Effect of melamine polyphosphate on thermal degradation of polyamides: a combined X-ray diffraction and solid-state NMR study

The effect of melamine polyphosphate (MpolyP) on the thermal degradation of both polyamide 66 (PA66) and polyamide 6 (PA6) was studied using a combination of solid-state techniques. The mixtures of MpolyP with polyamides were heated for different times at 350 and 450 °C. The residues were then analyzed by X-ray diffraction and both solid-state ¹³C NMR and ³¹P NMR. The chemical structures formed in these oven experiments were used to study the chemical changes that take place during a standard flammability test. The mixtures of MpolyP with polyamides were also characterized by frequency-dependent rheological experiments. It was shown that MpolyP could induce significant cross-linking in PA66 and leads to dramatic depolymerization of PA6. These results were used to explain the performance of MpolyP as a flame retardant in these polyamides.     

Synthesis,characterization, and curing of unsaturated polyamides derived from 2,6-di(4-carboxystyryl)pyridine and 2,6-bis(4-carboxybenzylidene) cyclohexanone

Two new series of heat-curable polyamides were prepared utilizing the unsaturated dicarboxylic acids 2,6-di(4-carboxystyryl)pyridine (DCSP) and 2,6-bis(4-carboxybenzylidene)cyclohexanone (BCBC) as starting materials. They were prepared from the condensation of 4-carboxybenzaldehyde with a half molar amount of 2,6-dimethylpyridine or cyclohexanone, respectively. The dicarboxylic acids reacted with various aromatic diamines, utilizing triphenyl phosphite and pyridine as condensing agents, to yield polyamides. In addition, two model diamides were prepared by condensing the dicarboxylic acids with aniline. Characterization of starting materials, polyamides, and model compounds was accomplished by IR and ¹H–NMR spectroscopy. The curing behavior of polyamides was investigated by DTA. Upon heat-curing, the unsaturated polyamides were crosslinked through their olefinic bonds to afford insoluble, heat-resistant resins. The thermal stability of the resins was evaluated by TGA and isothermal gravimetric analysis (IGA). The cured resins were stable up to 310–322°C in N₂ or air and afforded anaerobic char yield of 57–69% at 800°C.     

Elastic modulus in the crystalline region of poly(p-phenylene terephthalamide)

Fibres from aromatic polyamides have a much higher Young's modulus than fibres from aliphatic polyamides. In order to contribute to the explanation of this observed difference we looked at one of the ultimate properties, the elastic modulus in the crystalline region in the chain direction (E_cr∥). We carried out measurements on a bundle of filaments of PRD 49 fibre, which we identified by i.r. and X-ray analyses as poly(p-phenylene terephthalamide). With the X-ray technique we determined the lattice extensions under loading and from these data the E_cr∥ was calculated. The E_cr∥ was found to be 20 × 10¹¹ dyne/cm² which is in good agreement with the calculated E_cr∥, but not very different from that of nylon-6,6. The Young's modulus was found to be 11 × 10¹¹ dyne/cm².     

Investigation of the Polyamide 6,6 dyeing process with Acid Blue 45 dye. Part I. Thermodynamics of Acid Blue 45 adsorption

Among the many synthetic fibres, polyamides are one of the most important. Improvement in the adsorption/ absorption strength of a dye to and inside the yarns is therefore very important for their practical applications. In this study, the kinetics and thermodynamics of the sorption process of Acid Blue 45 on Polyamide 6,6 (Nylon 6,6) were investigated. The sorption was conducted at 293, 303, and 313 ± 0.1 K for 48 h from 10^-5 -10^-4 M solutions in the presence of 10^-3 M NaCl. From the kinetic experiments it was found that this time was sufficient to attain the adsorption equilibrium. The first stage of the sorption (up to 160 min) can be well described by a first-order kinetic equation by its numerical fitting to the experimental results. It is a spontaneous process in which the rate of sorption and the sorbed amount increase with increasing temperature. However, it is a relatively slow endothermic process (positive enthalpy of sorption); thus, it must be entropy-driven to produce a negative free energy of sorption. From the sorption isotherms and calculated thermodynamic functions it can be concluded that at higher temperatures (303-313 K), more polar groups of Polyamide 6,6 are accessible for the dye molecules, which may be due to a glass transition. Data on the zeta potential changes and surface free energy components of Polyamide 6,6 will be presented in Part II of this study, which may help in a better understanding of the sorption process.     

