Conformational properties of aromatic polyesters of terephthalic acid

Hydrodynamic (sedimentation, diffusion and viscometry) and optical [flow birefringence (FB)] properties of solutions of p-aromatic copolyesters obtained by the polycondensation of three components

with various molar ratios of N, D and T, have been investigated. Independent methods of quantitative evaluation of the parameter of equilibrium rigidity, the length of the statistical Kuhn segment, for the most rigid of copolymers soluble in tetrachloroethane with the molar ratio of components N:D:T = 0.7:0.3:1 gave the values of A = 160·10^?10 m (translational friction) and 180·10^?10 m (FB). The equilibrium chain rigidity of an insoluble p-aromatic polyester containing no D component, ensuring chain flexibility and polymer solubility, was evaluated from the dependence of birefringence on copolymer composition. The value of the statistical Kuhn segment obtained in this case A = (500–800)·10^?10m is close to that for the most rigid aromatic polyamide-poly-p-benzamide.     

Synthesis, characterization and constitutional isomerism study of new aromatic polyamides containing pendant groups based on asymmetrically substituted meta-phenylene diamines

Four new aromatic polyamides containing pendant groups were synthesized by low temperature interfacial polycondensation of two asymmetrically substituted diamine monomers, namely, 4-[4-(1-methyl-1-phenylethyl) phenoxy]-1,3-diamino benzene and 4-{4-[(4-methylphenyl) sulphonyl]phenoxy}-1,3-diamino benzene with two aromatic diacid chlorides, namely isophthaloyl chloride and terephthaloyl chloride. Inherent viscosities of polyamides were in the range 0.64-0.72 dL/g indicating formation of medium molecular weight polymers. The weight average molecular weights and number average molecular weights, determined by gel permeation chromatography (polystyrene standard), were in the range 54,500-65,000 and 19,750-27,000, respectively. The constitutional isomerism of synthesized polyamides was investigated by ¹H and ¹³C NMR spectroscopy, where as the constitutional order was calculated from ¹H NMR spectroscopy and was found to be in the range 0.35-0.37. Polyamides containing pendant groups were essentially amorphous and were soluble in polar aprotic solvents such as N, N-dimethyl acetamide, N-methyl-2-pyrrolidone, N, N-dimethyl formamide and dimethyl sulfoxide. Polyamides exhibited glass-transition temperature in the range 237-254 °C. The initial decomposition temperature, determined by TGA in nitrogen atmosphere, of polyamides was in the range 371-410 °C indicating their good thermal stability.     

A novel stir bar sorptive extraction coating based on monolithic material for apolar, polar organic compounds and heavy metal ions

In this study, a novel stir bar sorptive extraction (SBSE) based on monolithic material (SBSEM) was prepared. The monolithic material was obtained by in situ copolymerization of vinylpyrrolidone and divinylbenzene in the presence of a porogen solvent containing cyclohexanol and 1-dodecanol with azobisisobutyronitrile as initiator. The influences of polymerization conditions on the extraction efficiencies were investigated, using phenol and p-nitrophenol as detected solutes. The monolithic material was characterized by various techniques, such as elemental analysis, scanning electron microscopy, mercury intrusion porosimetry, infrared spectroscopy. Polycyclic aromatic hydrocarbons were used to investigate the extraction efficiencies of SBSEM for apolar analytes. Hormones, aromatic amines and phenols were selected as test analytes to investigate the extraction efficiencies of SBSEM for weakly and strongly polar compounds. The results showed that the new SBSEM could enrich the above-mentioned organic compounds effectively. It is worthy to mention that the SBSEM can enrich some heavy metal ions, such as Cu²⁺, Pb²⁺, Cr³⁺ and Cd²⁺, through coordination adsorption. To our best knowledge, that is the first to use SBSE to enrich heavy metal ions.     

