Synthesis and characterization of Schiff-base-containing polyamides

A series of new Schiff base polyamides（PAs） were synthesized by polycondensation of benzilbisthiosemicarbazone diamine（LH₆） with different commercially available aliphatic and aromatic diacid chlorides. The monomer and all the PAs were characterized by FTIR,¹H-NMR,and elemental analysis.The prepared polyamides showed inherent viscosities in the range of 0.30-0.36 dL/g in DMF at 25℃,indicating their moderate molecular weight.The PAs were completely soluble in aprotic polar solvents such as dimethylformamide（DMF）,N-methylpyrolidone（NMP）, tetrachloroethane（TCE）,dimthylsulfoxide（DMSO） and also in H₂SO₄ and partially soluble in THF,acetone and chloroform at room temperature.Thermal analysis showed that these PAs were practically amorphous and exhibited 10%weight loss above 220℃.     

Synthesis and characterization of some novel aromatic polyimides

Three new diamines 1,2-di(p-aminophenyloxy)ethylene, 2-(4-aminophenoxy)methyl-5-aminobenzimidazole and 4,4-(aminopheyloxy) phenyl-4-aminobenzamide were synthesized and polymerized with 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropyledene)diphthalic anhydride (HF) and 3,4,9,10-perylene tetracarboxylic acid dianhydride (PD) either by one step solution polymerization reaction or by two step procedure. The later includes ring opening poly-addition to give poly(amic acid), followed by cyclodehydration to polyimides with the inherent viscosities 0.62-0.97 dl/g. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m-cresol even at room temperature and few becomes soluble on heating. The degradation temperature of the resultant polymers falls in the ranges from 240 °C to 550 °C in nitrogen (with only 10% weight loss). Specific heat capacity at 300 °C ranges from 1.1899 to 5.2541 J g⁻¹ k⁻¹. The maximum degradation temperature ranges from 250 to 620 °C. T_g values of the polyimides ranged from 168 to 254 °C.     

Synthesis and characterization of new polyimides containing ethynylene linkages

We have synthesized a series of new diamines containing bis(ethynylaniline) linkages by bromine substitution reaction of ethynylaniline with 4,4′-bis(4-bromophthalimido)diphenylether (PODA) or 1,4-bis(4-bromophthalimido)benzene (PPDA). The intermediates were separated at each step, purified and characterized by the spectroscopic techniques. The model compound having imide and triple bond moiety was synthesized in order to elucidate the nature of the products formed from the ethynyl curing by FT-IR spectroscopy. The polymerization reaction of ethynylaniline diamines with various dianhydrides gave fully imidized and soluble aromatic polyimides. The thermally cured polyimide samples displayed good solvent resistance. The thermal crosslinking of triple bond moieties in the main chain was carried out by heating in the temperature range from 150 to 400 °C. The glass transition temperature of polyimide completely disappeared after heat treatment at 400 °C for 5 min. The polyimides derived from diamines containing bis(ethynylaniline) groups were thermally stable after heat treatment.     

Synthesis and characterization of crosslinkable polyimides

A series of copolyimides were prepared from benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA) and various aromatic diamines which contain a fluorenyl group and/or alkyl substituents in ortho position to the amine groups. The effect of the chemical composition on the glass transition temperature (T_g), thermal stability as well as on the dielectric constant of these polymers was studied. High T_g polymers (T_g ranging from 260 °C to 370 °C), withstanding temperatures as high as 400 °C for 10 h and having a low dielectric constant (from 2.6 to 3.1) were successfully synthesized. All these polymers were able to crosslink under UV or thermal treatments.     

Homogenous one-pot synthesis of polyimides in polyphosphoric acid

A one-pot synthetic method to produce aromatic polyimides with high molecular weights from corresponding diamines and dianhydrides was developed, in which polyphosphoric acid (PPA) played a role of an excellent media for one-step synthesis of completely cyclized polyimides. The polymerization was carried out in the solid content of 10 wt/v% at 220 °C. The resulting products exhibited a homogeneous solution in the non-volatilizable PPA instead of precipitation form of the polyimides. The content of P₂O₅ in PPA had an influence on the molecular weight of the products, and the high percentage of P₂O₅ resulted in the relative high inherent viscosity. FTIR and Carbon-13 NMR were employed to analyze the structures and TGA was used to evaluate the thermal stability. The polyimides prepared by this one-step route exhibited good thermal properties and high values of activation energies for the degradation, on comparison with the polyimides prepared in DAMc by two-step polymerization method.     

