Polymers containing formamidine groups

Summary New aromatic polymers containing formamidine groups were prepared by high temperature solution polycondensation of triethyl orthoformate with various aromatic diamines. The resulting polyformamidines were characterized by elemental analysis, IR' and ¹H NMR spectroscopy, viscosity measurements, thermogravimetry, DSC- and WAXS measurements. With few exceptions aromatic polyformamidines show excellent solubility in polar solvents and strong acids, but they were gradually decomposed in extended contact with moisture. Polyformamidines containing rigid para structures are well crystallizing materials, which was proved by WAXS investigations. Glass transition temperatures in the range of 62 – 163°C were observed for semicrystalline or amorphous polymers. All aromatic polyformamidines are thermally stable in nitrogen up to 300°C.     

Influence of Temperature on the Properties of Polycarbosilane

A polycarbosilane precursor of SiC fiber was synthesized at high temperature under high pressure from liquid polysilane (LPS), which was obtained by thermal decomposition of poly(dimethylsilane). The effect of reaction temperature on the Si–H bond content, degree of linearity, Si–Si bond content, molecular weight, molecular weight distribution, elemental composition, softening point, and yield of the polycarbosilane (PCS) was studied spectroscopically (FTIR, UV, ¹H-NMR, and ²⁹Si-NMR) and by gel permeation chromatography (GPC). The results showed that the molecular weight, yield and softening point of the PCS increased, the molecular weight distribution broadened, and the Si–Si bond content and degree of linearity decreased when the reaction temperature increased. The Si–H bond content increased when the thermolysis reaction temperature was less than 450°C and decreased when the temperature was over 460°C. Increasing of the reaction temperature affected the composition with a general decrease in the amount of carbon, hydrogen and oxygen in the product. A middle molecular weight region of PCS in the GPC appears when the reaction temperature approaches 450°C; and, the as-synthesized PCS was stable with low Si–Si bond content. Synthetically, the conversion process is initially the formation of PCS by thermal decomposition of LPS, which is followed by an increase in molecular weight via condensation of PCS molecules.     

Synthesis and Characterization of Polyaspartimides Containing Anisyl Moiety

New class of aromatic bismaleimides containing anisyl group were synthesized from bis(4-amino 3,5-dimethyl phenyl) anisyl methane and maleic anhydride via bismaleamic acid as an intermediate followed by cyclodehydration to bismaleimides. The structure was confirmed by FTIR, ¹H-NMR and elemental analysis. Further, a series of polyaspartimides were synthesized by addition reaction of bismaleimide (BMDA) with various diamines. The polymers were characterized by IR and elemental analysis. The polymers exhibit good solubility in organic solvents such as NMP, DMF and DMSO. They exhibit good thermal stability. T _g of polyaspartimides are in the range of 125–278°C and T _10% weight loss are in the range of 398–476°C.     

Living cationic polymerization of isobutyl vinyl ether initiated by the trimethylsilyl iodide/zinc iodide system

Summary Trimethylsilyl iodide in conjunction with zinc iodide (Me₃SiI/ZnI₂) as an initiating system led to living cationic polymerization of isobutyl vinyl ether in toluene at 0 or –40°C or in methylene chloride at –40°C (ZnI₂ was dissolved in acetone). The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit trimethylsilyl iodide. At room temperature (+25°C), however, the polymerization failed to give perfectly living polymers; the polymer molecular weight was smaller than the calculated value. On addition of a fresh feed of monomer at the end of the polymerization at –40°C, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight continued to increase in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (M_w/M_n< 1.1).Living cationic polymerization of vinyl ethers by electrophile/Lewis acid initiating systems, part 2. For part 1 see ref. 2     

Synthesis and properties of new sulfonated poly(p-phenylene) derivatives for proton exchange membranes. I

