Desorption of benzoic and stearic acid adsorbed upon montmorillonites: a thermogravimetric study

The desorption of benzoic acid and stearic acid from sodium and calcium montmorillonites has been studied using thermogravimetric and differential thermogravimetric analysis. Desorption of benzoic acid from sodium montmorillonites occurs at 140 °C and from calcium montmorillonites at 179 °C. This increase in temperature is attributed to the benzoic acid bonding to the calcium in the interlayer. A lowering of the dehydroxylation temperature of montmorillonites is observed with acid adsorption. Stearic acid desorbs at 218 °C as observed by the DTG curves. The desorption pattern differs between the sodium montmorillonites and the calcium montmorillonites.     

One-pot high-temperature synthesis of polyimides in molten benzoic acid: Kinetics of reactions modeling stages of polycondensation and cyclization

For aromatic and aliphatic diamines of significantly different basicities, the kinetics of acylation with phthalic anhydride in glacial acetic acid in the range 16–70°C and of imidization of corresponding bis(o-carboxyamides) in acetic acid at 140°C has been studied. The reactions under study model the stages of polycondensation and intramolecular cyclization, respectively, in the high-temperature catalytic synthesis of polyimides in molten benzoic acid. It has been established that the acylation of amino groups in acetic acid proceeds as a reversible reaction and is catalyzed by the acidic medium. The kinetic and thermodynamic parameters of the above-mentioned model reactions have been determined, and the effect of the chemical structure of diamines on these parameters has been assessed. On the basis of the experimental data obtained for the model reactions, it is inferred that, in the synthesis of polyimides in benzoic acid, the overall rate of the process is determined by the rate of the intramolecular cyclization. A low sensitivity of the cyclization reaction to a change in the structure of the starting diamines explains why high-molecular-mass polyimides can be prepared at comparable rates under these conditions from both high-and low-basicity diamines.     

New polymer syntheses. LXVI. Copolyester of 4-hydroxybenzoic acid and 3-(4'-hydroxyphenoxy)benzoic acid or 4-(3'-hydroxyphenoxy)benzoic acid

Copolyesters of 4-hydroxybenzoic acid (HBA) and 3-(4'-hydroxyphenoxy)benzoic acid were prepared by two different procedures. Either the acetyl derivatives were polycondensed in bulk at temperatures up to 300°C or they were polycondensed in an inert reactions medium (Marlotherm-S) at 340°C. Two analogous series of copolyesters were synthesized from 4-acetoxybenzoic acid (4-HBA) and 4-(3'-acetoxyphenoxy)benzoic acid. The copolyesters were characterized by elemental analyses, inherent viscosities, ¹H- and ¹³C-NMR spectroscopy, WAXS and DSC measurements, and by optical microscopy. All copolyesters synthesized in solution were highly crystalline materials which were neither meltable nor soluble. Part of the copolyesters prepared by polycondensation in bulk were semi-crystalline, meltable, and soluble. The copolyester derived from 3-(4'-hydroxyphenoxy)benzoic acid proved to be thermotropic forming a nematic melt, whereas the isomeric copolyesters of 4-(3'-hydroxyphenoxy)benzoic acid only formed isotropic melts. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of poly[4-(4-hydroxyphenoxy) benzoic acid]

Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc.     

Some aspects of polybenzimidazoles’ synthesis in Eaton reagent under different temperatures and microwave irradiation

Solution polycondensations of 3,3′-diaminobenzidine with two dicarboxylic acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid) to obtain two different polybenzimidazoles, OPBI and CF₃PBI, correspondingly, were studied in terms of formation of processable polymers and insoluble crosslinked gel. The syntheses were conducted in Eaton’s reagent using conventional heating (CH) at 100, 140 and 180?°C and microwave irradiation (MW) at 90 and 100?°C. The content of gel fraction was lesser using high temperature conditions under CH. The MW-assisted syntheses resulted in acceleration of polycondensations, but an abrupt growth of the insoluble gel was also observed under these conditions. The FTIR data showed that MW irradiation stimulated the side acylation reactions, and OPBI suffered more from the side acylation than CF₃PBI.     