Synthesis and characterization of fluorinated polyimides for pervaporation of n-heptane/thiophene mixtures

Soluble fluoro-polyimides have been synthesized by reacting of a fluorine-containing aromatic dianhydride, 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, with aromatic diamine to yield poly(amic acid)s which were then cyclized to yield polyimide by chemical imidization method. The polyimides have excellent solubility both in strong bipolar solvents, such as NMP and DMAc, and in common organic solvents, such as THF and dioxane, etc. The glass transition temperature of these polyimides were determined by DSC and ranged from 281 to 289 °C. Thermogravimetric analysis indicated that these polyimides have good thermal stability with initial thermal decomposition temperature of 520-526 °C. The polyimide asymmetric membranes were prepared by phase inversion method and the inner structure was observed by method of SEM. The pervaporation properties of the prepared polyimides asymmetric membranes for n-heptane/thiophene mixtures were investigated at 40-77 °C and the permeation flux and the sulfur enrichment factor of the polyimide membranes are in the range of 0.56-1.68 kg/m² h and 3.12-2.24, respectively. The result demonstrated that the pervaporation method could be very effective method for desulfurization by polyimides asymmetric membranes with ultrathin skin.     

Synthesis and characterization of some new Schiff base polymers

Seven Schiff base polymers poly 5,5^′-methylenebis(2-hydroxyacetophenone)semicarbazone (PHASC), poly-5,5^′-methylenebis(2-hydroxyacetophenone)thiosemicarbazone (PHATS), poly 6,6^′-methylenebis(2-hydroxynaphthaldehyde)1,2-propylenediimine (PHNPn), poly 6,6^′-methylenebis (2-hydroxynaphthaldehyde)1,3-propylenediimine (PHNPR), poly 6,6^′-methylenebis (2-hydroxy-naphthaldehyde)thiosemicarbazone (PHNTS), poly 6,6^′-methylenebis(2-hydroxy-naphthaldehyde)urea (PHNU) and poly-6,6^′-methylenebis(2-hydroxynaphthaldehyde)semicarbazone (PHNSC) were prepared by polycondensation of 5,5^′-methylenebis(2-hydroxyacetophenone) (MHA) or 6,6^′-methylenebis(2-hydroxynaphthaldehyde) (MHN) with semicarbazide, thiosemicarbazide, 1,2-propylenediamine, 1,3-propylenediamine or urea. The polymers were characterized by elemental micro-analysis, infrared and ultraviolet spectroscopy and viscosity measurements. The reduced viscosity of the polymers measured in dimethylformamide (DMF) was observed in the range 0.32-0.63 dl/g.     

Synthesis and characterization of new polyimides containing pendent pentadecyl chains

A new unsymmetrical aromatic diamine, viz., 4-pentadecylbenzene-1,3-diamine was synthesized through a series of reaction steps starting from 3-pentadecylphenol. 4-Pentadecylbenzene-1,3-diamine was employed to synthesize a series of new polyimides by one-step polycondensation in m-cresol with four commercially available aromatic dianhydrides, viz., 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA). Inherent viscosities of resulting polyimides were in the range 0.33-0.67 dL/g and number average molecular weights were in the range 14,700-52,200 (GPC, polystyrene standard). Polyimides containing pendent pentadecyl chains were soluble in organic solvents such as chloroform, m-cresol, N,N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidinone (NMP), pyridine and nitrobenzene. Strong and flexible films of polyimides could be cast from their chloroform solutions. Polyimides exhibited glass transition temperature in the range 158-206 °C. The temperature at 10% wt. loss (T₁₀), determined by TGA in nitrogen atmosphere, of polyimides was in the range 470-480 °C indicating good thermal stability.     

