Preparation and thermal properties of asymmetrically substituted poly(silylenemethylene)s

Poly(silylenemethylene)s of the types [SiMeRCH₂]_n and [SiHRCH₂]_n were prepared by the ring-opening polymerization (ROP) of 1,3-disilacyclobutanes (DSCBs) containing n-alkyl substituents, such as C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, and n-C₆H₁₃, or a phenyl group on the Si. These new polymers include a monosilicon analog of poly(styrene), [SiHPhCH₂]_n. Improved synthesis routes to the DSCB monomers were developed which proceed through Grignard ring closure reactions on alkoxy-substituted chlorocarbosilanes. All of these asymmetrically substituted polymers were obtained in high molecular weight form, except for [SiHPhCH₂]_n. The configurations of all of the polymers were found to be atactic. The aryl-substituted polymers have higher glass transition temperatures (T_gs) and thermal stability than those of the alkyl-substituted poly(silylenemethylene)s. Unlike the polyolefins of the type [C(H)(R)CH₂]_n, where T_g drops continuously from R = Me to n-Hex, the T_gs of the n-C_nH_2n+1 (n = 2–6)-substituted [SiMeRCH₂]_n PSM's appear to reach a maximum (at −61°C) for the R = n-Pr-substituted polymer. Moreover, where it was possible to make direct comparisons among similarly substituted atactic polymers, all of the poly(silylenemethylene)s were found to have lower T_gs than their all-carbon analogs. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3193–3205, 1997     

Phase behavior of a substituted poly(paraphenylene): Poly(para-2,5-didecyl-p-phenylene)

The thermal behavior of poly(para-2,5-didecyl-p-phenylene) has been investigated by differential scanning calorimetry and real time X-ray diffraction. Poly(para-2,5-didecyl-p-phenylene) is a semicrystalline material that crystallizes in a layered structure. The system exhibits two thermal transitions in the investigated temperature range. The first one, occurring at lower temperatures, provokes a reduction of the layered spacing accompanied by an appreciable disordering of the lateral side chains. Above the first transition the material is shearable, highly viscous, and birefringent. Thus, we have associated this transition to the formation of a layered mesophase. The higher temperature transition exhibits a twofold endothermic DSC peak and is characterized by the disappearance of X-ray diffracted intensity. At temperatures above the second transition the system presents the characteristics of an isotropic melt. Consequently, we have associated this transition with the complete disordering of the polymeric backbones. By following an appropriate thermal treatment it has been shown that the twofold shape of the endotherm characterizing the higher temperature transition can be changed into a single endotherm. This effect has been interpreted as being due to the kinetics of main-chain ordering. This ordering seems to proceed by the initial growth of domains with a high level of order followed by the subsequent increase of these domains through the inclusion of less ordered material. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 49–54, 1998     

Chemical and electrochemical doping in poly(paraphenylene vinylene) blends

Blends of poly(p-phenylene vinylene) (PPV), with other polymers were made by film-casting from an aqueous mixture of the water-soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F₅, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free-standing PPV/PEO blend samples as rechargeable battery electrodes.     

Determination of amino- and carboxyl end-groups in poly(paraphenylene terephthalamide)

Summary Two chemical methods are described for the quantitative determination of amino- and carboxyl end-groups in poly(paraphenylene terephthalamide). The amino end-groups are determined by heterogeneous reaction with 1-fluoro-2,4-dinitrobenzene. After washing out the excess of reagent, the modified polymer is dissolved in methanesulphonic acid and the introduced dinitrophenyl group is measured spectrophotometrically. The determination of carboxyl endgroups is based on a quantitative conversion to an amino group, nitrogen and carbon dioxide with sodium azide in 100 % sulphuric acid. The liberated carbon dioxide is determined by potentiometric titration. The standard deviations of the methods are 2.5 mmole COOH/kg and 0.7 mmole NH₂/kg within the range of 5–200 mmole/kg.

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Bestimmung von Amino- und Carboxylendgruppen in Poly(paraphenylen-terephthalamid)

Zusammenfassung Zwei chemische Methoden, die eine quantitative Bestimmung der Amino- und Carboxylendgruppen in Poly(paraphenylen-terephthalamid) ermöglichen, werden beschrieben. Die Aminoendgruppen werden durch eine heterogene Reaktion mit 1-Fluor-2,4-dinitrobenzol bestimmt. Nach Auswaschen des Reagensüberschusses wird das modifizierte Polymer in Methansulfonsäure gelöst und die eingeführte Dinitrophenylgruppe spektrophotometrisch gemessen. Die Bestimmung der Carboxylendgruppen basiert auf einer quantitativen Umsetzung zu einer Aminogruppe, Stickstoff und Kohlendioxid mit Natriumazid in 100 %iger Schwefelsäure. Das freigesetzte Kohlendioxid wird durch potentiometrische Titration bestimmt. Die Standardabweichungen der Methoden betragen 2,5 mmol COOH/kg und 0,7 mmol NH₂/kg im Bereich von 5–200 mmol/kg.

