Preparation and properties of imide‐containing elastic polymers from elastic polyureas and pyromellitic dianhydride

A new approach to obtain imide‐containing elastic polymers (IEPs) via elastic and high‐molecular‐weight polyureas, which were prepared from α‐(4‐aminobenzoyl)‐ω‐[(4‐aminobenzoyl)oxy]‐poly(oxytetramethylene) and the conventional diisocyanates such as tolylene‐2,4‐diisocyanate(2,4‐TDI), tolylene‐2,6‐diisocyanate(2,6‐TDI), and 4,4′‐diphenylmethanediisocyanate (MDI), was investigated. IEP solutions were prepared in high yield by the reaction of the polyureas with pyromellitic dianhydride in N‐methyl‐2‐pyrrolidone (NMP) at 165°C for 3.7–5.2 h. IEPs were obtained by the thermal treatment at 200°C for 4 h in vacuo after NMP was evaporated from the resulting IEP solutions. We assumed a mechanism of the reaction via N‐acylurea from the identification of imide linkage and amid acid group in IEP solutions. NMR and FTIR analyses confirmed that IEPs were segmented polymers composed of imide hard segment and poly(tetramethylene oxide) (PTMO) soft segment. The dynamic mechanical and thermal analyses indicated that the IEPs prepared from 2,6‐TDI and MDI showed a glass‐transition temperature (T_g ) at about −60°C, corresponding to T_g of PTMO segment, and suggested that microphase‐separation between the imide segment and the PTMO segment occured in them. TGA studies indicated the 10% weight‐loss temperatures (T₁₀) under air for IEPs were in the temperature range of 343–374°C. IEPs prepared from 2,6‐TDI and MDI showed excellent tensile properties and good solvent resistance. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 715–723, 2000     

High performance heteroaromatic poly(azo-ester)s and their miscible blends: Thermomechanical and conductivity profile

An interesting type of thermally stable and processable poly(azo-ester)s (PAEs) have been synthesized through the polycondensation of a novel diol—(E)-1-(5-(3-hydroxypyridylazo)thiocarbamoyl-aminonaphthyl)-3-(3-hydroxypyridylazo)thiourea, and various diacid chlorides. The dihydroxy compound containing azo group (?N=N?) was prepared via multi-step procedure in which the coupling of bisthiourea compound with diazonium chloride (in alkali) yielded the desired monomer. The polymeric materials were characterized in terms of FTIR, ¹H NMR, solubility, solution viscosity, molecular weight, electrical conductivity, glass transition and thermal degradation temperatures. PAEs possessed high inherent viscosity 1.19–1.23 dL/g and molar mass (8.3–8.5) × 10⁴. The polymers were thermally stable in the range 531–541°C (10% gravimetric loss T ₁₀) having T _g′ = 258–266°C. PAEs were, thus, melt blended with polyaniline resulting in high performance materials that potentially combined the fine thermal properties and processability of poly(azo-ester)s with electrical characteristics of polyaniline. The miscible blends exhibited good heat stability (T ₁₀ = 525–527°C, T _g = 246–252°C) and mechanical strength (61.81–63.19 MPa) compared with several polyaniline-based blends. FESEM showed nano-level homogeneity of the microstructure liable for better electrical conductivity (3.2–4.2 S/cm).     

Synthesis of aromatic amine curing agent containing non-coplanar rigid moieties and its curing kinetics with epoxy resin