Organosoluble and thermally stable polyimides derived from a new diamine containing bulky-flexible triaryl pyridine pendent group

A novel kind of aromatic diamine,N-(4-(4-(2,6-diphenyl pyridine-4-yl)phenoxy)phenyl)-3,5-diaminobezamide (DPDAB),was synthesized via aromatic nucleophilic substitution of 3,5-dinitrobenzoylchloride with 4-(4-(2,6- diphenylpyridine-4-yl)phenoxy)aniline(DPPA),followed by palladium-catalyzed hydrazine reduction.This monomer was used to prepare polyimides(PIs)based on reaction with several commerically avaiable tetracarboxylic dianhydrides such as pyromellatic dianhydride(PMDA),benzophenone tetracarboxylic acide dianhydride(BTDA)and bicycle[2.2.2]oct-7-enc- 2,3,5,6-tetracarboxylic dianhydride(BCDA).These PIs had inherent viscosity in the range of 0.34-0.76 dL/g and showed good solubility in various aprotic polar solvents.The glass-transition tempratures(T_gs)of the PIs were in the range of 184-302℃,and showed high thermal stability with 10%weight loss in the temperature range of 360-500℃under nitrogen atmosphere.     

Organo-soluble and transparent polyimides containing phenylphosphine oxide and trifluoromethyl moiety: Synthesis and characterization

A series of aromatic polyimides (PI-II_a-d) containing lateral phenylphosphine oxide (PPO) and trifluoromethyl (-CF₃) moiety were prepared from an aromatic diamine, 2,5-bis[(4-amino-2-trifluoromethylphenoxy)phenyl]diphenyl-phosphine oxide (BATFDPO) and various aromatic dianhydrides via a two-step chemical imidization procedure. In parallel, for comparison, another series of polyimides (PI-I_a-d) without trifluoromethyl were synthesized from a diamine, 2,5-bis[(4-aminophenoxy)-phenyl]diphenylphosphine oxide (BADPO) and the same dianhydrides. It was found that both of the two series of polyimides (PIs) were soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and the solubility of PI-II_a-d was highly enhanced by the introduction of the bulky -CF₃ group. Flexible and tough PI films with tensile strengths higher than 70 MPa were cast from the PI solution. The introduction of -CF₃ moiety slightly sacrificed the thermal stability and mechanical properties of the PI films. For example, PI-II_a-d showed 5% weight loss at 472-476 ^°C, which was about 50 ^°C lower than those of their PI-I_a-d analogues. However, -CF₃ group apparently improved the optical transparency and decreased the refractive indices of the PI films. PI-II_d derived from BATFDPO and 4,4’-hexafluoroisopropylidenediphthalic anhydride (6FDA) exhibited the highest optical transparency with the transmittance of 90% at 400 nm and the refractive index as low as 1.5511 at 1310 nm.     

Synthesis,characterization and in vitro antimicrobial activity of some novel 5-substituted Schiff and Mannich base of isatin derivatives

With the aim of developing potential antimicrobials, a series of novel Ciprofloxacin methylene isatin derivatives incorporating different aromatic aldehydes were synthesized and characterized by FTIR, ¹H NMR, Mass spectroscopy and bases of elemental analysis. In addition, the in vitro antibacterial and antifungal properties were tested against some human pathogenic microorganisms by employing the disc diffusion technique. A majority of compounds were showing activity against several of the microorganisms. The relationship between the functional group variation and the biological activity of the evaluated compounds is discussed. From comparisons of the compounds, 3c was determined to be the most active compound.     

Synthesis,characterization, antimicrobial,and nuclease activity studies of some metal Schiff-base complexes