     

Voltammetric and waveguide spectroelectrochemical characterization of ultrathin poly(aniline)/poly(acrylic acid) films self-assembled on indium-tin oxide

We report on the spectroelectrochemical characterization of conducting polymer (CP) films, composed of alternating layers of poly(aniline) (PANI) and poly(acrylic acid) (PAA), deposited on ITO-coated, planar glass substrates using layer-by-layer self-assembly. Absorbance changes associated with voltammetrically induced redox changes in ultrathin films composed of only two bilayers (ITO/PANI/PAA/PANI/PAA) were monitored in real time using a unique multiple reflection, broadband attenuated total reflection (ATR) spectrometer. CP films in contact with pH 7 buffer undergo a single oxidation/reduction process, with ca. 12.5% of the aniline centers in the film being oxidized and reduced. The ATR spectra indicate that during an anodic sweep, the leucoemeraldine form of PANI in these films is oxidized to generate both the emeraldine and pernigraniline forms simultaneously. A comparison of the behavior observed during anodic and cathodic sweeps suggests that the rate of oxidation is limited by structural changes in the polymer film originating in electrostatic repulsion between positively charged PANI chains.     

Layer-by-layer self-assembled ultrathin multilayer films of lanthanide polyoxometalates and poly(allylamine hydrochloride) and their photoluminescent properties

Ultrathin multilayer films of two lanthanide polyoxometalates (LPOMs), K(17)[Eu(P(2)W(17)O(61))(2)] (EPW) and K(13)[Eu(SiW(11)O(39))(2)] (ESW), and poly(allylamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. UV-vis spectroscopy and ellipsometry respectively show that the absorbance values at characteristic wavelengths and the thicknesses of the multilayer films increase linearly with the number of LPOM/PAH bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. Average thicknesses of ca. 3.4 and 2.4 nm were determined for the EPW/PAH and ESW/PAH bilayers by ellipsometry, respectively. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide the surface morphology of the LPOM/PAH films, indicating that the film surface is relatively uniform and smooth. The photoluminescent properties of these films have also been investigated by fluorescence spectroscopy. The LPOM/PAH multilayer film has a good thermal stability as shown by UV-vis, X-ray photoelectron, and fluorescence spectra.     

Time–temperature-dependent behavior of a substituted poly(paraphenylene): Tensile,creep, and dynamic mechanical properties in the glassy state

The linear viscoelastic behavior of a poly(paraphenylene) with a benzoyl substituent has been examined using tensile, dynamic mechanical, and creep experiments. This amorphous polymer was shown to have a tensile modulus of 1–1.5 Msi, nearly twice that of most common engineering thermoplastics. The relaxation behavior, which is similar to that of common thermoplastics, can be described by the WLF equation. Outstanding creep resistance was observed at low temperatures, with rubbery-like behavior being exhibited as the temperature approached T_g. Physical aging was shown to interact with long-term creep, rendering time–temperature superposition invalid for predicting the long-term properties. The effect of physical aging on the creep behavior was characterized by the shift rate μ. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 70: 2971–2979, 1998     

Infrared spectra of asymmetrically substituted tetraphenylporphyrins

The Z and D isomers of 2-methoxycarbonylvinyl-5,10,15,2D-tetraphenylporphyrin and their copper and zinc complexes have been investigated by means of ID spectroscopy. It has been shown that when the electron-acceptor methoxycarbonylvinyl group is substituted into the -pyrrole position of the porphyrin ring, the character of conjugation between the -electron systems of the porphyrin macrocycle and the phenyl rings remain substantially unchanged. Also, there is no appreciable conjugation of the electron clouds of the tetraphenylporphyrin molecule and the methoxycarbonylvinyl. A series of infrared absorption bands has been registered for isomers of the tetraphenylporphyrin derivatives that were investigated. It has been found that the frequencies of three metal-sensitive bands of the IR spectra will vary depending on the nature of the cental metal ion; the electronic nature of such behavior of these bands is examined.Institute of Biophysics, Moscow. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 108–114, January–February, 1991. Original article submitted September 13, 1988.     

