Novel aromatic and aromatic–aliphatic poly(thiourea‐amide)s for the extraction of toxic heavy metal ions

A series of novel aromatic and aromatic–aliphatic diamines [isophthaloyl bis(3‐(3‐aminophenyl)thiourea), terephthaloyl bis(3‐(3‐aminophenyl)thiourea), adipoyl bis(3‐(3‐aminophenyl)thiourea), sebacoyl bis(3‐(3‐aminophenyl)thiourea)] were synthesized starting from the dinitro compounds. Spectroscopic and elemental analyses were carried out for the structure elucidation of the monomers. Three series of poly(thiourea‐amide)s (PTAMs) bearing C?S groups were prepared through the condensation of new diamines with the diacid chlorides such as isophthaloyl, terephthaloyl and adipoyl chloride. The ensuing PTAMs were characterized using FTIR, ¹H‐NMR and ¹³C‐NMR techniques. Physical properties of the polymers such as solution miscibility, crystallinity, solution viscosity, molecular weight, and thermal properties were measured. Consequently, good organosolubility of these polymers was experiential in amide solvents as DMAc, DMF, DMSO and NMP. Moreover, PTAMs exhibited η_inh in the range of 0.92–1.56 dL/g and GPC measurements revealed M_w around 607 × 10²‐851 × 10². DSC served to envisage the glass transition temperatures (T_g) of poly(thiourea‐amide)s located between 232 and 258°C and the initial decomposition temperatures (T₀) probed by thermogravimetry were in the range of 305–419°C. Structure‐property relationship of these polymers was also studied. Eventually, solid?liquid extraction tests of the selected poly(thiourea‐amide)s systems revealed excellent results because these polymers show nearly 100% elimination of lead and mercury cations from water media. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of novel organosoluble biosourced poly(ester imide)s based on 1,4:3,6 -dianhydrohexitols suited for adhesives applications

A new series of poly(ester imide)s were prepared from the polycondensation of isosorbide and a series of synthesized diacyl chloride monomers based on a reaction between 1,2,4-Benzenetricarboxylic anhydride (TMA) and various diamines. The structures of the resulting polymers were confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹³C NMR spectra. Inherent viscosities and size exclusion chromatography (SEC) measurements proved the formation of high molecular weight poly(ester imide)s. The thermogravimetric analysis (TGA) showed deterioration temperature in the range of 221–400 °C indicating a good thermal stability. The differential scanning calorimetry (DSC) measurements revealed high glass transition temperature in the range of 67–185 °C. Wide angle X-ray diffraction measurements showed that the studied poly(ester imide)s were semi-crystalline. Most of the synthesized poly(ester imide) exhibited a good adhesion ability and tensile strength values comparable to analogous polymers.     

New poly(bisbenzoylamine imide) series: Synthesis and characterization

Three new series of poly(bisbenzoylamine imide)s, incorporating different aromatic diamines, have been synthesized. The polymers, obtained by the two-step procedure, have been characterized by DSC, TGA, X-ray, FTIR, and ¹H-NMR methods. Thermal analysis showed glass transition temperatures in the range of 200°–250°C and decomposition at 430°–495°C. Most DSC runs displayed an exothermic event above T_g that was due to cold crystallization of the polymer molecules. A melting point was not observed. The new polymers, even before annealing, showed sharp X-ray diffraction patterns, evidence of semicrystallinity. The polymers, soluble in polar solvents, were analyzed by NMR in solution. Typical chemical shifts for the bisbenzoylamine protons were reported; FTIR spectra showed the characteristic imide peaks. Due to a near overlap of the carbonyl vibration of the imide group with the bisbenzoylamine carbonyl, the latter vibration was detected in only one series. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of poly(amide imide)s containing cyclohexylidene moieties with bulky substituents

Novel poly(amide imide)s (PAI) containing alkyl-substituted cyclohexylidene moieties were synthesized by conventional polycondensation of trimellitic anhydride chloride with novel aromatic diamines followed by chemical imidization using acetic anhydride and pyridine. The inherent viscosities of the resulting PAIs are relatively high and range from 71 to 112 mL g^–1. The prepared PAIs show excellent thermal stability and good solubility. The glass transition temperatures (T_g) measured by DSC are observed in the range of 312–342°C. Furthermore, all the polymers are readily soluble in less hygroscopic organic solvents like cyclohexanone, γ-butyrolactone as well as aprotic polar solvents.     