Synthesis and characterization of novel hyperbranched polybenzimidazoles based on an AB2 monomer containing four amino groups and one carboxylic group

A new kind of AB₂ monomer, 4‐[2,6‐bis(3,4‐diaminophenyl)pyridin‐4‐yl]benzoic acid, was synthesized, and several hyperbranched polybenzimidazoles (HPBIs) were prepared through self‐polymerization followed by modification reactions with end‐capping reagents such as 4‐methyl benzoic acid and 3‐[3,5‐bis(trifluoromethyl)phenoxy] benzoic acid. The HPBIs had good solubility in strongly aprotic solvents, such as N‐methyl‐2‐pyrrolidone, N,N′‐dimethylformamide, N,N′‐dimethylacetamide, and dimethyl sulfoxide. They also exhibited excellent thermal properties, with glass‐transition temperatures of 318–381 °C and 10% weight loss in the range of 338–674 °C in nitrogen and 329–509 °C in air. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5729–5739, 2006     

Thermal degradation of aramids: Part I—Pyrolysis/gas chromatography/mass spectrometry of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of poly(1,3-phenylene isophthalamide) or Nomex (I) and poly(1,4-phenylene terephthalamide) or Kevlar (II) aramids have been investigated in the temperature range 300–700°C by pyrolysis/gas chromatography/mass spectrometry. The initial degradation products below 400°C of (I) are carbon dioxide and water. At 400°C benzoic acid and 1,3-phenylenediamine are detected. Benzonitrile, aniline, benzanilide, N-(3-aminophenyl)benzamide as well as carbon monoxide and benzene are evolved in the range 430–450°C. The yields of these products increase rapidly in the range 450–550°C. Isophthalonitrile is observed at 475°C and hydrogen cyanide is detected above 550°C, as are other secondary products such as toluene, tolunitrile, biphenyl, 3-cyanobiphenyl and 3-aminobiphenyl. Pyrolysis of (II) below 500°C evolves only water and trace amounts of carbon dioxide. At 520–540°C the following degradation products have been detected: 1,4-phenylenediamine, benzonitrile, aniline, benzanilide and N-(4-aminophenyl)benzamide. These products as well as carbon dioxide and water increase appreciably between 550°C and 580°C; benzoic acid, terephthalonitrile, benzene and 4-cyanoaniline are also detected in this temperature range. Above 590°C, hydrogen, carbon monoxide, hydrogen cyanide, toluene, tolunitrile, biphenyl, 4-aminobiphenyl and 4-cyanobiphenyl are evolved. Degradation reactions consistent with the formation of these products, which involve initial heterolytic cleavage of the amide linkage for (I) and initial homolytic cleavage of the aromatic NH and amide bonds for (II), are described.     

Synthesis of linear and hyperbranched poly(etherketone)s containing flexible oxyethylene spacers

As an alternative to strong acid reaction media for the Friedel–Crafts acylation for a polymer‐forming reaction, a mild polyphosphoric acid (PPA) with optimized amount of phosphorous pentoxide (P₂O₅) has been tested for the polymerization of AB monomers 4‐(2‐phenoxyethoxy)benzoic acid and 3‐(2‐phenoxyethoxy)benzoic acid, and an AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid. The reaction progress of AB₂ monomer was conveniently traced by FTIR spectroscopy monitoring aromatic ketone (C?O) stretching bands arisen from carboxylic acid groups at the chain ends and carbonyl groups in the backbone as a function of reaction time at 110 °C. The resultant linear and hyperbranched polymers containing flexible oxyethylene spacers, which were prone to be hydrolyzed in strong acids at elevated temperature, displayed high intrinsic viscosities. Thus, the reaction medium PPA/P₂O₅ mixture as an electrophilic substitution reaction was indeed benign not to depolymerize growing polymer molecules but strong enough for the direct generation of carbonium ion from carboxylic acid to promote efficient polymerization. The resultant hyperbranched poly(etherketone) (PEK) displayed the best solubility among samples. All PEKs showed good thermal stability; glass transition temperatures were in the range of 90–117 °C; 5% weight loss generally occurred at greater than 345 °C in air. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5112–5122, 2007     

One‐pot preparation of aromatic poly(azomethine ester) fibrillar crystals using reaction‐Induced crystallization