Characterization and tribological investigation of self-assembled trimethoxysilyl-functionalized poly(phthalazinone ether ketone)thin films on glass substrates

<正>Trimethoxysilyl-functionalized PPEK(PKGS) films had been designed to serve as wear resistant coatings for silicon surfaces. These surface films were formed by a dip-coating technique applied to self-assembled monolayers(SAMs).The formation and wetting behavior of PKGS films were characterized by means of contact angle measurement.The friction coefficient of the film prepared is very low(about 0.1),and the anti-wear behavior is good,with a lack of failure after sliding over 1800 s.     

Trapping of charge carriers in colloidal particles of self-assembled films from TiO(2) and poly(vinyl sulfonic acid)

Self-assembled electrodes consisting of TiO(2) nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared by the layer-by-layer (LbL) technique. The electrostatic interaction between the TiO(2) nanoparticles and PVS allowed the growth of visually uniform multilayers of the composite, with high control of the thickness and nanoarchitecture. The electrochemical and chromogenic properties of these TiO(2)/PVS films were examined in an electrolytic solution of 0.5 M LiClO(4)/propylene carbonate. The presence of two intercalation sites was noted during the positive potential scan, and they were attributed to different mobilities of charge carriers. Several charge/discharge cycles demonstrated the trapping of charge carriers in the TiO(2) sites. The absorbance change associated with the oxidation of the trapping sites was attributed to electronic transitions involving energy states in the gap band formed due to the strong distortion of the TiO(2) host. Using the quadratic logistic equation (QLE), it was possible to analyze the electronic intervalence transfer from Ti(3+) to Ti(4+). Using the parameters obtained from this fitting, the amount of trapping sites in the LbL film was also determined. Electrochemical impedance spectroscopy (EIS) data gave the time constant associated with diffusion and the trapping sites. The diffusion coefficient of lithium ions changed from ca. 4.5 x 10(-13) cm(2) s(-1) to 3.0 x 10(-14) cm(2) s(-1) for all the potential range applied, indicating that PVS did not hinder the ionic transport within the LbL film. Finally, on the basis of the spectroelectrochemical data and scanning electron micrographs, the trapping effects were attributed to the colloidal particles of Li(0.55)TiO(2).     

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3683–3688, 1997     

Solid-phase synthesis of asymmetrically branched sequence-defined poly/oligo(amidoamines)

We present for the first time the synthesis of asymmetrically branched sequence-defined poly/oligo(amidoamines) (PAAs) using solid-phase synthesis with the capability of introducing diversity at the side chains. We introduce two new versatile (diethylenetriamine) building blocks for solid-phase synthesis bearing Fmoc/Boc and Fmoc/Alloc protecting groups expanding recently used Fmoc/Boc protecting group strategy for linear PAAs to an Fmoc/Alloc/Boc strategy. This allows for orthogonal on-resin cleavage of Fmoc and Alloc protecting groups during solid-phase synthesis of PAAs with backbones differing in chain length and sequence. With these structures we then demonstrate the potential for generating asymmetrical branching by automated multiple on-resin cleavage of Alloc protecting groups as well as the introduction of side chains varying in length and number. Such systems have high potential as nonviral vectors for gene delivery and will allow for more detailed studies on the correlation between the degree of branching of PAAs and their resulting biological properties.     

Structural studies of poly(paraphenylene), poly(2,5-thienylene) and their derivatives by solid-state NMR of 1H and 13C

Transient techniques in NMR of ¹H and ¹³C were used to study the chemical and physical structures of solid poly(p-phenylene) (PPP), poly(2,6-dimethyl-p-phenylene oxide) (PDMPO), poly(p-phenylene sulfide) (PPS), poly(p-biphenylene sulfide) (PPBS), poly(p-phenylene selenide) (PPSe), poly(p-biphenylene selenide) (PPBSe), poly(2,5-thienylene) (PT), poly(3-methyl-2,5-thienylene) (PMT), and poly(p-phenylene-co-2,5-thienlyene) (PPPT) of different monomer ratios. ¹³C NMR confirmed the expected chemical structure for homopolymers, and indicated a random distribution of monomer units in PPPT. Relative fractions of crystalline and interfacial regions were determined by measurements of ¹H magnetic relaxation, ¹³C CP/MAS NMR, and XRD. © 1994 John Wiley & Sons, Inc.     