A kind of aromatic diamine, 4′, 4″-(2, 2-diphenylethene-1, 1-diyl)dibiphenyl-4-amine (TPEDA), was successfully synthesized via Suzuki coupling reaction. The TPEDA containing nonplanar rigid moieties can be used as epoxy resins curing agent to improve the complex properties of cured composites. The curing kinetics during thermal processing of E51/TPEDA system was investigated by nonisothermal differential scanning calorimeter. The average activation energy (E _α), pre-exponential factor (lnA), and reaction order (n) calculated from the Kissinger, the Ozawa, the Friedman and the Flynn–Wall–Ozawa methods were 55.8 kJ mol^?1, 9.4 s^?1 and 1.1, respectively. By the aid of estimated kinetic parameters, the predicted heat generation vs temperature curves fit well with the experimental data, which supported the validity of the estimated parameters and the applicability of the analysis method used in this work. By the introduction of nonplanar rigid moieties, the cured epoxy resins with TPEDA exhibited a higher glass transition temperature (T _g = 258 °C), good thermal stability (≈395 °C at 10 % mass-loss), and high char yield (36.6 % at 700 °C under nitrogen) compared with conventional curing agents.     

Synthesis and properties of thermoplastic polyimides with ether and ketone moieties

A series of polyimides containing ether and ketone moieties were synthesized from 1,3‐bis(4‐fluorobenzoyl) benzene and several commercially available dianhydrides via a conventional two‐step polymerization. The inherent viscosities of Polyamide acids ranged from 0.46 to 0.73 dL/g. Thermal properties, mechanical properties, and thermalplasticity of the obtained polimide films were investigated by focusing on the chemical structures of their repeat units. These films were amorphous, flexible, and transparent. All films displayed low T_gs (184–225 °C) but also excellent thermal stability, the 5% weight loss temperature was up to 542 °C under nitrogen. The films showed outstanding mechanical properties with the modulus up to 3.0 GPa and the elongation at break in the range of 8–160%. The uniaxial stretching of PI‐a at high temperature was studied owing to its excellent flexibility. The PI‐a had an elongation at break up to 1600% at 245 °C and the uniaxially stretched film exhibited a much higher modulus (3.9 GPa) and strength (240 MPa) than undrawn film. The results indicated that PI‐a can potentially be used to prepare materials such as fiber, ultra‐thin film or ultra‐high modulus film. All the obtained films also demonstrated excellent thermoplasticity (drop of E′ at T_g > 10³) which made the polyimides more suitable for melt processing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2878–2884, 2010     

Preparation,characterization, and properties of poly(thioether ether imide)s from isomeric bis(chlorophthalimide)s and 4,4′‐thiobisbenzenethiol

A series of isomeric poly(thioether ether imide)s (PTEIs) containing both thioether and ether linkages were prepared by nucleophilic substitution reaction of isomeric bis(chlorophthalimide)s with 4,4′‐thiobisbenzenethiol. The inherent viscosities of these polymers were in the range of 0.40–0.56 dL/g in m‐cresol at 30°C. The T_g values of PTEIs were 196–236°C; T_5% values reached up to 509–529°C in nitrogen and 508–534°C in air, which indicated this kind of polyimide possessed excellent thermal stability. The hydrolytic stability was arranged in the order: a > b > c > d > e, and improved with increasing the content of 3‐substituted phthalimide unit in the polymer backbone. Flexible films could be cast from the polymer solution with a solid content of 10%. The PTEI films exhibited good mechanical properties with tensile strengths of 90–104 MPa, elongations at break of 6.6–7.9%, and tensile moduli of 2.3–2.6 GPa. The minimum complex viscosity of PTEIs c was about 100 Pa·s at 310°C and the minimum melt viscosity of PTEIs (a–e) decreased with increasing the content of unsymmetrical 3,4′‐substituted phthalimide units. Copyright © 2014 John Wiley & Sons, Ltd.     

Benzocyclobutene in polymer synthesis. III. Heat-resistant thermosets based on Diels–Alder polymerization of a bisbenzocyclobutene and a bismaleimide