The nucleation effect of linear polyethylene lamellae over the crystallization of branched polyethylene

Summary The polyamides with aromatic rings in the main chain were synthesized by the solution polymerization of 4,4-diphenylmethane diisocyanate and aliphatic dicarboxylic acid in the presence of catalyst. The thermal properties and the miscibility behaviours with polyamide-6,6 of these aromatic polyamides were studied. The aromatic polyamides synthesized with one kind of dicarboxylic acid had typical thermal properties of crystalline polymers, whereas those synthesized with the mixtures of dicarboxylic acids were not easily crystallized. The observed miscibility behaviours showed some differences from those predicted by binary interaction model.     

Synthesis and characterization of new polyamides and copolyamides containing 6,6'-sulfonediquinoline units

Summary Aromatic polyamides were obtained by the direct polycondensation reaction of a new monomer containing a 6,6'-sulfonediquinoline unit with various aromatic diamines. The polymers were characterised by elemental, infrared, wide angle X-ray diffraction and thermal analysis. The polyamides, possessed inherent viscosities in the range 0.24 – 0.43 dl g⁻¹, 10% weight loss in nitrogen and air above 410°C and glass transition temperatures in the range 170–220°C. The polyamides obtained by reaction with 4,4'-methylenedianiline and 4,4'-sulfonyldianiline were soluble on heating in N-methyl-2-pyrrolidinone and partially soluble in dimethylacetamide. Solubility and thermal properties of copolyamides, prepared from the reaction of 4,4'-oxydianiline with the new monomer and the 4,4'-dicarboxydiphenyl sulfone, were also studied. Received: 5 October 1998/Revised version: 19 April 1999/Accepted: 19 April 1999     

Synthesis and properties of novel poly(coumarin‐amide)s

A novel monomer diacid, 6,6′‐methylenebis(2‐oxo‐2H‐chromene‐3‐carboxylic acid), was synthesized and used in a direct polycondensation reaction with various aromatic diamines in N‐methyl‐2‐pyrrolidone solution containing dissolved LiCl and CaCl₂, using triphenyl phosphite and pyridine as condensing agents to give a series of novel heteroaromatic polyamides containing photosensitive coumarin groups in the main chain. Polyamide properties were investigated by DSC, TGA, GPC, wide‐angle X‐ray scattering, viscosity, and solubility measurements. The copolymers were soluble in aprotic polar solvents, and their inherent viscosities varied between 0.49 and 0.78 dL g^?1. The weight‐average and number‐average molecular weights, measured by gel permeation chromatography, were 27,500–43,900 g mol^?1 and 46,500–66,300 g mol^?1, respectively, and polydispersities in the range of 1.48–1.69. The aromatic polyamides showed glass‐transition temperatures (T_g) ranging from 283 to 329°C and good thermal properties evidenced by no significant weight loss up to 380°C and 10% weight loss recorded above 425°C in air. All the polyamides exhibited an amorphous nature as evidenced by wide‐angle X‐ray diffraction and demonstrated a film forming capability. Water uptake values up to 3.35% were observed at 65% relative humidity. These polymers exhibited strong UV‐vis absorption maxima at 357–369 nm in DMSO solution, and no discernible photoluminescence maxima were detected by exciting with 365 nm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of high performance polyamides utilizing copper‐catalyzed amidation of a dibromoarene with different diamides

A series of diphenylquinoxaline‐containing polyamides were prepared from the condensation polymerization of 2,3‐bis (4‐bromophenyl) quinoxaline (DBQ) with various primary and secondary diamides via copper‐catalyzed amidation reaction. The polyamides were characterized with FTIR, NMR, GPC, differential scanning calorimeter, and thermo gravimetric analysis, and their solubility and viscosity were measured. The polyamides synthesized here are amorphous and showed relatively good solubility in polar aprotic solvents and demonstrate the ability to form brownish hard films by solvent casting; their inherent viscosities ranged from 49 to 55 mL/g. The average molecular weights of polyamides were in the range of M_w = 11,950–5592 g/mol (MWD = 1.21–1.87). These polyamides had relatively high thermal stability with T_g values up to 276°C, 10% weight loss temperatures (T_10%) in the range of 364–476°C, and char yields at 600°C in N₂ up to 72%. They also exhibit emission in the solid state and in dilute (0.2 g/dL) DMAc solution at 425–484 nm with photoluminescence quantum (?_f) yields in the range of 14–23%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of novel aromatic polyamides derived from 2,2′‐bis(p‐phenoxyphenyl)‐4, 4′‐diaminodiphenyl ether