Directed growth of poly(isobenzofuran) films by chemical vapor deposition on patterned self-assembled monolayers as templates

This paper describes a method to direct the formation of microstructures of poly(isobenzofuran) (PIBF) by chemical vapor deposition (CVD) on chemically patterned, reactive, self-assembled monolayers (SAMs) prepared on gold substrates. We examined the growth dependence of PIBF by deposition onto several different SAMs each presenting different surface functional groups, including a carboxylic acid, a phenol, an alcohol, an amine, and a methyl group. Interferometry, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), and optical microscopy were used to characterize the PIBF films grown on the various SAMs. Based on the kinetic and the spectroscopic analyses, we suggest that the growth of PIBF is surface-dependent and may follow a cationic polymerization mechanism. Using the cationic polymerization mechanism of PIBF growth, we also prepared patterned SAMs of 11-mercapto-1-undecanol (MUO) or 11-mercaptoundecanoic acid (MUA) by microcontact printing (microCP) on gold substrates as templates, to direct the growth of the PIBF. The directed growth and the formation of microstructures of PIBF with lateral dimensions of 6 microm were investigated using atomic force microscopy (AFM). The average thickness of the microstructures of PIBF films grown on the MUO and the MUA patterns were 400 +/- 40 nm and 490 +/- 40 nm, respectively. SAMs patterned with carboxylic acid salts (Cu2+, Fe2+, or Ag+) derived from MUA led to increases in the average thickness of the microstructures of PIBF by 10%, 12%, or 27%, respectively, relative to that of control templates. The growth dependence of PIBF on the various carboxylic acid salts was also investigated using experimental observations of the growth kinetics and XPS analyses of the relative amount of metal ions present on the template surfaces.     

Regiodefined substituted poly(2,5-thienylene)s

The polymerization of 3,3″-dialkylterthiophenes overcomes the lack of regiospecificity associated (to some extent) with all the polymerization methods in use, thus allowing the preparation of perfectly regioregular polymers endowed with enhanced electrical and optical properties. Moreover, the larger spacing of the alkyl chains achieved with the insertion of an unsubstituted thiophene unit confers to such regioregular polymers an extraordinary doping stability. Two regiochemically defined alkoxy-substituted terthiophenes were also polymerized and the effects of the effects of the presence and position of the alkoxy group on the polymerization reaction and on the polymer properties are discussed. © 1993 John Wiley & Sons, Inc.     

Synthesis and thermal behavior of poly(ethylene oxide) poly(N‐substituted urethane)

Poly(N‐substituted urethane)s with an alkyl or ligo(ethylene oxide) monomethyl ether side chain were synthesized by the reaction operating in the following two‐step process: first, by metalation of the starting polymer with potassium tertiary butoxide (t‐BuOK) and then by treatment of the obtained urethane polyanion with tosylate in dimethyl sulfoxide. The thermal properties of poly(ethylene oxide) poly(N‐substituted urethane) (N‐sub PEOPU) were investigated in view of the N‐substitution degree and properties of the substituent. The chemical structures were characterized by Fourier transform infrared, ¹H NMR, and ¹³C NMR spectroscopies. DSC and thermogravimetric analysis (TGA) were used to investigate the thermal properties of N‐sub PEOPUs. As the degree of N‐methylation increased, the glass‐transition temperature (T_g) of the N‐sub PEOPUs linearly decreased from 6 to ?29 °C, and the weight‐loss temperature of 5% (T) from TGA in air increased from 278 to 360 °C. In the fully N‐substituted PEOPUs, the behavior of the thermal decomposition of the PEOPU that was processed in two stages was changed to one‐step decomposition in the temperature range of 360–440 °C. The T_g was shifted to a lower temperature with an increasing length of the substituent in N‐sub PEOPU. Improvement of the thermal stability by N‐substitution was more significant in N‐alkyl PEOPU than in N‐ethoxylate PEOPU. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4129–4138, 2001     

Counterions in poly(allylamine hydrochloride) and poly(styrene sulfonate) layer-by-layer films

The amount of counterions in layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) has been determined with X-ray photoelectron spectroscopy (XPS) for films prepared from solutions with various NaCl concentrations. Sodium and chloride counterions are present in LBL films produced from salt solutions, which are located at the surface and in the bulk of the films. The percentage of bulk counterions increases with the ionic strength of the polyelectrolyte before reaching a constant value. The bulk sodium/sulfur percentage ratios tend to 0.8 for samples washed with pure water and for samples washed with NaCl aqueous solutions, while the bulk chlorine/nitrogen percentage ratios tend to 0.5 for the same samples. The ratio between the percentages of polyelectrolyte ionic groups lies close to unity for all samples, indicating that counterions do not contribute to charge compensation in the polyelectrolyte during the adsorption process. The presence of counterions in LBL films is explained by Manning condensation near the polyelectrolyte ionic groups, leading to inter-polyelectrolyte ionic bondings via ionic networks. It is believed that condensation leads to the formation of NaCl crystallites in these LBL films, which was confirmed by X-ray diffraction measurements.