Several compatible mixtures of 2,2-bis[4-(N-4-benzocyclobutenyl) phthalimid-4-phenyl]hexafluoropropane (BCB) and 1,1′-(methylene di-4,1-phenylene)bismaleimide (BMI) were prepared according to the molar ratios (BCB : BMI): 1 : 1; 1 : 1.5; 1 : 3; 1.5 : 1. Complete compatibility of the mixtures was evidenced by a single initial T_g. All mixtures showed relatively low initial T_g's (61–70°C) and characteristic polymerization exotherms of benzocyclobutene-based systems (onset: 221–225°C; maximum: 257–259°C), providing an excellent processing window (ca. 155°C). The cured sample of the mixtures, pure BCB and BMI (250°C; N₂; 8 h) were subjected to comparative isothermal gravimetric analysis (ITGA). After 200 h at 650°F (343°C) in circulating air, the cured BMI sample retained only 3% of its original weight, whereas the mixtures of BCB and BMI exhibited thermo-oxidative stabilities similar to BCB (13–15% weight loss). A model compound was synthesized from the intimate mixture of N-phenylmaleimide and N-benzocyclobutenyl phthalimide in 63% yield. The ITGA results and isolation of the model Diels–Alder adduct render strong support to the conviction that Diels–Alder polymerization is indeed the predominant curing process in the BCB/BMI system.     

Thermal runaway reaction evaluation of two by-products mixed with cumene hydroperoxide in the oxidation tower

Oxygen (O₂) or air is widely used to produce cumene hydroperoxide (CHP) in the cumene oxidation tower. The aim of this study was applied to analyze thermal hazard of two by-products including alpha-methylstyrene (AMS) and acetophenone (AP) in a CHP oxidation tower. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were operated to evaluate thermal runaway reaction of CHP mixed with AMS and AP. Exothermic onset temperature (T ₀), maximum temperature (T _max), activation energy (E _a), etc., that were employed to prevent and protect thermal runaway reaction and explosion in the manufacturing process and storage area. In view of proactive loss prevention, the inherently safer handling procedure and storage situation should be maintained in the chemical industries. The T ₀ of 30 mass% CHP was determined to be 105 °C by DSC. Therefore, the T ₀ of 30 mass% CHP mixed with AMS was determined to be 60–70 °C by DSC. The exothermic reaction of CHP/AP and CHP/AMS by DSC under N₂ reaction gas is thermal decomposition of oxygen–oxygen bond (–O–O–) because of the anaerobic reaction.     

Benzocyclobutene in polymer synthesis. I. Homopolymerization of bisbenzocyclobutene aromatic imides to form high-temperature resistant thermosetting resins

A series of new bisbenzocyclobutene-terminated aromatic imide monomers has been synthesized from the condensation reaction of 4-aminobenzocyclobutene and the perspective dianhydride in refluxing acetic acid/toluene. The differential scanning calorimetric studies of the foregoing monomers indicated that polymerization exotherms began at 229–250°C and reached their maxima at 258–263°C. The cured samples (250–254°C; N₂; 8 h) were surprisingly stable toward thermo-oxidative degradation; only 7–10% weight loss was observed after 200 h (in air) at 314°C (600°F). At higher temperatures (650 and 700°F), the most rigid structure was the most thermo-oxidatively stable. An approach to enhance both the final glass-transition temperature (T_g cure) and the thermo-oxidative stability of the bisbenzocyclobutene system was to dilute the cure-site density since the cure-site structure is the weakest part of the polymeric structure. Therefore, a series of bisbenzocyclobutene-terminated aromatic imide oligomers were prepared, using various aromatic amines as the chain-extending agents. Meta-phenylenediamine was apparently the most effective in the advancement of both the T_g (cure) and thermo-oxidative stability.     

New light‐colored poly(ether imide)s based on 2,5‐di‐tert‐butylhydroquinone bis(ether anhydride) and aromatic diamines