Polymerizations of 4‐(4‐acetoxybenzylideneamino)benzoic acid were performed in dibenzyltoluene (DBT) and a mixture of DBT and liquid paraffin at 350 °C for 6 h. Fibrillar crystals of poly[4‐(4‐oxybenzylideneamino)benzoyl] (POAB) having the width of 50–450 nm and the length of over 15 μm were obtained by the crystallization during the polymerization. The fibrillar crystals possessed high crystallinity and the molecular chains aligned perpendicular to the long axis of the fibrillar crystals. Plate‐like crystals were initially formed by the crystallization of oligomers, and then they changed to the fibrillar crystals via the formation of bundle‐like crystals after 1 h. Molecular weight increased by the further polymerization in the crystals. Based on these results, one‐pot preparation of the fibrillar POAB crystals was examined by the polymerization of 4‐acetoxybenzaldehyde and 4‐aminobenzoic acid. The polymerization at 180 °C for 2 h and then at 350 °C for 6 h afforded the fibrillar crystals with a small amount of the ribbon‐like crystals. Although the side‐reaction to generate the p‐benzamide sequences was not completely depressed, the sequence of heating in which 180 °C for the formation of the azomethine linkage and then 350 °C for the formation of the ester linkage was preferable to prepare the fibrillar POAB crystals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of reactive three‐arm star‐shaped oligoimides with narrow molecular weight distribution

Series of star‐shaped three arms oligoimides (SOI) with terminal amino groups with narrow MWD ((M_w/M_n = 1.1–2) was synthesized by the one‐stage high‐temperature polycondensation in molten benzoic acid at 140 °C. The (B3+AB′) approach with the “slow addition of monomer” method was used for this synthesis, where B3 is 2,4,6‐tris(4‐aminophenoxy)toluene and AB′ is 3‐aminophenoxy phthalic acid. The SOI arm's length was controlled by the AB′/B3 mole ratio of 10:1, 20:1, 40:1, and 100:1. By the reaction of SOI's terminal amino groups with acetic anhydride, corresponding acetamide derivatives were obtained. SOI synthesized are soluble in selected organic solvents. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2004–2009     

Preparation of amphiphilic networks by Diels-Alder reactions between oligo(butyl methacrylate) with furan end-groups and a poly(ethylene oxide-co-acetylenedicarboxylate)

A butyl methacrylate oligomer with furan end-groups was synthesized by ozonolysing a poly(butyl methacrylate-co-butadiene) latex. The end-groups of this oligomer were amidated with aminomethylfuran to give a coagulated mass of derivatized oligomers. This furan functional oligomer was then mixed with poly(ethylene oxide-co-acetylenedicarboxylate) and heated at 60°C or 125°C. The material cured at 125°C was found to contain a higher gel fraction (55 wt.-%) than that cured at 60°C (30 wt.-%).     

All‐aromatic liquid crystalline thermosets with high glass transition temperatures

We have synthesized and characterized a new family of low melting all‐aromatic ester‐based liquid crystal oligomers end‐capped with reactive phenylethynyl end groups. In a consecutive, high‐temperature step, the reactive end groups were thermally activated and polymerization was initiated. This reactive oligomer approach allows us to synthesize liquid crystal thermosets with outstanding mechanical and thermal properties, which are superior to well‐known high‐performance polymers such as PPS and PEEK. We have modified an intractable LC formulation based on hydroquinone and terephthalic acid, with M_n = 1000, 5000, and 9000 g mol^?1, and varied the backbone composition using isophthalic acid, resorcinol, 4‐hydroxy‐benzoic acid, 6‐hydroxy‐2‐naphthoic acid, and chlorohydroquinone. All fully cured polymers showed glass transition temperatures in the range of 164–275 °C, and high storage moduli at room temperature (～ 5 GPa) and elevated temperature (～ 2 GPa at 200 °C). All oligomers display nematic mesophases and in most cases, the nematic order is maintained after cure. Rheology experiments showed that the phenylethynyl end group undergoes predominantly chain extension below 340 °C and crosslinking above this temperature. Highly aligned fibers could be spun from the nematic melt, and we found that the order parameter 〈P₂〉 was not affected by the chain extension and crosslink chemistry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1368–1380, 2009     

Enzymatic oxidative polymerization of para‐imine functionalized phenol catalyzed by horseradish peroxidase