Several high molecular weight poly(2,5-benzophenone) derivatives were synthesized by high yield nickel-catalyzed coupling polymerization of 2,5-dichloro-4′-substituted benzophenones. The monomers were prepared by Friedel-Crafts catalyzed reaction of 2,5-dichlorobenzoyl chloride and several aromatic compounds. The resulting polymers are organosoluble and show no evidence of crystallinity by differential scanning calorimetry (DSC). The temperatures of 5% weight loss of the polymers via dynamic thermogravimetric analysis in air were above 480 °C. Sulfonation of selected polymers utilizing concentrated or fuming sulfuric acid at room temperature introduced sulfonic acid moieties to the aromatic side group. Activated fluoro aryl groups were also used to generate pendent sulfonated functionalities. The sulfonated polymers were examined for ion exchange capacities, water absorption capacities and proton conductivities. The sulfonated polymers were not good film formers, but could be demonstrated to show high values of proton conductivity in the range of 0.06-0.11 S/cm when supported on glass fabrics or via polymer blending strategies.     

Syntheses and Properties of Metal Containing Polyimides Based on the Gold Carbene Complex

A novel gold carbene complex, bis(1,3-di-p-dimethylaminobenzylimidazolidinylidene) gold(I), was synthesized and polymerized to polyimides in a one-step method with various aromatic dianhyrides. The gold-coordinated polyimides are characterized by IR and NMR (¹H, ¹³C) spectroscopy. The materials have inherent viscosities that range from 1.88 to 2.39 dl/g and show excellent solubility in N-methylpyrrolidone and N,N-dimethylacetamide. The glass transition temperatures of the coordinated polyimides range from 203–265°C and a 5% weight loss in air is observed from 535–578°C. The polymers form dark yellow, tough films that are transparent above 365 nm. The effect of different flexible units on the properties of the polyimides is discussed.     

Partial oxidation of methane to syngas over Co/MgO catalysts. Is it low temperature?

Co/MgO catalysts with high Co-loading (>28 wt%) are able to initiate the reaction of methane with oxygen at temperatures around 500 °C. High conversions of methane ( 70%) and very high selectivities for hydrogen and carbon monoxide ( 90%) are obtained at very high reactant gas space velocities (10⁵–10⁶ h^–1). The temperature of the catalyst at the conditions of partial oxidation of methane to form syngas was found to be extremely high (1200–1300 °C); it is about 600–850 °C higher than that previously reported by others. At these temperatures, high temperature homogeneous reactions may prevail. It is suggested that combustion of methane to carbon dioxide occurs on the catalyst with major heat release and that methane and water, respectively methane and carbon dioxide are reformed thermally in an endothermic reaction leading to syngas.     

Reactivity in radical polymerization ofN-substituted maleimides and thermal stability of the resulting polymers

Summary The effect ofN-substituents on the radical polymerization ofN-substituted maleimides (RMI) was investigated. The polymerization reactivities, i.e. yield and molecular weight of the polymers, were found to change depending on the structure of theN-substituents. The poly(RMI)s bearing a bulkyN-substituent were confirmed to be semiflexible poly(substituted methylene)s which were soluble in many organic solvents, but did not melt below their decomposition temperatures. From thermogravimetric analysis determined in a nitrogen stream, no weight-loss of poly(RMI) was observed at temperature below 300°C, and the maximum decomposition temperature was 400–440°C, except forN-tert-alkyl substituted derivatives which decomposed at 240–280°C via a two-step reaction.     

Ring-Opening Polymerization of Siloxanes Using Phosphazene Base Catalysts

Phosphazene bases such as {(NMe₂)₃P=N–)₃P=NBu^t} have been reported in the literature to be strongly basic materials with basicities up to 1×10¹⁸ times stronger than that of diazabicycloundecene (DBU) a strong hindered amine base used in organic reactions. A study of these phosphazene bases as catalysts revealed that they can be activated by small amounts of water, which all silicone feed stocks contain, to form an active ionic base catalyst [(NMe₂)₃P=N–)₃P–NHBu^t]⁺[OH]^–. This paper discusses the use of these types of base catalysts, and their analogues, as ring-opening polymerization catalysts for cyclosiloxanes. Phosphazene base catalysts can be used at low concentrations to make high molecular weight polydimethylsiloxanes with short reaction times over a wide temperature range. Molecular weight can easily be controlled in the presence of suitably functionalized endblockers. Water and carbon dioxide have been shown to have a significant impact on the polymerization rates. Polymers prepared show excellent thermal stability by thermogravimetric analysis (TGA), following neutralization of the catalyst, with decomposition onset temperatures >500°C in some cases. As a result of the extremely low levels of catalyst used, the polymers often do not require filtration.     