A series of poly(ether imide)s (PEIs), III _a–k , with light color and good physical properties were prepared from 1,4‐bis(3,4‐dicarboxypheoxy)‐2,5‐di‐tert‐butylbenzene dianhydride ( I ) with various aromatic diamines ( II _a–k ) via a conventional two‐stage procedure that included a ring‐opening polyaddition to yield poly(amic acid)s (PAA), followed by thermal imidization to the PEI. The intermediate PAA had inherent viscosities in the range of 1.00–1.53 dL g^?1. Most of the PEIs showed excellent solubility in chlorinated solvents such as dichloromethane, chloroform, and m‐cresol, but did not easily dissolve in dimethyl sulfoxide and amide‐type polar solvents. The III series had tensile strengths of 96–116 MPa, an elongation at break of 7–8%, and initial moduli of 2.0–2.5 GPa. The glass‐transition temperatures (T_g) and softening temperatures (T_s's) of the III series were recorded between 232 and 285 °C and 216–279 °C, respectively. The decomposition temperatures for 10% weight loss all occurred above 511 °C in nitrogen and 487 °C in air. The III series showed low dielectric constants (2.71–3.54 at 1 MHz), low moisture absorption (0.18–0.66 wt %), and was light‐colored with a cutoff wavelength below 380 nm and a low yellow index (b^*) values of 7.3–14.8. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1270–1284, 2005     

Water splitting as a tool for obtaining insight into metal–support interactions in catalysis

This review is focused on the use of the water splitting reaction for characterizing oxygen vacancies in supported metal catalysts and more generally to get insight into the high-temperature modifications of metal–support interactions. Three supports widely used in catalysis are considered, namely alumina, silica and ceria. The catalysts were reduced at temperatures T_R ranging from 200 to 1000 °C. The reaction with water was carried out at temperatures T_OX ranging from 100 to 1000 °C. In every case, the metal (Rh or Pt) was chosen among those which are not oxidizable by water. Extensive investigations of the reactivity of water with unsupported metals and films confirmed this choice. The reaction is then selective for the titration of O vacancies, generally associated with reduced cations of the support. On alumina-supported catalysts, reduction at T_R > 600 °C leads to the formation of oxygen vacancies strictly confined to the periphery of metal particles. The amount of hydrogen produced Q_H is coherent with the peripheral oxygen density. Reduction of silica-supported catalysts at T_R > 600 °C generates metal silicides that can be selectively destroyed by water with reformation of silica and metal nanoparticles. Oxygen vacancies are formed on ceria catalysts at 200 °C. These oxygen vacancies are confined to the surface up to 600 °C. At higher temperatures, oxygen vacancies are formed in the bulk: about 50% of CeO₂ would be reduced at 900 °C. The amount of H₂ produced by reaction with water is thus very high on metal-ceria catalysts. At T_R > 900 °C, metal cerides start to form. Remarkably, a significant reactivity of H₂O on a Rh/CeO₂ catalyst reduced at 850 °C is recorded as of 100 °C. However, the quantitative titration of oxygen vacancies required temperatures T_OX > 500 °C. As a rule, the technique of water splitting allows the detection of 1 μmol g⁻¹ of oxygen vacancies, i.e. a few 0.1% of the surface in the case of reducible oxides of 10–20 m² g⁻¹.     

DSC study on the thermal properties of soybean protein isolates/corn starch mixture

The use of soybean protein isolates (SPI) and corn starch (CS) for the manufacturing of textured protein by thermo-mechanical means requires a characterization of their thermal properties. SPI and CS mixtures were examined at starch mass fractions from 0 (pure SPI) to 100 (pure CS). The blends were determined by means of differential scanning calorimetry, with water content of 30, 50, and 70 % and heating rate of 5 and 10 °C min^?1 over 20 to 130 °C. The results obtained showed that protein in the blend increased the onset (T _o) and peak (T _p) temperatures of the starch gelatinization, while starch in the blend decreased the ΔH and ΔT_1/2 of the protein. T _o , T _p, and ΔT_1/2 of SPI and CS decreased significantly with the increase of water content. T _p and ΔT_1/2 of SPI and CS had a marked increase with an increase of heating rate from 5 to 10 °C min^?1. These results suggested that there was no chemical reaction between SPI and CS when they were heated from 20 to 130 °C. SPI in the blend restricted the CS gelatinization, while the presence of CS protected the SPI from denaturation. The increasing water content did promote thermal transition of the mixture. Higher heating rate leads to higher transition temperature.     