New organosoluble and thermally stable poly(urea-imide)s prepared from one-pot polyaddition reactions

A new class of aromatic poly(urea-imide)s having biphenylene pendant group was prepared by the diphenyl azidophosphate (DPAP) activated one-pot polyaddition reaction of a preformed imide ring-containing dicarboxylic acid, 4-p-biphenyl-2,6-bis(4-trimellitimidophenyl)pyridine ( 1 ) with various aromatic diamines. A model compound was also synthesized by the reaction of diimide-dicarboxylic acid 1 with two mole equivalents of aniline. In this direct method the polymers were prepared by polyaddition reactions of the in situ-formed diisocyanate with the aromatic diamines. The inherent viscosities of the polymers were measured in the range of 0.11–0.15 dL g⁻¹. The ultraviolet λ_max values of the poly(urea-imide)s were also determined. Furthermore, crystallinity of the resultant polymers was evaluated by wide-angle X-ray diffraction method, and they exhibited nearly a noncrystalline nature. All of the resulting polymers exhibited excellent solubility in common polar solvents. The glass transition temperatures of the polymers determined by DSC thermograms were in the range 241–272°C. The temperatures at 10% weight loss from their TGA curves were found to be in the range 406–437°C in nitrogen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of novel benzhydrol-containing poly(amide-imide)s

A series of novel benzhydrol-containing poly(amide-imide)s (PAIs) have been prepared from a new diimide-dicarboxylic acid, N,N′-bis(4-hydroxycarbonyl)-benzhydrol-3,3′,4,4′-tetracarboxydiimide (BHTDA-DIA), with various diamines by direct polycondensation using triphenyl phosphite and pyridine as condensing agents. The polymers obtained had inherent viscosities of 0.35–0.96 dl g⁻¹. All these PAIs, except polymer PAI-2, were soluble in N-methyl-2-pyrrolidinone and N,N-dimethylacetamide containing LiCl (1 wt%). Tough and flexible PAI films could be obtained by casting PAIs from their DMAc or NMP solutions, except for polymer PAI-2. The polymer films had a tensile strength of 93–111 MPa, an elongation at break range of 4–6%, and an initial modulus range of 2.7–3.8 GPa. The glass transition temperatures of most polymers were found to be above 255 °C. These polymers were fairly stable up to a temperature around or above 400 °C, and lost 10% weight in the range 426–507 °C in nitrogen and 423–515 °C in air. © 1999 Society of Chemical Industry     

New poly(1,3,4‐oxadiazole)s bearing pentadecyl side chains: Synthesis and characterization

The 4‐[4′‐(Hydrazinocarbonyl)phenoxy]‐2‐pentadecylbenzohydrazide was polycondensed with aromatic diacid chlorides viz., terephthalic acid chloride (TPC), isophthalic acid chloride (IPC), and a mixture of TPC : IPC (50 : 50 mol %) to obtain polyhydrazides which on subsequent cyclodehydration reaction in the presence of phosphoryl chloride yielded new poly(1,3,4‐oxadiazole)s bearing flexibilizing ether linkages and pentadecyl side chains. Inherent viscosities of polyhydrazides and poly(1,3,4‐oxadiazole)s were in the range 0.53–0.66 dL g^?1 and 0.49–0.53 dL g^?1, respectively, indicating formation of medium to reasonably high molecular weight polymers. The number average molecular weights (M_n) and polydispersities (M_w/M_n) of poly(1,3,4‐oxadiazole)s were in the range 14,660–21,370 and 2.2–2.5, respectively. Polyhydrazides and poly(1,3,4‐oxadiazole)s were soluble in polar aprotic solvents such as N,N‐dimethylacetamide, 1‐methyl‐2‐pyrrolidinone, and N,N‐dimethylformamide. Furthermore, poly(1,3,4‐oxadiazole)s were also found to be soluble in solvents such as chloroform, dichloromethane, tetrahydrofuran, pyridine, and m‐cresol. Transparent, flexible, and tough films of polyhydrazides and poly(1,3,4‐oxadiazole)s could be cast from N,N‐dimethylacetamide and chloroform solutions, respectively. Both polyhydrazides and poly(1,3,4‐oxadiazole)s were amorphous in nature and formation of layered structure was observed due to packing of pentadecyl chains. A decrease in glass transition temperature was observed both in polyhydrazides (143–166°C) and poly(1,3,4‐oxadiazole)s (90–102°C) which could be ascribed to “internal plasticization” effect of pentadecyl chains. The T₁₀ values, obtained from TG curves, for poly(1,3,4‐oxadiazole)s were in the range of 433–449°C indicating their good thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124:1281–1289, 2012     