Organoiron Polyelectrolytes: Synthesis and Characterization of Cationic Cyclopentadienyliron Complexes of Polyarylether-Imines

The synthesis of an aromatic ether complex of cyclopentadienyliron containing two terminal aldehyde groups was achieved via metal-mediated nucleophilic aromatic substitution reactions. This dialdehyde monomer was subsequently reacted with a variety of aliphatic and aromatic diamines to produce the corresponding soluble cationic organoiron polyether-imines. These cationic organometallic polymers were characterized using IR, ¹H, and ¹³C NMR, viscosity and thermogravimetric analysis. Viscosity measurements showed that these polymers exhibited polyelectrolyte effects in DMSO solutions. Thermogravimetric analysis showed that decoordination of the iron moieties occurred at about 300°C for polymers with aliphatic spacers in their backbones, while the cyclopentadienyliron moieties were cleaved from the polymers with aromatic spacers in their backbones at about 200°C. Photolytic demetallation of the organoiron polymers resulted in the removal of the pendent cyclopentadienyliron moieties and allowed for the isolation of their organic analogs. While the organoiron polymers were soluble in polar organic solvents, the corresponding organic polymers exhibited very limited solubilities or were insoluble. The organic polymers had glass transition temperatures between 101 and 120°C     

Effects of cobalt, temperature and certain impurities upon cobalt electrowinning from sulfate solutions

The effects of cobalt concentration, temperature and the presence of zinc, copper and iron ions in the electrolyte on current efficiency and cathodic quality were investigated by cyclic voltammetry and galvanostatic methods during cobalt electrowinning. The results showed that high cathodic efficiency of cobalt deposition was obtained from solutions containing cobalt concentration in the range 30–60 g l^–1. Current efficiency increased from 94% to 97% with increase in cobalt concentration to 60 g l^–1 at 20 °C. It was also found that increase in temperature to 50 °C enhanced the cobalt deposition reaction, along with the rate of hydrogen evolution, resulting in little change in current efficiency. The presence of foreign cations in the electrolyte not only adversely affects current efficiency but also promotes cracking and peeling.     

Synthesis and photochromic behavior of new polyimides containing azobenzene side groups

Aromatic polyimides containing side azobenzene groups have been synthesized by low-temperature solution polycondensation of certain aromatic dianhydrides with aromatic diamines containing preformed side azobenzene groups followed by chemical imidization at 100 °C in the presence of pyridine and acetic anhydride. The weight average molecular weight of these polymers is in the range of 16,000-129,000. The glass transition temperature of these polyimides is in the range of 185-230 °C. The polymer architecture presents a special characteristic, one of the azobenzene aromatic units being in the main chain of the polymer. This situation is intermediary between main-chain and side-chain azobenzene-containing polymers. The photochromic behavior, determined by the trans-cis isomerization process of azo-groups, in solution and in solid state, was evaluated. The synthesized polyimides were studied by spectral methods (UV, IR), thermal analysis and molecular modeling. A preliminary study concerning the surface structuration capacity of the polyimides was accomplished. Good results were obtained using Nd:YAG laser at 355 nm, at an incident fluence of 35 mJ/cm² (situated below the laser ablation limit).     