A Schiff base (L) is prepared by condensation of cuminaldehyde and L-histidine, and characterized by elemental analysis, IR, UV-Vis, ¹H-NMR, ¹³C-NMR, and mass spectra. Co(II), Ni(II), Cu(II), and Zn(II) complexes of this Schiff-base ligand are synthesized and characterized by elemental analysis, molar conductance, mass, IR, electronic spectra, magnetic moment, electron spin resonance (ESR), CV, TG/DTA, powder XRD, and SEM. The conductance data indicate that all the complexes are 1 : 1 electrolytes. IR data reveal that the Schiff base is a tridentate monobasic donor, coordinating through azomethine nitrogen, imidazole nitrogen, and carboxylato oxygen. The electronic spectral data and magnetic measurements suggest that Co(II) and Ni(II) complexes are tetrahedral, while Cu(II) complex has distorted square planar geometry. XRD and SEM show that Co(II), Cu(II), and Zn(II) complexes have crystalline nature, while the Ni(II) complex is amorphous and the particles are in nanocrystalline phase. The in vitro biological activities of the synthesized compounds were tested against the bacterial species, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus; and fungal species, Aspergillus niger, Aspergillus flavus, and Candida albicans by the disc diffusion method. The biological study indicates that complexes exhibit more activity than the ligand. The nuclease activity of the ligand and its complexes are assayed on CT DNA using gel electrophoresis in the presence and the absence of H₂O₂. The Cu(II) complex shows increased nuclease activity in the presence of an oxidant when compared to the ligand, Co(II) and Ni(II) complexes.     

Synthesis,characterization, and thermodynamic studies of the interaction of some new water-soluble Schiff-base complexes with bovine serum albumin

Some new water-soluble Schiff-base complexes Na₂[M(5-SO₃-2,3-salpyr)(H₂O) _n ]?·?2H₂O (5-SO₃-2,3-salpyr?=?N,N′-bis(5-sulphosalicyliden)-2,3-diaminopyridine and M?=?Zn, Cu, Ni) were synthesized and characterized by elemental analysis, IR, ¹H NMR, magnetic susceptibility measurement, thermal analysis, and UV-Vis spectroscopy. The mechanism of binding of Na₂[M(5-SO₃-2,3-salpyr)(H₂O) _n ]?·?2H₂O with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. The fluorescence titration revealed that the intrinsic fluorescence of BSA was quenched by Na₂[M(5-SO₃-2,3-salpyr)], which was rationalized in terms of the static quenching mechanism. The values of the Stern–Volmer constants, quenching rate constants, binding constants, binding sites, and average aggregation number of BSA were determined by this method. Thermodynamic parameters were calculated by the van’t Hoff equation. The data clearly indicate that the binding is entropy driven and enthalpically disfavored. Based on the Förster theory of non-radiative energy transfer, the efficiency of energy transfer, and the distance between the donor (Trp residues) and the acceptor (Na₂[M(5-SO₃-2,3-salpyr)]) were evaluated. Also the synchronous fluorescence spectra showed that the microenvironment of the tryptophan residues was not changed. Finally, our results indicate that the complexes can bind to BSA and be efficiently transported in the body, which could be helpful for further drug design.     

Synthesis,spectroscopic characterization and thermal studies of some rare earth metal complexes of unsymmetrical tetradentate Schiff base ligand

The solid complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) with 4-hydroxy-3-(1-{2-(2-hydroxy-benzylidene)-aminophenylimino}-thyl)-6-methy-pyran-2-one (H₂L) derived from o-phenylenediamine, 3-acetyl-6-methyl-(2H)pyran,2,4(3H)-dione (dehydroacetic acid or DHA) and salicylic aldehyde have been synthesized and characterized by elemental analysis, conductometry, magnetic susceptibility, UV–visible, FTIR, ¹H NMR spectra, X-ray diffraction, and thermal analysis and screened for antimicrobial activity. The FTIR spectral data suggest that the ligand behaves as a dibasic tetradentate ligand with ONNO donar atoms sequence towards central metal ion. From the microanalytical data, the stoichiometry of the complexes has been found to be 1:1 (metal:ligand). The physico-chemical data suggest distorted octahedral geometry for La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) complexes. The X-ray diffraction data suggest monoclinic crystal system for La(III) and Ce(III) and orthorhombic crystal system for Pr(III) and Nd(III) complexes. Thermal behaviour (TGA/DTA) of the complexes was studied and kinetic parameters were determined by Horowitz–Metzger and Coats–Redfern methods. The ligand and their metal complexes were screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Bacillus sp. Fungicidal activity against Aspergillus niger, Trichoderma and Fusarium oxysporum.     