Synthesis and characterization of aromatic/cycloaliphatic poly(amide‐ imide‐imide)s from bis(4‐amino‐ 3,5‐dimethylphenyl) cycloalkane derivatives

A series of novel aromatic diamines containing cycloaliphatic moieties was synthesized by the reaction of cycloalkanones like cyclohexanone and cycloheptanone with 2,6‐dimethylaniline. The tetrimide diacid was synthesized using the prepared diamine with 3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride/pyromellitic dianhydride and p‐aminobenzoic acid. The polymers were prepared by treating the tetrimide diacid with different aromatic diamines. The structures of the monomers and polymers were identified using elemental analysis and Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy. The polymers show excellent solubility. The polymers are amorphous and have high optical transparency. They also show good thermal stability and their T_g value is found to be in the range 268–305 °C. Copyright © 2007 Society of Chemical Industry     

Metalphthalocyanines Anchored Poly(1,3,4-oxadiazole arylene ether)s: Optical and Electrical Studies

New phenolphthalein based poly(1,3,4-oxadiazole aryl ether) (PHOP) containing side chain carboxylic acid groups derived from 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole and 2-(bis(4-hydroxyphenyl)methyl)benzoic acid have been synthesized from typical aromatic nucleophilic substitution reaction. The PHOP seizes high dielectric constant (300 at 50 Hz) by the assistance of polar pendants and its findness in advance studies needs some structure modification with high dielectric constant metalphthalocyanine (MPc, M=Co, Ni & Cu) macrocycle to come out as further enhancement of dielectric constant and become photoactive polymer embedded metalphthalocyanine (PPEMP1–9). The molecular weight of PHOP was determined by gel permeation chromatography and is found to be 33375 (M _w/M _n = 2.48). All the tailor-made polymers were well characterized by Solid State UV–Vis, thermogravimetric analysis and XRD analysis. FTIR and NMR spectroscopic techniques confirms MPc units are grafted into the polymer matrix and act as a utmost light catching materials in the visible to near IR region (400–900 nm) with remarkable drop off in optical band gap and exhibited impressive thermal properties. The variation in the AC conductivity was explained by electron hopping model and values are in the range of 3.16 × 10^?5–4.78 × 10^?5 (S/m) at 5 MHz measured at 20 °C.     

Synthesis and properties of organosoluble poly(ether imide)s containing 4,4′(octahydro-4,7-methano-5H-inden-5-ylidene) cardo group

A series of organosoluble aromatic poly(ether imide)s (PEIs) VIIa-k were synthesized from 4,4′-[(octahydro-4,7-methano-5H-inden-5-ylidene)bis(1,4-phenylene)dioxy] diphthalic dianhydride (IV) and various aromatic diamines. PEIs synthesized through two-stage polymerization had inherent viscosities of 0.51–0.64 dL/g. This series of polymers could also be synthesized from IV and diamines in a small amount of refluxing m-cresol in a one-step process and had inherent viscosities of 0.65–0.87 dL/g. For the low melting point diamines (Vj and Vk), polymers could be obtained by bulk polymerization and had inherent viscosities of 0.36 and 0.41 dL/g. Polymers showed good organosolubility and could be cast into transparent, flexible, and tough polyimide films with good tensile properties. These PEIs had glass transition temperatures among 203–281°C. Thermogravimetric analyses established that these polymers were fairly stable up to 430°C, and the 10% weight loss temperatures were recorded in the range of 473–503°C in nitrogen and 481–512°C in air atmosphere. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 987–996, 1999     