BACKGROUND: Wholly aromatic polyamides (aramids) are high‐performance polymeric materials with outstanding heat resistance and excellent chemical stabilities due to chain stiffness and intermolecular hydrogen bonding of amide groups. Synthesis of structurally well‐designed monomers is an effective strategy to prepare modified forms of these aramids to overcome lack of organo‐solubility and processability limitations. RESULTS: A novel class of wholly aromatic polyamides was prepared from a new diamine, namely 2,2′‐bis(p‐phenoxyphenyl)‐4,4′‐diaminodiphenyl ether (PPAPE), and two simple aromatic dicarboxylic acids. Two reference polyamides were also prepared by reacting 4,4′‐diaminodiphenyl ether with the same comonomers under similar conditions. M?_w and M?_n of the resultant polymers were 8.0 × 10⁴ and 5.5 × 10⁴ g mol^?1, respectively. Polymers resulting from PPAPE exhibited a nearly amorphous nature. These polyamides exhibited excellent organo‐solubility in a variety of polar solvents and possessed glass transition temperatures up to 200 °C. The 10% weight loss temperatures of these polymers were found to be up to 500 °C under a nitrogen atmosphere. The polymers obtained from PPAPE could be cast into transparent and flexible films from N,N‐dimethylacetamide solution. CONCLUSION: The results obtained show that the new PPAPE diamine can be considered as a good monomer to enhance the processability of its resultant aromatic polyamides while maintaining their high thermal stability. The observed characteristics of the polyamides obtained make them promising high‐performance polymeric materials. Copyright © 2009 Society of Chemical Industry     

New Diamides of 2,2′-dipyridyl-6,6′-dicarboxylic Acid for Actinide-Lanthanide Separation

The extraction of americium and lanthanides by diamides of 2,2′-dipyridyl-6,6′-dicarboxilic acid solutions in polar diluents was investigated. The dependence of extraction properties of the diamides on their structure was studied and the distribution ratios of americium and lanthanides from nitric acid solutions were determined. The highest extraction was found for the compounds with the ethyl-group and the alkyl-substituted aryl-group on the amidic nitrogen. The Am/Ln separation factors higher than 10 were achieved for extraction from high acidity media.     

Synthesis and characterization of polyamides X 18

Step heating melt polycondensation was adopted in the preparation of polyamides based on 1,16‐octadecane diacid and α,ω? (CH₂)_2n diamines (n = 1–6). The structure was confirmed by various spectroscopic techniques (IR, Raman, ¹H‐NMR, and ¹³C‐NMR). High molecular masses were obtained only in the presence of an excess of diamine and when the diamine possessed low volatility. The molecular masses were between (0.94 and 2.1) × 10⁴ Da for all polyamides under consideration. An excellent correlation between size exclusion chromatography and ¹H‐NMR data was demonstrated in the measurement of the degree of polymerization. The melting temperatures of the polyamides decreased from polyamide 12 18 to polyamide 2 18 as the amide density along the molecular chain declined. No significant variation was observed in the glass‐transition and decomposition temperatures of the polyamides that were obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1565–1571, 2005     

Thermally reversible cross-linked polyamides and thermo-responsive gels by means of Diels-Alder reaction

Cross-linked polyamides and polyamide gels were prepared from maleimide-containing polyamides and a tri-functional furan compound and showed thermal reversibility in cross-linking behavior and in gel formation through Diels-Alder (DA) and retro-DA reactions. The rate constant k of the DA cross-linking reaction were 1.25-4.83×10⁻⁵ dm³ mol⁻¹ s⁻¹ in the temperature range of 20-60 °C with an activation energy of 32.1 kJ mol⁻¹. The cross-linking densities, thermal properties, and thermal reversibility of the polyamides/furan polymers were adjustable with the contents of maleimide groups in polyamides.     

Properties of films and fibers obtained from Lewis acid-base complexed nylon 6,6

A nylon 6,6 complex with GaCl₃ in nitromethane (4-5 wt% nylon 6,6) was prepared at 50-70 °C over 24 h for the purpose of disrupting the interchain hydrogen bonding between nylon 6,6 chains, resulting in amorphous nylon 6,6, and increasing the draw ratio for improving the performance of nylon 6,6 fibers. After drawing, complexed films and fibers were soaked in water to remove GaCl₃ and regenerate pure nylon 6,6 films and fibers. FTIR, SEM, DSC, TGA, and mechanical properties were used for characterization of the regenerated nylon 6,6 films and fibers. The amorphous complexed nylon 6,6 can be stretched to high draw ratios at low strain rates, due to the absence of hydrogen bonding and crystallinity in these complexed samples. Draw ratios of 7-13 can be achieved for complexed fibers, under low strain rate stretching. This study indicates that nylon 6,6 fibers made from the GaCl₃ complexed state, using a high molecular weight polymer, can reach initial moduli up to 13 GPa, compared to initial moduli of 6 GPa for commercial nylon 6,6 fibers. Lewis acid-base complexation of polyamides provides a way to temporarily suppress hydrogen bonding, potentially increasing orientation while drawing, and following regeneration of hydrogen bonding in the drawn state, to impart higher performance to their fibers.     

