Heat capacity and thermodynamic functions of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl

The heat capacity (C _{p m} ) of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl in the temperature range of 8—373 K was measured by low-temperat ure adiabatic calorimetry, and thermodynamic characteristics of the solid-phase transitions of 4,4′-d i-tert-butylbiphenyl were determined. Temperatures, enthalpies, entropies of melting, and the purity of the samples of the tested substances were determined by means of differential scanning calorimetry. The main thermodynamic functions of the substances in the condensed state at 298 K were calculated.     

Syntheses and Crystal Structures of 4,4′Diformyl-diphenoxyethane and 4,4′4′′-Triformyl-triphenoxytriethylamine

1 INTRODUCTION With the methods of [2+3] and [1+1] tripodal condensation of polyaldehyde with polyamine, many Schiff bases and their relative reduced polyaza cryptands have been facilely synthesized in high yields[1～5]. In this one-step route, some metal ions such as alkali[2, 6, 7], alkali earth[8], rare earth[9, 10] and other transition ions[4, 11, 12] were used as templates[13, 14]. Formerly, the dialdehydes are needed to be rigid structures[15] to prevent themselves from polymeri…     

Investigation on structure and thermal behavior of 4,4′-dihydroxyazobenzene functionalized with epoxy groups

A new symmetric compound with azobenzene chromophore and epoxide groups, namely diglycidyl ether of 4,4′-dihydroxyazobenzene (DGEAB) was obtained and characterized. Its thermal behavior was monitored taking into account that many reactions of epoxides are carried out under heating. DGEAB was found to be stable up to 200 °C, but at higher temperature, its decomposition involves three step of degradation with the formation of an appreciable quantity of the char.     

Coordination behaviour and thermolysis of some rare-earth complexes with 4,4′-bipyridine and di- or trichloroacetates

A novel mixed-ligand complexes with empirical formulae: Dy(4-bpy)(CCl₂HCOO)₃ · H₂O and Ln(4-bpy)_1.5(CCl₃COO)₃ · 2H₂O (where Ln(III) = Ce, Nd) were prepared and characterized by chemical and elemental analysis and IR spectroscopy, conductivity (in methanol, dimethyloformamide and dimethylsulfoxide). Analysis of the diffractograms showed that the obtained complexes are crystalline. Way of metal-ligand coordination discussed. The thermal properties of complexes in the solid state were studied under non-isothermal conditions in air atmosphere. During heating the complexes decompose via intermediate products to the oxides: Ln₂O₃ (Nd, Dy) and CeO₂. TG-MS system was used to analyse principal volatile thermal decomposition and fragmentation products evolved during pyrolysis of Dy(4-bpy)(CCl₂HCOO)₃ · H₂O in air.     

A Convenient Synthesis of 4,4′-Dimethylaminodiphenyl Diselenide and 4,4′-Dinitrodiphenyl Diselenide

A simple, rapid and efficient synthesis of 4,4′-dimethylamino-diphenyl diselenide 1 and 4,4′-dinitrodiphenyl diselenide 2 is described. The method consists of the reductive cleavage of the Se-CN linkage in the corresponding aryl selenocyanates by sodium borohydride followed by air oxidation of the resulting seleno-lates. The diselenides 1 and 2 are readily obtained in a state of high purity, in 89 and 80% yield, respectively.     

Characterization and thermal kinetic studies on charge-transfer complexes of 4,4′-bipyridine with benzoquinone derivatives

4,4′-Bipyridine belong to an important class of compounds with wide applications in different fields and since the formation charge transfer compounds give opportunity to improve the physical and chemical properties of different donors so charge transfer compounds of 4,4′-bipyridine (Bpy) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone [chloranilic acid] (CHA) and 2,3,5,6-tetrachloro-1,4-benzoquinone [choloranil] (CHL) were studied. The stoichiometries of the reactions were determined from photometric titration methods. Although the thermodynamic parameters [Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy change (ΔS°)] were calculated. The thermal decomposition of the complexes follows first order kinetics and thermodynamic parameters of the decomposition were calculated. The structural morphology was investigated by scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM) and show that these molecules are of nanosize.     

Cluster structure of epoxy-phenolic polymer prepared by curing a mixture of epoxy-4,4′-isopropylidenediphenyl and phenol-formaldehyde oligomers

The kinetics of viscosity variation and the concentration and kinetic modes of precondensation of a mixture of epoxy-4,4-isopropylidenediphenyl and phenol-formaldehyde oligomers in Cellosolve solutions in the presence of phosphoric acid at 333 K were studied. The cluster structure parameters of the chemical network of epoxy-phenolic polymeric coating on a tin plate, obtained by thermal curing of precondensates of an oligomer mixture, were determined using the silver chloride sputtering method.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1382–1388.Original Russian Text Copyright © 2004 by Krasovskii, Novikov, Filippov.     