Porous poly(L‐lactic acid)/poly(ethylene glycol) blend films

Poly(L ‐lactic acid) (PLLA: M_w = 19.4 × 10⁴)/poly(ethylene glycol) (PEG: M_w = 400) blend films were formed by use of a solvent‐cast technique. The properties and structures of these blend films were investigated. The Young's modulus of the PLLA decreased from 1220 to 417 MPa with the addition of PEG 5 wt %, but the elongation at break increased from 19 to 126%. The melting point of PLLA linearly decreased with increases in the PEG content (i.e., pure PLLA: 172.5°C, PLLA/PEG = 60/40 wt %: 159.6°C). The PEG 20 wt % blend film had a porous structure. The pore diameter was 3–5 μm. The alkali hydrolysis rate of this blend film was accelerated due to its porous structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 965–970, 2004     

Synthesis and properties of new poly(amide‐imide)s based on 2,5‐bis(trimellitimido)chlorobenzene

A series of new aromatic poly(amide‐imide)s were synthesized by the triphenyl phosphite‐activated polycondensation of the diimide‐diacid, 2,5‐bis(trimellitimido)chlorobenzene (I) with various aromatic diamines in a medium consisting of N‐methyl‐2‐pyrrolidone (NMP), pyridine, and calcium chloride. The poly(amide‐imide)s had inherent viscosities of 0.76–1.42 dL g⁻¹. The diimide‐diacid monomer (I) was prepared from 2‐chloro‐p‐phenylenediamine with trimellitic anhydride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents, including NMP and N,N‐dimethylacetamide. Transparent, flexible, and tough films of these polymers could be cast from N,N‐dimethylacetamide or NMP solutions. Their cast films had tensile strengths ranging from 74 to 95 MPa, elongations at break from 7 to 11%, and initial moduli from 1.38 to 3.25 GPa. The glass transition temperatures of these polymers were in the range of 233°–260°C, and the 10% weight loss temperatures were above 450°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1691–1701, 1999     

Synthesis and antitumour activity of medium molecular weight phthalimide polymers of camptothecin

Attachment of anticancer agents to polymers has been demonstrated to improve their therapeutic profiles. A new monomer containing camptothecin, 5‐norbonene‐endo‐2,3‐dicarboxylimidoundecanoyl‐camptothecin (NDUCPT) and its homopolymer and copolymer with acrylic acid (AA) were synthesized and spectroscopically characterized. The NDUCPT content in poly(NDUCPT‐co‐AA) obtained by elemental analysis was 51%. The average molecular weights of the polymers determined by gel permeation chromatography were as follows: M_n = 12 100, M_w = 23 400 g mol^?1, M_w/M_n = 1.93 for poly(NDUCPT), M_n = 15 400, M_w = 28 300 g mol^?1, M_w/M_n = 1.83 for poly(NDUCPT‐co‐AA). The IC₅₀ value of NDUCPT and its polymers against U937 cancer cells was larger than that of CPT. The in vivo antitumour activity of all polymers in Balb/C mice bearing the sarcoma 180 tumour cell line was greater than that of CPT at a dose of 100 mg kg^?1. Copyright © 2003 Society of Chemical Industry     

Synthesis and properties of some novel,soluble and light‐coloured,aromatic poly(amide–imide) copolymers