Preparation and properties of polyamide-imides derived from 1,3-bis(4-aminophenoxy)benzene,trimellitic anhydride,and various aromatic diamines

A diamine, 1,3-bis(4-aminophenoxy) benzene (II), was synthesized in two steps; fist from the condensation of resorcinol with p-chloronitrobenzene in the presence of potassium carbonate, producing I ,3-bis(4-nitrophenoxy) benzene (I), followed by hydrazine hydrate/Pd-C reduction. A two imide rings-preformed dicarboxylic acid, 1,3-bis(4-trimellitimidophenoxy)benzene (III), was prepared from the condensation of diamine II and trimellitic anhydride in 1:2 molar ratio. A series of structurally new polyamide-imides (V_a-p) were directly synthesized from the diacid III and various aromatic diamines (IV_a-p). The resultant polyamide-imides had inherent viscosities between 0.56–1.39 dl/g. All polymers, except some derived from diamines with p-phenoxy structure, showed excellent solubility. Some polymer resulted in tough or flexible transparent films. Dynamic TG data indicated that all polymers possess excellent thermal stability with no significant weight loss up to the temperature of approximately 450 °C in nitrogen, and their 10% weight loss temperature was recorded in the range of 489–577 °C. Measurements of wide-angle X-ray diffraction revealed that some polymers derived from p-phenoxy group-containing diamines showed crystalline patterns.     

Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution Part III: A Fourier transformed infrared spectroscopy study

FTIR spectroscopy was employed to investigate high molecular weight substances formed on a platinum electrode surface during the electrochemical oxidation of phenol and its chlorinated derivatives. Potentiodynamic (potential range from –0.80 V to 0.85 V vs SHE; scan rate 200 mV s^–1) and potentiostatic (at 0.78 V vs SHE) electropolymerization was used in alkaline solutions (1 M NaOH) containing 0.1 M of phenol, monochlorophenols, dichlorophenols, trichlorophenols and pentachlorophenol. The IR spectra of the corresponding monomers were recorded for the comparison. The FTIR spectroscopy studies revealed that the polymers formed under potentiodynamic and potentiostatic conditions are of aromatic nature (–C=C– stretching vibrations at 1450–1600 cm^–1), they have ether-linkages (=C—O—C= stretching vibrations at 1100–1300 cm^–1) and quinone groups (–C=O stretching vibrations at 1630–1800 cm^–1 and –C—H out-of-plane bending at 760 cm^–1). The intensities of the hydroxyl group bands in most of the polymers are rather weak compared to those in the corresponding monomers. Vibrations at 2850–2960 cm^–1, which are present in most of the IR spectra of polymers formed under cyclic voltammetry conditions, correspond to the stretching vibrations of the sp³ hybridized C—H bond and suggest that the cleavage of the benzene ring occurs to some extent during electrooxidation–electropolymerization of phenol and its chlorinated derivatives when reaching the potential of oxygen evolution (0.85 V vs SHE).     

Preparation and properties of poly(amideether-imide)s derived from 1,4-bis(4-aminophenoxy)benzene,trimellitic anhydride,and various aromatic diamines

An imide ring containing dicarboxylic acid, 1,4-bis(4-trimellitimidophenoxy)benzene (III), was prepared by the condensation of 1,4-bis(4-aminophenoxy)benzene and trimellitic anhydride. A series of new poly(amide-ether-imide)s were prepared by the direct polycondensation of diimide-diacid III with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents inN-methyl-2-pyrrolidone (NMP) in the presence of calcium chloride. The highest inherent viscosity value of a poly(amide-ether-imide) obtained was 1.78 dL/g (inN,N-dimethylacetamide, DMAc, at 30 °C). Flexible films with excellent tensile properties were cast from DMAc solutions. Glass transition temperatures of these poly(amide-ether-imide)s were recorded in the range of 248–297 C. These polymers do not show obvious weight loss before 400°C; the decomposition temperatures at which 10% weight loss in nitrogen and in air were observed for these poly(amide-ether-imide)s in the range of 521–564°C and 501–539°C, respectively. The polymers derived fromp-phenylenediamine or the diamines containing 1,4-bisphenoxy units exhibited a higher degree of crystallinity and higher initial decomposition temperatures but poor solubility in organic solvents.     