Ceria supported Ru~0-Ru~(δ+) clusters as efficient catalyst for arenes hydrogenation

Selective hydrogenation of aromatic amines,especially chemicals such as aniline and bis(4-aminocyclohexyl)methane for non-yellowing polyurethane,is of particular interests due to the extensive applications.To conquer the existing difficulties,in selective hydrogenation,,the Ru~0-Ru~(δ+)/CeO_2 catalyst with solid frustrated Lewis pairs was developed for aromatic amines hydrogenation with excellent activity and selectivity under relative milder conditions.The morphology,electronic and chemical properties,especially the Ru~O-Ru~(δ+) clusters and reducible ceria were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),sca nning electronic microscopy(SEM),X-ray photoelectron sp ectroscopy(XPS),CO_2 tempe rature programmed deso rption(CO_2-TPD),H_2 tempe rature programmed reduction(H_2-TPR),H_2 diffuse reflectance Fourier transform infrared spectroscopy(H_2-DRIFT),Raman,etc.The 2% Ru/CeO_2 catalyst exhibited good conversion of 95% and selectivity greater than 99% toward cyclohexylamine.The volcano curve describing the activity and Ru state was found.Owning to the "acidic site isolation" by surrounding alkaline sites,condensation between the neighboring amine molecules could be effectively suppressed.The catalyst also showed good stability and applicability for other aromatic amines and heteroarenes containing different functional groups.     

Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

A series of difunctional fluorene-based benzoxazine monomers were synthesized from the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with formaldehyde and primary amines including aniline, o-toluidine, n-butylamine, and n-octylamine. Their chemical structures were confirmed by FT-IR, ¹H and ¹³C NMR analyses. The curing behaviors of the precursors were monitored by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polymers were evaluated with DSC and thermogravimetric analysis (TGA). The fluorene-based polybenzoxazines show the typical curing characteristic of oxazine ring-opening for difunctional benzoxazines centred at 231-250 °C, and remarkably higher glass transition temperature and better thermal stability ascribed to the high rigidity, high aromatic content, and intermolecular and intramolecular hydrogen bonding. The thermal decomposition temperature and char yield of aromatic amine-fluorene-based polybenzoxazines are much higher than those of aliphatic amine-based polybenzoxazines.     

Radiation chemical studies of protein reactions: Effect of irradiation liquid containing aromatic hydrocarbons and pH on viscosity

When protein is irradiated by γ-rays from a ⁶⁰Co source in various liquids containing aromatic hydrocarbons, such as benzene, naphthalene, and phenanthrene, the effect of the radiation varies with the irradiation liquids containing aromatic hydrocarbons. An empirical equation for the viscosity change was obtained. Protein irradiated by γ-rays from a ⁶⁰Co source in air showed the effect of pH on protein reactions. An empirical equation for the viscosity change was obtained.     

Excess enthalpies of some aromatic aldehydes in n-hexane, n-heptane and benzene

Calorimetric measurements of molar excess enthalpies, H^E, at 298.15 K, of mixtures containing aromatic aldehydes of general formula C₆H₅(CH₂)_mCHO (with m = 0, 1 and 2) + n-hexane, n-heptane or benzene are reported, together with the values of H^E at equimolar composition compared with the corresponding values of H^E for the aromatic ketones in the same solvents. The experimental results clearly indicate that the intermolecular interactions between the carbonyl groups (CHO) are influenced by the intramolecular interactions between the carbonyl and phenyl groups, particularly for the mixtures containing benzaldehyde.     

Flow birefringence and conformational characteristics of polyamide hydrazide molecules in dimethylsulphoxide

Flow birefringence (FB) and intrinsic viscosity of 19 samples of aromatic polyamide hydrazide (PAH) in dimethylsulphoxide (DMS), previously characterized by their weight-average molecular weights by the light scattering method, have been investigated. The molecular-weight dependence of reduced birefringence according to theory [12] was used to determine the optical anisotropy of a monomer unit Δa = (200 ± 20) 10^?25cm³ and the length of the Kuhn segment $\text{A = (250 ± 30)}\text{A}\text{?}$ of PAH molecules. The second independent evaluation of rigidity of the PAH chain $\text{A = (240 ± 30)}\text{A}\text{?}$ was obtained according to the theory of rotational friction of rigid wormlike chains by using the coefficients of rotational diffusion of PAH molecules determined from the characteristic values of orientation angles of FB. The value of rigidity of the PAH chain obtained by this method is in good agreement with the data on molecular dimensions obtained by light scattering.     