A new type of tetraimide‐dicarboxylic acid (I) was synthesized starting from the ring‐opening addition of m‐aminobenzoic acid (m‐ABA), 4,4′‐oxydiphthalic anhydride (ODPA) and 4,4′‐methylenedianiline (MDA) at a 2:2:1 molar ratio in N‐methyl‐2‐pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of soluble and light‐coloured poly(amide–imide–imide)s (III_a–j) was prepared by triphenyl phosphite‐activated polycondensation from the tetraimide‐diacid I with various aromatic diamines (II_a–j). All films cast from DMAc had cutoff wavelengths shorter than 400 nm (376–393 nm) and had b* values between 20.46 and 40.67; these polymers were much lighter in colour than those of the corresponding trimellitimide series. All polymers were readily soluble in a variety of organic solvents such as NMP, N,N‐dimethylacetamide, dimethyl sulfoxide, and even in the less polar m‐cresol and pyridine. Compared with those of corresponding ODPA–MDA polyimide, the solubilities of poly(amide–imide–imide)s III_a–j were greatly improved. Polymers III_a–j afforded tough, transparent, and flexible films, which had tensile strengths ranging from 82 to 105 MPa, elongations at break from 8 to 14%, and initial moduli from 2.0 to 2.2 GPa. The glass transition temperature of polymers were recorded at 255–288 °C. They had 10% weight loss at a temperature above 540 °C and left more than 60% residue even at 800 °C in nitrogen. © 2002 Society of Chemical Industry     

Synthesis and characterization of poly(pyridylurea) and poly(pyridylthiourea), potentially semiconducting polymers

Poly(pyridylureas) and poly(pyridylthioureas) were synthesized by reacting 2,6‐diaminopyridine with phosgene and thiophosgene, respectively, using THF and pyridine as solvent. The synthesized polymers were characterized by IR‐spectroscopy, elemental analysis, and X‐ray photoelectron spectroscopy. Thermal stability of the polymers was determined by thermal degradation between 35°C and 700°C. The 50% weight loss of polypyridylureas was above 400°C while for the polypyridylthioureas it was above 450°C. Undoped poly(pyridylureas) and poly(pyridylthioureas) behave as semiconductors, σ = 10^?9 (Ω cm)^?1. After doping with I₂ and SbF₅, the electrical conductivity increases several orders of magnitude, σ = 10^?7(Ω cm)^?1. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of new poly(amide‐imide)s based on 1,4‐bis(trimellitimido)‐2,5‐dichlorobenzene

A series of new aromatic poly(amide‐imide)s were synthesized by the triphenyl phosphite‐activated polycondensation of the diimide‐diacid, 1,4‐bis(trimellitimido)‐2,5‐dichlorobenzene (I), with various aromatic diamines in a medium consisting of N‐methyl‐2‐pyrrolidone (NMP), pyridine, and calcium chloride. The poly(amide‐imide)s had inherent viscosities of 0.88–1.27 dL g⁻¹. The diimide‐diacid monomer (I) was prepared from 2,5‐dichloro‐p‐phenylenediamine with trimellitic anhydride. All the resulting polymers were amorphous and were readily soluble in a variety of organic solvents, including NMP and N,N‐dimethylacetamide. Transparent, flexible, and tough films of these polymers could be cast from N,N‐dimethylacetamide or NMP solutions. Cast films had tensile strengths ranging from 92 to 127 MPa, elongations at break from 4 to 24%, and initial moduli from 2.59 to 3.65 GPa. The glass transition temperatures of these polymers were in the range of 256°–317°C, and the 10% weight loss temperatures were above 430°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 271–278, 1999     

Synthesis and characterization of silicon‐containing poly(amide‐amide)s

A modified new aromatic diacid, bis[(4‐carboxyphenyl) 4‐benzamide] dimethylsilane (IV) with preformed amide linkages and a silicon moiety was synthesized and characterized by IR, NMR, mass spectroscopy, and a physical constant. Novel poly(amide‐amide)s were synthesized from IV and aromatic diamines by Yamazaki's direct polyamidation method in N‐methyl pyrrolidinone. The polymers were obtained in excellent yields and showed reduced viscosities in the range of 0.42–6.15 dL/g. They were readily soluble in aprotic polar solvents. These poly(amide‐amide)s showed glass‐transition temperatures of 303–378°C as measured by DSC and showed no weight loss below 377°C in a nitrogen atmosphere. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1610–1617, 2001     