Synthesis and mechanical properties of novel photosensitive polyimides

This paper surveys novel photoimageable polyimides (PHIMPI), with emphasis on synthesis. Details of the chemistry and synthesis techniques on PHIMPI are discussed. A number of associated issues such as swelling, storage stability, shrinkage, photospeed, solvent developability, moisture absorption, thermal expansion and mechanical properties are presented. Most of the photoimageable polyimides that are commercially suitable to date are negative-acting, although recent developments in positive-acting PHIMPI are included.     

Synthesis and properties of a novel polyester containing bithiazole

A novel Schiff base type polyester containing 2,2’-diamino-4,4’-bithiazole(DABT) was prepared by low-temperature interface polycondensation of 1,4-benzenedicarbonyl dichloride with 4,4’-(4,4’-bithiazole-2,2’-diylbis(imine-2,1-diyl)diphenol(BDDP), which is derived from a 2,2’-diamino-4,4’-bithiazole(DABT) Schiff base reacted with a 4-hydroxybenzaldehyde monomer.The newly generated polyester was evaluated based on characterization of its solubility,FTIR spectroscopy,elemental analysis,X-ray diffraction measurements and thermogravimetric analysis(TGA) studies.     

三氮唑类席夫碱的合成及其荧光性能

近年来,Schiff碱因其结构的多样化以及具有光、电、磁等物理材料性能[1-3]的配位化学性能[4-5]等引起人们的关注,同时一些特殊结构的Schiff碱的合成和性质研究具有更为重要的理论意义和应用价值.     

Synthesis and characterization of sulfonated naphthalenic polyimides based on 4,4′-diaminodiphenylether-2,2′-disulfonic acid and bis[4-(4-aminophenoxy)phenylhexafluoropropane] for fuel cell applications

The paper describes the synthesis and characterization of sulfonated polyimides based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 4,4′-diaminodiphenylether-2,2′-disulfonic acid (ODADS) and (bis[4-(4-aminophenoxy)phenylhexafluoropropane] (BDAF)). Several copolymer samples were prepared by varying the molar ratio of ODADS: BDAF (0.5:1.50, 0.75:1.25, 1:1 and 1.50: 0.5) in the initial monomer feed. Structural characterization of the copolymers was done using FT-IR and ¹H NMR. ¹H NMR was also used to calculate the copolymer composition. Thermal characterization was done using thermogravimertry and dynamic mechanical analysis. Polymer films were prepared by solution casting using m-cresol as solvent. The membranes thus prepared were characterized for water uptake, water stability, methanol permeability and proton conductivity. The obtained sulfonated polyimides (SPI’s) had proton conductivities in the range of 0.137-3.94 mS/cm. SPI’s with 50% degree of sulfonation had proton conductivity comparable to that of Nafion with methanol permeability lower than that of Nafion. It was found that the degree of sulfonation of polyimide had a large effect on the thermal stability, water uptake, ion-exchange capacity and proton conductivity.     

Synthesis,characterization, and antimicrobial studies of some Schiff-base metal(II) complexes

Neutral complexes of Co(II), Ni(II), Cu(II), and Zn(II) have been synthesized from the Schiff bases derived from 3-nitrobenzylidene-4-aminoantipyrine and aniline (L¹)/p-nitro aniline (L²)/p-methoxy aniline (L³) in the molar ratio 1 : 1. The structural features have been determined from microanalytical, IR, UV-Vis, ¹H-NMR, mass, and ESR spectral data. The Cu(II) complexes are square planar, while Co(II), Ni(II), and Zn(II) complexes are tetrahedral. Magnetic susceptibility measurements and molar conductance data provide evidence for the monomeric and neutral nature of the complexes. The X-band ESR spectrum of Cu(II) complexes at 300 and 77 K were recorded. The electrochemical behavior of the complexes in MeCN at 298 K was studied. The in vitro biological screening effects of the investigated compounds were tested against the bacterial species Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, and Pseudomonas aeruginosa and fungal species Aspergillus niger, Rhizopus stolonifer, Aspergillus flavus, Rhizoctonia bataicola, and Candida albicans by the well-diffusion method. Comparison of the inhibition values of the Schiff bases and their complexes indicate that the complexes exhibit higher antimicrobial activity.