Proton-exchange membrane electrolytes derived from phosphonic acid containing poly(arylene ether)s

A novel phosphonic acid containing bisphenol was successfully synthesized from phenolphthalein and m-aminophenylphosphonic acid. Poly(arylene ether)s containing phosphonic acid groups were prepared from the bisphenol. This is the first report on the attachment of phenylphosphonic acid groups as side chains to aromatic polyethers. These polyethers had very high glass transition temperatures and molecular weights. The conductivities of the polyethers ranged from 10⁻⁵ to 10⁻⁶ S cm⁻¹ and therefore show promise as proton-exchange polymer electrolyte membranes for fuel cells.     

Hydrodynamic and conformational properties of silicon-substituted addition-type polynorbornene macromolecules

Seven polynorbornene samples containing trimethylsilyl side groups that were prepared by the addition polymerization of 5-trimethylsilyl-2-norbornene in the presence of catalytic systems (π-C₅H₉NiCl)₂-methylaluminoxane and nickel naphthenate-methylaluminoxane have been studied by translational isothermal diffusion and viscometry. The molecular masses of the polymer samples are measured. Kuhn-Mark-Houwink equations for diffusion coefficient D and intrinsic viscosity [η] are determined in toluene at 25°C: D = 6.94 × 10^?4 M ^?0.61 and [η] = 1.53 × 10^?3 M ^0.82. The equilibrium rigidity of polymers chains is estimated as A = 47 ± 9 Å. The conformational features of the silicon-containing polynorbornene are analyzed by the PM3 quantumchemical semiempirical method on the basis of simulation of its decamer chain fragments. In terms of microstructure and equilibrium rigidity, the above-described addition poly(trimethylsilylnorbornene) is close to poly(trimethylsilylpropyne) synthesized using niobium pentachloride as a catalyst. This finding explains similar membrane gas-separation properties of these polymers.     

Aromatic polyamides with pendent acetoxybenzamide groups and thin films made therefrom

New aromatic polyamides containing 1,3,4-oxadiazole or benzonitrile units in the main chain and 5-(4-acetoxybenzamido) groups in the side chain have been synthesized and their properties have been characterized and compared with those of related polyamides and polyoxadiazole-amides. These polymers show good thermal stability, with initial decomposition temperature being at about 300 °C and glass transition temperature in the range of 260-280 °C. They are easily soluble in certain solvents such as N-methylpyrrolidinone (NMP), N,N^′-dimethylacetamide (DMA) and N,N^′-dimethylformamide (DMF) and can be cast from solutions into thin flexible films. The polymer films had tensile strengths in the range of 77-97 MPa, tensile moduli in the range of 2.3-2.6 GPa and elongation at break values ranging from 6% to 24%. One of the polymers containing the 1,3,4-oxadiazole ring exhibited blue fluorescence.     

Nitroaldol-reaction of aldehydes in the presence of non-activated Mg:Al 2:1 hydrotalcite; a possible new mechanism for the formation of 2-aryl-1,3-dinitropropanes

Commercially available, non-activated 2:1 Mg:Al hydrotalcite catalyzes the nitroaldol reaction between a variety of aromatic and aliphatic aldehydes and simple nitroalkanes such as nitromethane and nitroethane. A new mechanism is proposed for the formation of the 1,3-dinitropropanes. The threo/erythro diastereoselectivity of the nitroethane-adducts was determined by ¹H NMR spectroscopy and was found to range from 50:50 to 70:30. The substituents of the aromatic aldehydes influenced the isomer ratio.     

Synthesis and properties of polyimides derived from a new diamine containing bulky-flexible pendent group

Novel aromatic polyimides containing bulky-flexible pendent group were successfully synthesized by direct polycondensation of N-(4-(4-(4,5-diphenyl-1H-imidazole-2-yl)phenoxy)phenyl)-3,5-diaminobenzamide with various tetracarboxylic dianhydrides. These polymers are soluble in most of the aprotic organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethylsulfoxide, N,N-dimethylacetamide, hexamethylphosphoramide, m-cresol, and pyridine. The prepared polymers were characterized by viscometry, FT-IR, ¹H NMR, and UV-Vis spectroscopy, fluorimetry, elemental analysis; the thermal properties were evaluated by differential scanning calorimetric and thermogravimetric analysis.     