Reduction of 4,4′-Stilbenequinone and 4,4′-Diphenoquinone upon Reaction with Photogenerated Radicals

The properties of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone (StQ) were studied by photochemical means. Acetone, acetophenone or benzophenone was photolyzed in the presence of both StQ and a donor, such as alcohols or triethylamine. This initiated reaction of a ketyl radical with StQ to form a semiquinone radical and eventually induce a permanent bleaching due to conversion of StQ to 4,4′-dihydroxystilbene (StQH₂). The quantum yield of conversion of StQ to StQH₂ increases with the donor concentration. Similar effects were found for the ketone-sensitized radical-induced conversions of the analogous diphenoquinone to the reduction product, diphenol.     

Studies on the curing and thermal behaviour of diglycidyl ether of bisphenol-A (DGEBA) in the presence of aromatic diimide–diacids

This paper describes the synthesis and characterization of aromatic diimide–diacids (DIDAS) obtained by reacting pyromellitic dianhydride (PMDA), 4,4′-oxo diphthalic anhydride (ODA), 1,4,5,8-naphthalene tetra carboxylic dianhydride (NTDA) with excess of 4-aminobutyric acid (B) or 6-aminohexanoic acid (H) using N,N-dimethyl formamide (DMF) as solvent. The synthesized compounds were used as curing agents to investigate the effect of structure on the curing and thermal behaviour of diglycidyl ether of bisphenol-A (DGEBA). Structural characterization of DIDAS was done by using FTIR, ¹H-NMR, ¹³C-NMR spectroscopy and elemental analysis. Curing behaviour of DGEBA in the presence of aromatic DIDAS was investigated by differential scanning calorimetry (DSC). The peak exotherm temperature (T _P) was low in the case of DIDAS synthesized from ODA and high in the case of DIDAS synthesized from NTDA. Thermal stability of the isothermally cured DGEBA with DIDAS was investigated using dynamic thermogravimetry in nitrogen atmosphere. The char yield was highest for resin cured with DIDAS containing NTDA.     

Curing behavior of epoxy resins with a series of novel curing agents containing 4,4′-biphenyl and varying methylene units

A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (T _g) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (T _d) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the T _g and T _d of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.     

Effect of thermal curing on the properties of thin films based on benzophenonetetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyldiphenylmethane

The processing of polyimide films from polyamidic acid solutions involves the simultaeous loss of solvent and chemical conversion, and may imply structural reorganization such as orientation or crystallization. The effect of thermal treatment on the thermal, mechanical and dielectric properties of polymer films based on benzophenonetetracarboxylic dianhydride and 4,4’-diamino-3,3’-dimethyl diphenylmethane have been investigated. The thermal treatment of polyamidic acid at different temperatures led to compounds with different degree of imidization; it turned out that the imidization process took place with high speed until 240 °C and then remained constant. The dynamic mechanical analysis (DMA), contact angles, and dielectric measurements revealed that the storage modulus and contact angles increased with increasing of curing temperature while the dielectric constant decreased.     

Curing and thermal behaviour of diamide–diimide–diamines based on l-phenylalanine with epoxy blends containing phosphorus/silicon

A series of diamide?Cdiimide?Cdiamines (DADIDAs) were synthesized by reacting diacid N,N??-(3,3??,4,4??-benzophenone tetracarboxylic)-3,3??4,4?? diimido-bis-l-phenylalanine (I) with different aromatic diamines viz. 1,4-phenylene diamine (PD), 1,5-diamino naphthalene (N), 4,4??-(9-fluorenyllidene)-dianiline (F), 4,4??-diaminodiphenyl sulphide (DS) and 3,4??-oxydianiline (O). The diacid (I) was synthesized by the condensation of 3,3??,4,4??-benzophenone tetracarboxylic dianhydride (BTDA) with l-phenylalanine (PA) in a solution of glacial acetic acid and pyridine (3:2 v/v) at refluxing temperature. The resulting DADIDAs so synthesized were characterized with the help of elemental analysis (EA) and spectroscopic techniques, and were used as epoxy curing agents. Two epoxy blends (EP and ES) were prepared, each by mixing in an equivalent ratio of 2:3 of tris(glycidyloxy)phosphine oxide (TGPO) with diglycidyl ether of bisphenol-A (DGEBA) and 1,3-bis(3-glycidyloxypropyl)tetramethyl disiloxane (BGPTMSO) with diglycidyl ether of bisphenol-A (DGEBA), respectively. A series of new epoxy thermosets with good thermal stability were prepared by reacting EP/ES with synthesized DADIDAs stoichiometrically. Thermal properties of these epoxy resins were observed using the techniques viz. Differential scanning calorimeter (DSC) for curing behaviour and Thermogravimetric analysis (TGA) to study the thermal stability and mass loss behaviour. All the samples showed good thermal stabilities in terms of char yield (24.8?C52.7) and calculated LOI (27.4?C38.6), thereby demonstrate their effective use as flame retardant systems.     