Enzymatic oxidative polymerization of a new para‐imine functionalized phenol derivative, 4‐(4‐hydroxybenzylideneamino)benzoic acid (HBBA), using horseradish peroxidase enzyme and hydrogen peroxide oxidizer has been investigated in an equivolume mixture of an organic solvent (acetone, methanol, ethanol, dimethylformamide, 1,4‐dioxane, and tetrahydrofuran) and phosphate buffer (pH = 5.0, 6.0, 6.8, 7.0, 7.2, 8.0, and 9.0) at different temperatures under air for 24 h. The resulting oligomer, oligo(4‐(4‐hydroxybenzylideneamino)benzoic acid) [oligo(HBBA)], was characterized using ultraviolet–visible, Fourier transform infrared (FT‐IR), ¹H nuclear magnetic resonance (NMR), cyclic voltammetry, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analyses. Polymerization involved carbon dioxide and hydrogen elimination from the monomer, and terminal units of the oligomer structure consisted of phenolic hydroxyl (–OH) groups at the ends. The polymer is mainly composed of a mixture of phenylene and oxyphenylene units according to ¹H NMR and FT‐IR analyses. Effects of solvent system, temperature and buffer pH on the polymerization have been investigated in respect to the yield and molecular weight (M_n) of the product. The best condition in terms of the highest molecular weight (M_n = 3000 g/mol, DP ~ 15) was achieved in an equivolume mixture of 1,4‐dioxane/pH 5.0 phosphate buffer condition at 35°C. Electrochemical characterization of oligo(HBBA) was investigated at different scan rates. The resulting oligomer has also shown relatively high thermal stability according to thermogravimetric analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Rational construction of self-assembly azobenzene derivative monolayers with photoswitchable surface properties

hoto-responsive azobenzene (ABZ) derivatives with different end groups (R) were employed to construct selfassembled monolayers (SAMs) on silicon substrates. The SAMs based on hydrophilic (4-(4'-aminophenylazo) benzoic acid, ABZ-COOH) show excellent reversible photoswitching performance with a large contact angle change of 35° under optimized process.     

Benzopyridosilaazepines and benzopyridosilaazepinones

The Beckmann rearrangement of dihydrosilazatone oximes yields benzopyridosilaazepinones which are isomeric relative to the position of the amide fragment in the central ring. One of these isomers is converted upon thermolysis at 250 °C to the lactam of o-(3-aminopyridyl-4)benzoic acid. The reduction of benzopyridosilaazepinones yields benzopyridosilaazepines.     

New polymer syntheses 16. LC-copolyesters of 3-(4-hydroxyphenyl) propionic acid and 4-hydroxy benzoic acids

The polycondensation of 3-(4-hydroxy phenyl)-propionic acid, 4-Hypp, by means of acetanhydride or acetylchloride was conducted either in the presence or in the absence of a liquid reaction medium. DSC measurements, polarizing microscope, and X-ray diffraction studies indicate poly(4-Hypp) possesses at about 215°C a reversible first order transition between two solid phases. Copolyesters containing various mole ratios of 4-Hypp and 4-hydroxy benzoic acid, 4-Hybe, were prepared by bulk condensation with acetanhydride at 320°C. At 4-Hypp/4-Hybe ratios less than 1.0:1.5 the reaction product was heterogeneous, containing crystals of pure poly(4-Hybe). Neither increasing the reaction time nor the variation of the transesterification catalyst resulted in an entirely homogeneous copolyester. However, for 4-Hypp/4-Hybe ratios greater than 1.0:1.5, ¹³C NMR spectra indicate perfectly random sequences. Also, terpolyesters containing 3-chloro-4-hydroxy- or 3,5-dichloro-4-hydroxy-benzoic acid were heterogeneous with less than 30 mol % 4-Hypp. DSC measurements revealed for all polyesters a glass transition in the range of 55–78°C. Temperature dependent X-ray diffraction studies confirm that the solid phase is a s.c. LC-glss. Correspondingly low heat distortion temperatures were found by thermomechanical analyses. The copolyesters display under the polarizing microscope LC-phase up to temperatures of 450–480°C, where rapid thermal degradation prevents further investigations. In the case of the 4-Hypp/4-Hybe 1:1 copolyester, the LC-phase extends over a temperature range of about 400°C. TGA measurements indicate beginning thermal degradation at temperatures between 350 and 380°C.     