Polymers containing formamidine groups

Summary Aliphatic polyformamidines have been synthesized by reaction of aliphatic diamines with triethyl orthoformate in presence of catalytic amounts of acetic acid. The reaction has been carried out in DMSO at 180°C. The polymer structure has been confirmed by IR and NMR spectroscopy. For determination of molecular weights ¹H NMR end group signals have been used.     

In situ high temperature FTIR studies of NOx reduction with propylene over Cu/ZSM-5 catalysts

High temperature in situ FTIR has been used to investigate the surface species present on Cu/ZSM-5 during the reduction of NO_x with propylene in a lean environment. Parallels have been observed between adsorbed surface species and catalytic activity for this reaction. Species detected at low temperatures are not representative of those detected at high temperatures where the catalyst is active. An oxidized nitrogen-containing species has been observed at 2580 cm^–1 on Cu during reaction conditions (400°C). In contrast, at low temperatures, where the catalyst is less active, coke and Cu⁺-CO predominated. The effects of Cu weight loading, C/NO ratio, reaction temperature, and catalyst deactivation by steaming have been investigated with IR.     

Thermal battery cells utilizing molten nitrates as the electrolyte and oxidizer

The Ca/LiNO₃-LiCl-KCl (50-25-25 mol%) thermal battery cell can be activated at 160° C and operated over a temperature range of 250–450° C to produce 2.5–2.8 V at open-circuit and initial operating voltages above 2 V at 10 mA cm^–2. At operating temperatures between 250 and 350° C, this system shows promise for applications requiring a sixty-minute thermal battery. Cell lifetimes decrease at higher temperatures due to the accelerating reaction of calcium with the molten nitrate salt to form gaseous products. An experimental energy density value of 142 Whkg^–1 was obtained at 300° C during constant current discharge at 10 mAcm^–2. Effects of applied face pressure on cell discharge characteristics were small. At current densities above 20–30 mA cm^–2, the cell performance deteriorates due to polarization at the anode. This is probably caused by the precipitation of CaO which blocks the active sites at the anode.     

Comparative evaluation of the thermal properties of aromatic fibres (polyoxazole,polyimide, and polyaramid)

The thermal properties of the aromatic fibres Arselon, Arselon-C, Arimid, and Armos, as-spun and heat-treated are investigated using methods of thermomechanical and dynamic thermogravimetric analysis and differential scanning calorimetry. According to the TMA data, Arselon, Arselon-C, Arimid, and heat-treated Armos fibres retain size stability up to 400°C. Shrinkage is no more than 1–2%. As-spun Armos fibres lengthen insignificantly (under 7%). The temperature characteristics of aromatic fibres obtained by TGA and DSC show that thermooxidative degradation markedly begins at temperature above 390–400°C.Translated from Khimicheskie Volokna, No. 5, pp. 45–48, September–October, 2004.     

Sintering and recrystallization of high-purity magnesia-alumina spinel during hot pressing

Conclusions A study was made of the densification and recrystallization of magnesia — alumina spinel of high dispersion during hot pressing in the temperature range 1200–1600°C, a pressure of 60–300 cm², and a holding time of 10–30 min.The relative density of 92–98% theoretical was achieved at 1300–1400°C, a pressure of 300 kg/cm², and a soaking of 10 min. The spinel of theoretical density with a finely crystalline homogeneous structure was obtained by hot pressing at 1450–1600°C.Intensive recrystallization of the spinels during hot pressing occurs in the temperature range ensuring maximum rate of densification (1450–1600°C).The rate of recrystallization of the spinel grains during hot pressing at 1400°C and a pressure of 300 kg/cm² and soakings of 10 and 30 min, has the order of 10^–6 cm/sec and the maximum for the grains of diameter from 2 to 6.Report read at a symposium on pure oxide sintering, Khar'kov, 1968.Deceased.Translated from Ogneupory, No.6, pp. 32–36, June, 1970.