Nylon 6,6 copolyamides of bis(2-carboxyethyl) methylphosphine oxide

Copolyamides of nylon 6,6 with bis(2-carboxyethyl)methylphosphine oxide (CEMPO) were prepared by melt polycondensation of nylon 6,6 salt with CEMPO and hexamethylene diamine. The effect of CEMPO upon melting point, moisture regain, boiling water shrinkage, water wicking, tensile properties, thermal stability, static dissipation, and flammability of nylon 6,6 fibers and fabrics was determined. The fiber properties were greatly affected by the high water absorption and solubility characteristics of the phosphine oxide linkage. However, crystallinity and orientation were not greatly disturbed by up to 30–40M% CEMPO substitution in nylon 6,6. The copolyamides were of improved flame resistance compared to nylon 6,6 and were also found to give improved flame resistance in blends of the copolymer with various commercial plastics. In addition, CEMPO and the corresponding diamine, bis(3-aminopropyl)methylphosphine oxide were used to prepare a series of cycloaliphatic and aromatic ring-containing polyamides, but problems were encountered with moisture sensitivity and low melting points with some of these polymers.     

Methanol oxidation at carbon supported Pt and Pt-Ru electrodes: an on line MS study using technical electrodes

Methanol oxidation at technical carbon based electrodes in 0.05 M H₂SO₄ has been investigated by cyclic voltammetry using online MS under the conditions of an acid methanol fuel cell (DMFC). 5% Pt on Norit BRX and 30% Pt/Ru (40/60) on Norit BRX were used as catalysts. It is shown that methanol oxidation at technical electrodes can be characterized by a combination of cyclic voltammetry and mass spectroscopy. The onset potentials and potential dependences of the methanol oxidation rate can be determined directly by monitoring the formation of CO₂. Onset potentials of 0.5V and 0.25 V/RHE have been measured for Pt and Pt-Ru catalysts, respectively. The onset of methanol oxidation can be shifted to even more cathodic potentials (0.2V) if the Pt-Ru electrode reduces oxygen simultaneously. Carbon monoxide gas was also purged into the methanol containing electroyte during measurement in order to investigate the catalyst performance under more adverse conditions. C¹³-labelled methanol was used to distinguish between CO₂. formed from methanol (m/e = 45) and CO-oxidation (m/e = 44). Without CO the use of C¹³-labelled methanol enabled a distinction between methanol oxidation and carbon corrosion. The methanol oxidation at the platinum catalyst is severely inhibited by the presence of CO, shifting its onset to 0.65 V/RHE. In contrast the performance of the Pt-Ru electrode is not seriously affected under these conditions. It is concluded that Pt-Ru is an excellent catalyst for a methanol anode in an acid methanol fuel cell (DMFC).     

Synthesis of Soluble,Curable, and Thermally Stable Aromatic Polyamides Bearing Thiourea and Pendent 4-Pyridylformylimino Groups

A new aromatic dicarboxylic acid monomer 4-pyridylformylimino-N-(phenyl,2′,5′ – dicarboxylic acid) (PPDC) containing pyridine and azomethine units was synthesized through a simple one-step condensation reaction between 2-aminoterephthalic acid and 4-pyridinecarboxaldehyde. A series of new polyamides was prepared through the direct one-pot phosphorylation polycondensation of PPDC with simple aromatic commercial diamines and diamines bearing phenylthiourea groups. The polyamides were characterized by FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. Thermal stability of the polymers was evaluated using thermogravimetric analysis. The polyamides with inherent viscosities in the range of 0.30–0.51 dL/g showed an outstanding solubility in various solvents such as 1-methyl-2-pyrrolidone (NMP), dimethly sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimetylacetamide (DMAc), and pyridine. The cured polyamides displayed significantly higher thermal stability than the uncured polyamides. The conductivity of the polyamides, when blended with 20% by weight of doped polyanilines, was in the range 3.09–4.21 × 10^?3 S cm^?1.     