Chemoenzymatic polymerization of hydrazone functionalized phenol

Hydrazone substituted oligophenol was synthesized via enzymatic oxidative polymerization of (E)-2-((2-phenylhydrazono)methyl)phenol. Enzymatic polymerization catalyzed by Horseradish peroxidase (HRP) enzyme and H₂O₂ oxidizer yielded oligophenol with hydrazone functionality on the side-chain. Effects of various factors including solvent system, reaction pH and temperature on the polymerization were studied. Optimum polymerization conditions with the highest yield (84%) and molecular weight (M_n = 8 × 10³, DP ≈ 37, PDI = 1.11) was achieved using MeOH/pH 6.0 buffer (1: 1 vol %) at 25°C in 24 h under air. Synthesized oligomer was characterized by ¹H and ¹³C NMR, FTIR, UV–Vis spectroscopy, GPC, cyclic voltammetry and thermogravimetric analyses. The polymerization involved hydrogen elimination from the monomer, and terminal units of the oligomer structure consisted of phenolic hydroxyl (–OH) end groups. The oligomer backbone possessed phenylene and oxyphenylene repeat units. The resulting oligomer was completely soluble in common organic solvents. The oligomer was thermally robust and exhibited 5% mass loss at 375°C and 50% mass loss at 440°C.     

Kinetics of bulk polymerization of trimeric phosphonitrilic chloride

The kinetics of the pure bulk polymerization of trimeric phosphonitrilic chloride were investigated in the temperature range 240–255°C. The reaction was found to be secondorder with an activation energy of 57 kcal./mole. Polymerization catalyzed by benzoic acid was first-order, and the reactivities of benzoic acid and sodium benzoate at 235°C. were found to be about similar. The volatile decomposition products for the benzoic acid reaction were identified. Mechanisms are postulated for the catalyzed and uncatalyzed reactions.     

Molecular and crystalline structure of pyrocatechol and hydroquinone dimethacrylates and their reactivity in melts

X-ray diffraction analysis of pyrocatechol and hydroquinone dimethacrylates (T _m = 18 and 86–88°C, respectively) shows that the oligomer molecules within crystals are packed in stacks where the methacrylate fragments of neighboring molecules are parallel to each other. The minimum distances between the centers of double bonds of adjacent methacrylate fragments in crystals of pyrocatechol and hydroquinone dimethacrylates are 4.621(3) and 4.269(4) Å. The curves showing the reduced rate of photopolymerization of oligomer melts versus conversion (9,10-phenanthrenequinone used as the initiator) display a maximum at conversions of 1.5–3.0%. The limiting conversion in photopolymerization of molten pyrocatechol dimethacrylate at 25 and 40°C is 20%; for hydroquinone dimethacrylate at 95°C, it is approximately 10%. As the temperature rises from 25 to 40°C, the maximum reduced rate of photopolymerization of pyrocatechol dimethacrylate increases by a factor of 1.4.     

Photogeneration of polyfunctional amines and novel thermal curing reactions of epoxy resin and polyurethane oligomer using these amines

Photochemical reactions of various blocked polyfunctional amines such as bis(4-formylaminophenyl)methane (FAPM), bis(4-acetylaminophenyl)methane (AAPM), bis(4-benzoylaminophenyl)methane (BAPM), 2,4-diformylaminotoluene (DFAT), m-xylene diformamide, and bis[[(2-nitrobenzyl)oxy]carbonyl]hexane-1.6-diamine were carried out to give the corresponding free amines in THF solution, in epoxy resin, or in polyurethane oligomer with terminal isocyanate groups. Photolysis of FAPM and DFAT to produce the corresponding polyfunctional amines such as 4,4'-methylenedianiline and 2,4-diaminotoluene proceeded with 80 and 75% conversions, respectively, in THF solution under UV irradiation at 5 h. AAPM and BAPM also produced the corresponding photo-Fries rearrangement products with 32 and 38% conversions, respectively, under the same irradiation conditions. The photolysis of those compounds also occurred with similar conversions in the epoxy resin and in the polyurethane oligomer under UV irradiation; and the thermal curing reactions of the epoxy resin and the polyurethane oligomer with photogenerated polyfunctional amines proceeded smoothly after heating at 140°C for 2 hrs. © 1993 John Wiley & Sons, Inc.