent surface area carbons derived from nitrogen-rich polymers

The energy storage mechanism of N-doped carbons with low apparent specific surface areas (Brunauer–Emmett–Teller specific surface area determined by N₂ adsorption) has puzzled the researchers in the supercapacitor field in recent years. In order to explore this scientific problem, such carbon materials were prepared through pyrolysis of N-rich polymers such as melamine formaldehyde resin and polyaniline. Although these carbons possess low apparent specific surface areas of no more than 60 m² g⁻¹, their areal capacitance could reach up to an abnormally high value of 252 μF cm⁻². The results of systematical materials characterizations and electrochemical measurements show that these carbons contain numerous ultramicropores which could not be detected by the adsorbate of N₂ but are accessible to CO₂ and electrolyte ions. These ultramicropores play dominant roles in the charge storage process for these low apparent surface area carbons, leading to an energy storage mechanism of electric double layer capacitance. The contribution of pseudocapacitance to the total capacitance is calculated to be less than 15%. This finding challenges the widely accepted viewpoint that the high capacitance of N-doped carbon is mainly attributed to the pseudocapacitance generated from the faradic reactions between nitrogen functionalities and electrolyte.     

Ionically conducting networks derived from PEO containing aziridine groups

Aziridine‐modified poly(ethylene oxide)s (PEOs) were obtained via 1,3‐dipolar addition of α,ω‐unsaturated PEO onto 3,3′‐diazidodiphenyl sulfone. The unsaturated telechelic functions used were allyl and methacrylate. To establish the structure of the condensation products, unsaturated model compounds of low molecular weight were also reacted with the same azide. The formation of a mixture of aziridine and triazoline functionalized compounds was proved when the unsaturation was of allylic type. Only aziridine function was detected in the case of methacrylate‐type unsaturation. The polymers containing aziridine functions were crosslinked by cationic ring opening polymerization of the aziridine units. The introduction of nitrogen‐containing heterocycles into the poly(ethylene oxide) backbone and their transformation into amine bridges induced an increase of the glass transition temperature (Tg) of the modified linear and crosslinked polymers as compared to the unmodified PEOs. Reciprocal Tg was shown to increase linearly when lithium trifluoromethanesulfone imide was introduced into the networks. Conductivity measurements were carried out and a maximum ionic conductivity of 6.10⁻⁶Scm⁻¹ at O/Li = 20 at room temperature was achieved. © 1999 Society of Chemical Industry     

Influence of side chains on electrochromic properties of green donor–acceptor–donor polymers

Three solution processable cathodically coloring green electrochromic polymers, based on 2,3-diphenyl-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, have been synthesized by oxidative FeCl₃ polymerization. The polymers were designed with solubilizing alkyl and oligoethylene oxide side chains to achieve solubility and processability. All three polymers have a small electrochemical bandgap (1.8–1.9 eV) and low oxidation potentials. Spectroelectrochemical studies of polymer films on ITO reveal that the alkyl side chains in head-to-head position on the polymer backbone promote a defined high-energy absorption peak and suppress tailing of charge-carrier absorption into the visible region. Kinetic studies, based on transmission measurements applying a square-wave potential between reduced and oxidized states, show that the polymer with exclusively oligoethylene oxide side chains (P3) had the fastest response times, monitored at the low-energy absorption maxima. The best performing polymer (P1) showed a good optical contrast in the visible region with a ΔT of 26% at 700 nm. An initial test of the electrochemical stability showed that the oligoethylene oxide containing polymers had superior stability over 500 full switches.     

Double layer capacitance of high surface area carbon nanospheres derived from resorcinol–formaldehyde polymers

Micro-mesoporous bimodal carbon nanospheres with high surface areas were synthesized by a combined use of surfactant templating technique and BaO₂ chemical activation one. Starting spherical nanopolymer/surfactant composites were prepared by the NaOH-catalyzed reaction of resorcinol (R) and formaldehyde (F) in the presence of cetyltrimethylammonium bromide (CTAB) as a core template and 1,3,5-trimethylbenzene (TMB) and tert-butanol (t-BuOH) as cosurfactants. After pretreatment with hydrochloric acid, the composite materials were calcined at 1000 °C in N₂ coexistent with varying weight ratios of BaO₂ to RF polymer ranging from 0 to 11. It produced micro-mesoporous bimodal carbon nanospheres of 124–143 nm diameter, with specific surface areas as high as 1884 m² g⁻¹ or up to 3301 m² g⁻¹, in contrast to microporous ones with smaller surface areas obtained at low BaO₂-loadings. The electrochemical double layer capacitance of the resulting nanocarbons in 0.5 M H₂SO₄ showed a marked increase with specific surface areas, up to as high as 219 F g⁻¹ for the highest surface area carbon material.     

含辣素衍生结构疏水缔合聚合物的制备及性能

为了改进聚丙烯酰胺在原油三次采收领域存在的耐温耐盐性能差等问题，采用无助溶剂的无皂乳液聚合方式，以微量（0.05mol%）辣素衍生单体N-[3-（丙烯酰氨基甲基）-2-羟基-4,5-二甲基苄基]-丙烯酰胺（HMMAM）为功能性单体，与甲基丙烯酸十八烷基酯（SMA）、甲基丙烯酸异冰片酯（IBOMA）等共聚合成新型疏水缔合聚合物PACSAM和PACIAM以提高聚丙烯酰胺的各项耐受性能。采用FTIR、1HNMR、TGA、SEM等进行结构和形貌表征；探讨聚合物的疏水缔合特性、耐温耐盐性、溶解性及缓蚀性能等。结果表明，PACIAM和PACSAM存在稳定的三维网状结构，临界缔合浓度分别为4.5 × 10-3 g/mL和4 × 10-3 g/mL，微量辣素衍生单体的引入使0.01 g/mL聚合物溶液在30℃下表观黏度提升至776 mPa·s和1224 mPa·s，90 ℃黏度保留率为37.57%和41.44%，在0.01 g/mL的NaCl溶液中黏度保留率为37.57%和42.12%，溶解速率为25 min和27 min，4 × 10-3 g/mL的聚合物溶液的缓蚀效率可达96.76%和97.28%，表明微量HMMAM的引入大大增加了聚合物的各项性能。