Ru(0) complex catalyzed polyaddition New synthesis of poly(alkylenebenzoxazole) and poly(alkylenebenzimidazole)

Summary The reactions of α,ω-diyne, HC≡C(CH₂)_mC≡CH (m = 6 and 8), with 3,3'-diaminobenzidine and with 3,3'-diamino-4,4'-dihydroxybiphenyl in the presence of RU₃(CO)₁₂-PPh₃ catalyst give the corresponding poly(alkylenebenzoxazole)s and poly(alkylenebenzimidazole)s, respectively. The former polymers obtained from the equimolar reaction of the monomers are partly soluble in polar organic solvents such as DMF, DMSO, and NMP, while the poly(benzimidazole)s are soluble in these solvents. GPC measurement shows the molecular weights of the polymers, M _n of 4.8−14.1×10³ and M _w of 6.4−19.7×10³. Received: 24 November 1998/Revised version: 21 December 1998/Accepted: 24 December 1998     

Poly(amide imide)s and poly(amide imide) composite membranes by interfacial polymerization

Novel amic acid diamines (AADs) (2‐carboxyterephthalamido‐bis(alkyl or aryl amine)s, H₂N? X? NH(O?)C? C₆H₃(COOH)? C(?O)NH? X? NH₂, where X is were synthesized by reacting trimellitic anhydride chloride with aromatic or aliphatic diamines in dimethylformamide at 5–10 °C. Poly(amide imide)s (PAIs) with an amide to imide ratio of three in the polymer chains were prepared by interfacial polycondensation of the AADs in aqueous alkaline solution with isophthaloyl chloride or terephthaloyl chloride in dichloromethane at ambient temperature to form poly(amide amic acid)s, followed by their subsequent thermal cycloimidization. All of the PAIs were soluble in polar aprotic solvents such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide and N‐methylpyrrolidone, and have inherent viscosities in the range 0.15–0.48 dL g^?1. The polymers were characterized by IR and NMR spectroscopy, TGA and DSC techniques. The PAIs have initial decomposition temperatures in the range 250–460 °C in air, and glass transition temperatures of 128–320 °C, depending upon the structures of the monomers. Composite membranes containing a poly(amide amic acid) and poly(amide imide) barrier layer on the top of a porous polyethersulfone support were prepared by in situ interfacial polymerization of the AADs in aqueous alkaline solution with trimesoyl chloride in hexane, and subsequent curing. The performances of these membranes were evaluated by using aqueous feed solutions containing 2000 ppm NaCl, Na₂SO₄ or CaCl₂. Copyright © 2006 Society of Chemical Industry     

Synthesis and properties of new soluble poly(amide‐imide‐imide)s

A new‐type tetraimide‐dicarboxylic acid ( I ) was synthesized starting from the ring‐opening addition of p‐aminobenzoic acid (p‐ABA), 4,4'‐oxydiphthalic anhydride (ODPA), and 4,4'‐methylenedianiline (MDA) at a 2:2:1 molar ratio in N‐methyl‐2‐pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of poly(amide‐imide‐imide)s ( III _a‐i ) with inherent viscosities of 0.78–1.45 dL/g was prepared by triphenyl phosphite‐activated polycondensation from the tetraimide‐diacid I with various aromatic diamines ( II _a‐i ) in a medium consisting of NMP, pyridine, and calcium chloride. Most of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N‐dimethyl acetamide, dimethyl sulfoxide, and even in less polar m‐cresol. Compared with those of the corresponding poly(amideimide)s IV _a‐i , the solubilities of poly(amide‐imide‐imide)s III _a‐i were greatly improved. Polymers III _a‐h afforded tough, transparent, and flexible films, which had tensile strengths ranging from 87 to 107 MPa, elongations at break from 9% to 14%, and initial moduli from 2.0 to 2.4 GPa. The glass transition temperatures of polymers were recorded at 270°C–309°C. They had 10% weight loss at temperatures in the range of 540°C–570°C and left more than 52% residue even at 800°C in nitrogen.