Thermochemical studies of 4-tert-butylbiphenyl and 4,4′-di-tert-butylbiphenyl

The standard massic energies of compounds of 4-tert-butylbiphenyl and 4,4′-di-tert-butylbiphenyl were measured at T = 298.15 K by static-bomb combustion calorimetry. The standard enthalpies of vaporization, fusion and sublimation were measured in a Calvet microcalorimeter, or by differential scanning calorimetry. The standard molar enthalpies of formation in the condensed and gaseous states were obtained from these data. The tert-butyl group increments for the substitution of one hydrogen atom in a position “4” in biphenyl molecule were calculated.     

Structural, thermal, and spectral investigations of the lanthanide(III) biphenyl-4,4′-dicarboxylates

The lanthanide biphenyl-4,4′-dicarboxylates (bpdc) series of the general formulae Ln₂(bpdc)₃·nH₂O, where Ln = lanthanides from La(III) to Lu(III); bpdc = C₁₂H₅(COO) ₂ ^2? ; n = 4, 5 or 6 have been obtained by the conventional precipitation method. All prepared complexes were characterized by elemental analysis, simultaneous thermal analyses thermogravimetric-differential scanning calorimetry (TG–DSC) and TG–FT-IR, FT-IR, and FT-Raman spectroscopy as well as X-ray diffraction patterns measurements. In the whole series of analyzed complexes the bpdc^2? ligand is completely deprotonated. In view of that, four carboxylate oxygen atoms are engaged in the coordination of Ln(III) ions. The synthesized compounds are polycrystalline and insoluble in water. They crystallize in the low symmetry crystal systems, like monoclinic and triclinic. Heating in the air atmosphere resulted in the multi-steps decomposition process, namely endothermic dehydration and strong exothermic decomposition processes. The dehydration process leads to the formation of stable anhydrous Ln₂bpdc₃ compounds which subsequently decompose to the corresponding lanthanide oxides.     

Electrochemical and spectroscopic properties of poly-4,4′-dialkoxy-2,2′-bipyrroles

The structure and the electrochemical and spectral properties of two conductive electrochemically polymerized substituted bipyrroles 4,4′-methoxy-2,2′-bipyrrole and 4,4′-buthoxy-2,2′-bipyrrole were studied and compared. The polymers were characterized by cyclic voltammetry, FT-Raman spectroscopy, scanning electron microscopy, and in situ conductivity measurements at different pH and redox state.     

Toxicokinetics and metabolic study of 2,2′-dihydroxy-4,4′- dimethoxybenzophenone

2,2′-Dihydroxy-4,4′-dimethoxybenzophenone (UV-D) is one of the benzophenones, which is widely used as UV filter to protect industrial and commercial products from light. This compound is suspected as a kind of endocrine-disrupting chemical, which might interfere with hormonal signaling pathways, and have potential adverse effects on human health. Thus, toxicity and metabolism of it could be important to know its biological effect. As little is known about the toxicokinetics and metabolism of UV-D, herein, the related study was performed on rats by orally administrating with UV-D. UV-D was found to be promptly metabolized to five main metabolites, which were further identified by high-performance liquid chromatography–quadrupole time-of-flight mass spectrometry. Demethylation, hydroxylation, sulfonation, and glucuronidation were the main metabolic pathways for UV-D.     

Curing and thermal behaviour of a flame retardant cycloaliphatic epoxy resin based on phosphorus containing poly(amide–imide)s

The curing behaviour of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate was investigated by the dynamic differential scanning calorimetry (DSC) using phosphorus-containing poly(amide–imide)s (PAIs) having free amine groups, 4,4′-diaminodiphenylmethane (PM) and p-phenylenediamine (PA), in the ratio of 1:1. The PAIs were prepared by co-polymerization of diimide–diacid (DIDA) and phosphorus-containing triamines having phenylene moiety. l-Tryptophan and pyromellitic anhydride were used to synthesize DIDA. Triamines used in the synthesis PAIs were tris(3-aminophenyl) phosphine (TAP), tris(3-aminophenyl) phosphine oxide (TAPO) and bis(3-aminophenyl) aminotolyl phosphine (BAP). TAP-, TAPO- and BAP-containing PAIs were designated as PTAP, PTAPO and PBAP, respectively. These PAIs with free amine groups were characterized by FTIR, ¹H NMR, ¹³C NMR spectroscopic techniques and elemental analysis. The mixture of PAIs and PM or/and PA in the ratios of 0:1, 1:0 and 0.5:0.5 was used for investigation. DSC was used to study the curing of epoxy by recording the DSC scans at heating rates of 10 °C min^?1. Thermal stability of epoxy resin cured isothermally was evaluated by recording thermo gravimetric traces in nitrogen atmosphere at the heating rate of 20 °C min^?1. All samples are highly stable, and the 10 % mass loss found was in the range of 335–520 °C. The percent char yield was highest in case of resin sample E/PM/PTAPO. The flame-retardant properties of cured epoxy resins were investigated by the limiting oxygen index test (LOI) and UL94 test. When phosphorus was incorporated in epoxy resin, the epoxy resin system met the UL94 V-0 classification and the LOI reached at 37.8, because of nitrogen–phosphorus synergistic effect.