Energy transfer from cis- and trans-decalin to benzene and toluene in their irradiated mixtures

The fluorescence from β^- particle irradiation of cis- and trans-decalin containing benzene or toluene has been studied as a function of aromatic concentration from ⋍ 0.002 to 0.1 M and over a spectral range that encompasses both the solvent and aromatic fluorescence. By comparisons with the fluorescence obtained using sub-ionization excitation of the decalin, the effect of benzene and toluene to intrude into the geminate ion-pair decay process has been extracted and rate constants for their scavenging action obtained via fitting to the standard diffusion model. The rate constants are compared to those reported from microwave conductivity studies on the “escaped” mobile hole in these liquids. For the reaction between trans-decalin⁺ + toluene, the rates are in good agreement. However, for the reactions of either cis- or trans-decalin⁺ with benzene, the rate constants extracted from the fluorescence analysis are about an order of magnitude larger. The discrepancies suggest the existence of differences in the internal energies and structures of the decalin positive ions when observed on the very short time scale of geminate recombination (probed in the fluorescence measurements) and that which is observed on the much longer time scales that are probed in the microwave experiments.An analysis of the development of aromatic fluorescence permits extraction of the fraction of aromatic fluorescence that derives from ionic recombination (as opposed to energy transfer) and the averaged efficiency of this recombination. In all of the systems studied here the ionic fraction remains high (i.e. >;20%) even at millimolar concentrations of the aromatic.     

Radiation Chemical Studies of Protein Reactions: Effect of Irradiation Liquids Containing Aromatic Hydrocarbons and pH on the Breaking of Secondary Bonding in Protein

When protein in various liquids containing aromatic hydrocarbons, such as benzene, naphthalene, and phenanthrene, is irradiated by γ-rays from a ⁶⁰Co source, the breaking of secondary bonding in the protein molecule varies with the irradiation liquids containing aromatic hydrocarbons. Protein irradiated by γ-rays from a ⁶⁰Co source in air showed the effect of pH on the breaking of secondary bonding in the protein molecule. In both cases an empirical equation for the viscosity change was obtained, and the phenomena were explained on the basis of the molecular mechanism.     

Synthesis and properties of thermally stable and optically active novel wholly aromatic polyesters containing a chiral pendent group

5-(2-Phthalimidyl-3-methyl butanoylamino)isophthalic acid (5), as a novel diacid monomer containing phthalimide and flexible chiral groups, was prepared by the reaction of 2-phthalimidyl-3-methyl butyric acid chloride (4) with 5-aminoisophthalic acid (5AIPA) in dry N,N-dimethylacetamide (DMAc). A series of novel polyesters (PE)s containing phthalimide group was prepared by the reaction of diacid monomer 5 with several aromatic diols via direct polyesterification with the tosyl chloride/pyridine/dimethylformamide (DMF) system as a condensing agent. The resulting new polymers were obtained in good yields with inherent viscosities ranging between 0.37 and 0.61 dL g⁻¹ and were characterized with FT-IR, ¹H NMR, elemental and thermogravimetric analysis techniques. These polymers are readily soluble in amide type solvents such as DMAc, DMF, 1-methyl-2-pyrrolidone, hexamethyl triaminophosphine, dimethyl sulfoxide and protic solvents such as sulfuric acid. Thermogravimetric analysis showed that the 10% weight loss temperature in a nitrogen atmosphere was more than 345 °C, which indicates that the resulting PEs have a good thermal stability as well as excellent solubility.     

