Studies on the curing kinetics of epoxy resins using mixture of nadic/or maleic anhydride and 4,4′-diaminodiphenyl sulfone

Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of maleic anhydride (MA)/or nadic anhydride (NA) or mixture of MA/NA: 4,4′-diaminodiphenyl sulfone (DDS) in varying molar ratios were investigated using differential scanning calorimetry. Curing behaviour of DGEBA in the presence of varying amounts of DDS:MA/NA was evaluated by recording DSC scans at heating rates of 5, 10, 15 and 20°C min⁻¹. The peak exotherm temperature depends on the heating rate, structure of the anhydride as well as on the ratio of anhydride: DDS. Thermal stability of the isothermally cured resins was evaluated by thermogravimetry. The char yield was highest in case of resins cured using mixture of DDS:MA (0.75:0.25; sample EM-1) and DDS:NA (0.75:0.25, sample EN-1).     

Weak noncovalent Si···F?C interactions stabilized fluoroalkylated rod-like polysilanes as ultrasensitive chemosensors

Noncovalent interactions, such as hydrogen bonding, metal coordination, and π-π stacking, are increasingly being utilized to develop well-ordered and self-organized supramolecular materials. Recently, new types of nonclassical weak interactions, such as C H···π, C H···F C, and C H···O, have been exploited in stabilizing the specific conformations of molecules and molecular assemblies in the solid state. These noncovalent interactions play an important role in materials comprised of polymer chains, because cooperative effects from a large number of weak interactions can lead to drastic changes in its conformation, several properties, and functionalities. The programmed design of synthetic helical polymer with well-defined molecular conformation has been the main subject in modern polymer science and engineering. Silicon-catenated polysilane is an ideal helical silicon quantum wire and polymers with unique photophysical properties. The present review highlights the spectroscopic evidences for through-space weak Si···F C interaction in poly(methyl-3,3,3-trifluoropropylsilane) ( 1 ) in noncoordinating and coordinating solvents by means of NMR (²⁹Si and ¹⁹F) and IR spectroscopies, and viscometric measurement. It was found that 1 is applicable for chemosensors with an extremely high sensitivity and selectivity toward fluoride ions in tetrahydrofuran (THF) and with high sensitivity for nitroaromatic compounds, detected by a decrease in the photoluminescence intensity in THF and in thin solid film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5060–5075, 2006     

Some compounds of iron(III) with bidentate bases

Summary The iron(III) compound, FeCl(OH)(MeCO₂) · MeCO₂H · 0.5 H₂O, (1), interacts with the sample bidentate ligand, 2,2-bipyridyl (bipy), to form an aduct, Fe₂Cl₂(OH)₂(MeCO₂)₂ · (bipy). By the loss of protons, anthranilic (anthH) and salicylic (salH₂) acids behave as uninegative charged ligands to give FeCl(anth)₂ · H₂O and FcCl(salH)₂ · H₂O, respectively. The former decomposes on heatingin vacuo to form Fe₂O(anth)₄ while the latter yields Fe₂O(sal)₂. Acetylacetone (acacH) and 8-hydroxyquinoline (quinH) give FeCl(acac)₂ and FeCl(quin)₂ · (quinH). The latter desolvates at 140°/10^–4 torr to form FeCl(quin)₂. l.r. spectra, thermal decomposition, molar conductance and magnetic susceptibility studies at room temperature have been used to characterize these compounds.     

Cooperative C-F...Si interaction in optically active helical polysilanes

Cooperative amplification of the C-F...Si weak interaction between side chains and the main chain was found to afford rigid rodlike helical polysilanes with a preferential screw sense.     

Binuclear iron(III) acetates

Summary The binuclear iron(III) compound, Fe₂Cl(OH)₂(MeCO₂)₃ 2 AcOH combines with pyridine, -picoline and 2,2-bipyridyl (B) to form Fe₂Cl(OH)₂(AcO)₃·B adducts. The secondary bases, pyrrolidine and diethylamine (RNH), on the other hand, combine with the complete elimination of chlorine to form, Fe₂(NR)(OH)₂(AcO)₃. These products have been characterised by molecular weight, i.r. spectra, magnetic susceptibility and Mössbauer measurements.     

Synthesis of polysilanes bearing pendant carbosilyl groups and Si-NMR probe on the tacticity using side chain silicon atoms

New functional polysilanes [R₂R¹Si(CH₂)₂SiH]_n (R=Me, R¹=H (1); R=R¹=Et (2); R=Me, R¹=Ph (3)) bearing carbosilyl side chains have been synthesized by catalytic dehydropolymerization of precursor carbosilanes R₂R¹SiCH₂CH₂SiH₃ using Cp₂TiCl₂–BuLi as a catalyst. These polymers are characterized by ¹H, ¹³C, ²⁹Si, {¹H–²⁹Si} HSQC NMR spectroscopy, GPC and TGA. Attempts to delineate the tacticity from the analysis of deconvoluted ²⁹Si{¹H}-NMR signals associated with the side chain silicon atoms reveal that the triad concentration ratio follows a Bernoullian statistical model for polymers 1 and 2 only.     

1,1,1,1-Tetrakis(o-fluorophenylamino)silane tris[titanium(IV) chloride]. Evidence for a new titanium cation [Ti2Cl7]+

Si(NHC₆H₄F-o)₄ · 3TiCl₄ (1) has been obtained from the disproportionation of (CF₃CH₂O)₃SiNHC₆H₄F-o and TiCl₄ in petroleum ether (40–60 °C) at –10 °C. The analytical (elemental analysis, molar conductance) and spectral (i.r., ¹H- and ¹⁹F-n.m.r.) data suggested that (1) behaves as [Si(NHC₆H₄F-o)₄ · Ti₂Cl₇]⁺ [TiCl₅]^–. The presence of these ions has been confirmed by characterising the products of metathetical reactions of (1) with R₄NX (R = Bu and Et; X = I and Br) and with AgNO₃. The data suggest the presence of a new titanium cation [Ti₂Cl₇]⁺.     

Effect of polymer and ion concentration on mechanical and drug release behavior of gellan hydrogels using factorial design

Developing optimized hydrogel products requires an in-depth understanding of the mechanisms that drive hydrogel tunability. Here, we performed a full 4 × 4 factorial design study investigating the impact of gellan, a naturally derived polysaccharide (1%, 2%, 3%, or 4% w/v) and CaCl₂ concentration (1, 3, 7, or 10 mM) on the viscoelastic, swelling, and drug release behavior of gellan hydrogels containing a model drug, vancomycin. These concentrations were chosen to specifically provide insight into gellan hydrogel behavior for formulations utilizing polymer and salt concentrations expanding beyond those commonly reported by previous studies exploring gellan. With increasing gellan and CaCl₂ concentration, the hydrogel storage moduli (0.1–100 kPa) followed a power-law relationship and on average these hydrogels had higher liquid absorption capability and greater total drug release over 6 days. We suggest that the effects of gellan and CaCl₂ concentration and their interactions on hydrogel properties can be explained by various phenomena that lead to increased swelling and increased resistance to network expansion.     

Convenient Microwave-Assisted Chlorosulfonic Acid-Catalyzed Synthesis of Some Quinazolinones from 2-Phenylindole

Russian Journal of Organic Chemistry - A new convenient method has been developed for the synthesis of quinazolinones from 2-phenyl-1H-indole and substituted amines under catalysis by...     

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.