Synthesis and study of the effect of carboxyvinyl group position on the properties of polyamides. Crosslinked polymers

Several aromatic polyamides containing carboxyvinyl bonds in the main chain were synthesized by self-condensation from β-(2-,3-,4-aminophenyl)propenoic acid using the phosphorylation method. In addition, aromatic polyamides containing carboxyalkyl bonds in the backbone were synthesized under the same conditions for comparative purposes (model polyamides) and used as pattern. The model polyamides were synthesized from 3-,4-aminophenyl acetic acid and β-(3-aminophenyl)propanoic acid. Polymers were characterized by UV–vis, FT-IR and ¹H-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and inherent-viscosity measurement. The effect of the carboxyvinyl group position in the aromatic ring was correlated to polyamides properties. Thereby, solubility, thermal stability, viscosities, optical properties, and polymers crosslinking were studied. Some polyamides were soluble in polar solvents and inorganic acids. Upon thermal curing crosslinked polymers were obtained. The thermal stability and crosslinking of polyamides were evaluated with respect to position of carboxyvinyl in the aromatic ring. The crosslinked polymers exhibited improved thermal stability.     

Über den thermischen Abbau von Polyamiden der Nylon-Reihe

Several aliphatic polyamides (nylon-7, nylon-12, nylon-4, nylon-6,6, nylon-6,10, nylon-4,10, nylon-11,6, nylon-12,12) have been investigated in a mass spectrometer. Cyclic oligomers, which evaporate in the high vacuum of the ion source at temperatures below 200°C can be detected without previous isolation. The start of a thermal decomposition can be observed via the total ion current at temperatures above 350°C. Under those conditions polyactams are degraded by ring-chain equilibration into cyclic oligomers, whereas the favoured decomposition of polyamides of dicarboxylic acids and diamines is a cis elimination and the cleavage of the amide bond. With an increasing content of methylene groups these mechanisms also occur in polylactams. Mass spectra recorded of each polyamide at 170°C and ca. 400°C are characteristic and can be used for a fast identification and differentiation.     

Crosslinking of polyamides using dianhydrides,diacid chloride and dialdehyde: a promising approach for water treatment

New crosslinked polyamides were successfully produced from the condensation of pre‐synthesized monomer, 5‐(2,2,2‐trifluoroacetamido)isophthaloylchloride (TFAIAC) and diamines at low temperature. These polyamides were used as promising metal‐chelating adsorbents due to the presence of O and N donor sites on the crosslinked polyamides. For this purpose, trifluoroacetic anhydride was used to protect the amino group of 5‐aminoisophthalic acid, thus generating 5‐(2,2,2‐trifluoroacetamido)isophthalic acid (TFAIA). TFAIA was converted into TFAIAC using oxalyl chloride, which was exploited as a suitable monomer for the synthesis of aromatic polyamides. Amino groups were then set free under basic conditions and the crosslinking was carried out through amino groups present on the polyamide chains with different dianhydrides, isophthaloyl chloride and 2,5‐thiophenedicarboxaldehyde. The synthesis of monomers and polymers was confirmed by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy and molar masses of the polyamides were measured by gel permeation chromatography. The crosslinked macromolecules were found to possess enough chain alignment as depicted by their XRD patterns. The thermal stability of the crosslinked polyamides was increased as their decomposition temperatures were improved from 420 to 619 °C. Metal ion uptake was scrutinized through atomic absorption spectroscopy with 83%–85% adsorption capacity at optimized parameters, i.e. a contact time of 3 h at pH 6. The mechanism of adsorption was further investigated through the Freundlich and Langmuir adsorption isotherms. The results reveal that uptake of metal ions followed monolayer adsorption of cations owing to coordination to electronegative centers on the macromolecules, confirming the Langmuir adsorption model. © 2019 Society of Chemical Industry     

Depolymerization of Turkish lignites. 2. Effect of phenol concentration in a closed system

A lignite (C, 66.9 wt%) was depolymerized, using sulphuric acid as a catalyst, in a closed system in which the phenol/coal ratio was varied from 1.5 to 10. The products were separated by solvent extraction and silica gel chromatography. The i.r. and n.m.r. spectra, and the molecular weight of the products were measured. In the experiments with a phenol/coal ration of 10, complete depolymerization of the coal was seen provided the temperature of depolymerization was at least 210 °C. The products generally contained disubstituted aromatic structures connected by methylene bridges, it was found that as the phenol/coal ratio was increased there was a decrease in the number of methylene bridges connecting the aromatic structures. The molecular weights of the straight-chain pentane and benzene-soluble material were lower than the molecular weights of similar fractions in depolymerization experiments carried out in open systems. A method for the structural analysis of straight-chain pentane and benzene-soluble material based on i.r., ¹H n.m.r. and molecular weight measurements is suggested.