Effect of isocyanate structure on deblocking and cure reaction of N-methylaniline-blocked diisocyanates and polyisocyanates

Two series of N-methylaniline-blocked isocyanates based on monomeric diisocyanates such as 4,4′-methylene bis(phenyl isocyanate), toluene-2,4-diisocyanate, isophorone diisocyanate and 1,6-diisocyanato hexane and their NCO terminated polyurethane prepolymer (polyisocyanates) were prepared and characterized thoroughly by FTIR, ¹H NMR, ¹³C NMR and EI-Mass spectroscopic methods. The blocking reaction of N-methylaniline with aromatic isocyanates and aromatic polyisocyanates occur faster when compared to the aliphatic isocyanates. The deblocking reactions of blocked isocyanates were carried out under dynamic and isothermal conditions using hot-stage FTIR spectrophotometer. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate kinetics and thermodynamics parameters. Cure reactions of blocked isocyanates with hydroxyl-terminated polybutadiene were also followed to establish the structure-property relationship of the N-methylaniline-blocked isocyanates. The deblocking studies of blocked isocyanates reveal that the aromatic isocyanates undergo deblocking easily compared to aliphatic isocyanates. The rate of deblocking reaction of N-methylaniline-blocked aromatic polyisocyanates was found to be higher compared to N-methylaniline-blocked aromatic monomeric diisocyanate adducts. On the other hand, this trend was just reverse in the cure-reaction studies. The dissolution behavior of N-methylaniline-blocked isocyanates in Terathane-2000, polypropylene glycol-2000, polycaprolactone diol-2000 and hydroxyl-terminated polybutadiene-2500 was also studied and found that all adducts are soluble in these polyols.     

Correlation between physical properties and conformational rigidity of some aromatic polyimides having pendant phenolic groups

Soluble polyimides based on an aromatic diamine containing pendant phenolic group and four different dianhydrides have been synthesized by two-step polycondensation reaction in solution. The polyimides were easily soluble in polar organic solvents and even in less polar solvents and showed high thermal stability, with initial decomposition temperature being above 420 °C. Monte Carlo method was used to calculate conformational rigidity parameters of these polyimides. Some physical properties such as solubility, glass transition temperature and initial decomposition temperature were investigated and compared with those of related polyimides which did not contain any pendant groups based on the same dianhydrides and a diamine without pendant phenolic group. All data were discussed in relation to the rigidity of the chain.

     

Quaternary Chiral β2,2‐Amino Acids with Pyridinium and Imidazolium Substituents

The reactions of cyclic sulfamidates as electrophiles with a variety of nitrogen‐containing aromatic heterocycle nucleophiles, such as pyridines, N‐alkylimidazoles and N‐methylbenzimidazol, was explored. In all cases, although the nucleophilic substitution reactions occurred on quaternary centres, elimination products were not detected. The inversion of configuration at this quaternary centre was determined by X‐ray diffraction analysis and the enantiomeric excess of the reactions was checked by chiral HPLC. This synthetic approach allowed us to obtain a new family of chiral charged β^2,2‐amino acids, including a new bisamino acid that incorporates an imidazolium salt as a cross‐linker. In this context, the treatment of these chiral imidazolium salts with Ag₂O opens the way to new chiral N‐heterocyclic carbenes, which are important substrates in the fields of organometallic and organocatalytic chemistry. Additionally, we have done a thorough conformational analysis of these β‐amino acid derivatives, both in the solid state and in solution. The most important conformational feature of these acyclic systems is the rigidity of the N‐CH₂‐C‐N⁺ dihedral angle, which is essentially due to the gauche effect.     

Pyrimidine based carboxylic acid terminated aromatic and semiaromatic hyperbranched polyamide-esters: synthesis and characterization

Carboxylic acid terminated aromatic and semiaromatic hyperbranched polyamide-esters (HBPAEs) containing pyrimidine moieties were prepared by polycondensation of 4-hydroxy-2,6-diaminopyrimidine (CBB′) to a double molar ratio of various diacid chlorides (A₂) without any catalyst. The products were soluble in organic solvents, such as N,N-dimethylformamide, N-methyl-2-pyrrolidone and displayed glass transition temperature (T_g) between 180 and 244 °C. The polymerization products have been investigated with FTIR, ¹H and ¹³C NMR analyses and the degree of branching was higher than 60%. Amorphous polymers had inherent viscosity (η_inh) ranging between 0.21-0.28 dL/g and had excellent thermal stability with 10% weight loss at 346-508 °C.