Performance of high-temperature thermosetting polyimide composites modified with thermoplastic polyimide

The preparation of polyimide (PI) resin with high heat resistance and toughness is a significant challenge. In this study, thermoplastic PI (TPI) was used to toughen thermosetting PIs, and toughened PI (TPI/PI) blends were prepared. The modified PI resin system exhibited good thermal stability, excellent heat resistance, and high toughness. The results indicated that the TPI/PI blends maintained the curing behavior and characteristics of the PI oligomer. The T_g of the cured TPI/PI blend exceeded 395 °C, and the T_5% values were in the range of 533–563 °C, suggesting excellent thermal stability and heat resistance. The maximum impact strength was increased by 46% compared with that of pure PI, indicating the excellent toughening effect of the TPI. Carbon fiber-reinforced PI composites were prepared using the toughening system as a matrix. The compression-after-impact values of the carbon fiber-reinforced PI composites were up to 190 MPa, indicating the excellent toughness of the materials.     

Partially biobased polymers: The synthesis of polysilylethers via dehydrocoupling catalyzed by an anionic iridium complex

Partially biobased polysilylethers (PSEs) are synthesized via dehydrocoupling polymerization catalyzed by an anionic iridium complex. Different types (AB type or AA and BB type) of monomers are suitable. Levulinic acid (LA) and succinic acid (SA) have been ranked within the top 10 chemicals derived from biomass. BB type monomers (diols) derived from LA and SA have been applied to the synthesis of PSEs. The polymerization reactions employ an air-stable anionic iridium complex bearing a functional bipyridonate ligand as catalyst. Moderate to high yields of polymers with number-average molecular weights (M_n) up to 4.38 × 10⁴ were obtained. A possible catalytic cycle via an Ir-H species is presented. Based on the results of kinetic experiments, apparent activation energy of polymerization in the temperature range of 0–10 °C is about 38.6 kJ/mol. The PSEs synthesized from AA and BB type monomers possess good thermal stability (T₅ = 418 °C to 437 °C) and low glass-transition temperature (T_g = −49.6 °C).     

Synthesis of a poly(vinyl ether) containing a benzocyclobutene moiety and its reaction with dienophiles

1‐Benzocyclobutenyl vinyl ether (1) was easily prepared by the elimination reaction of hydrogen bromide from 1‐benzocyclobutenyl 1‐bromoethyl ether obtained by 1‐bromobenzocyclobutene and ethylene glycol via two steps in a good yield. Cationic polymerizations of 1 was carried out at −78°C for 2 h in toluene in the presence of BF₃OEt₂ as an initiator to give quantitatively the corresponding polymers (2) as white solids. As a model reaction of the polymer reaction of 2 with dienophiles, the Diels–Alder reactions of 1‐methoxybenzocyclobutene with maleic anhydride (MA) in toluene at 100–140°C for 3 h were carried out to obtain the corresponding Diels–Alder adduct quantitatively at 140°C. The polymer reactions of 2 with MA and N‐phenylmaleimide (MI) in toluene were carried out to yield the corresponding Diels–Alder adduct polymers in good yields. The degree of introduction of the dienophile could be controlled by temperature, and the unreacted benzocyclobutene moiety could further react with another benzocyclobutene moiety or dienophile. The properties (solubilities, T_g, and temperature of 10% weight loss) of the polymers obtained from the polymer reaction were quite different from those of 2. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 59–67, 1999     

Synthesis,characterization and thermal stability of new dumbbell-shaped isobutyl-substituted POSSs linked by aromatic bridges

Five new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R₇(SiO_1.5)₈ (with R = isobutyl), linked to various aromatic bridges (Ar, Ar–Ar, Ar–O–Ar, Ar–S–Ar and Ar–SO₂–Ar, where Ar = p-C₆H₄) were prepared through a literature method opportunely modified by us to make easier preparation and increase yield, which was higher than 70 % in all cases. The obtained products were the expected ones, as supported by the results of elemental analysis and ¹H NMR spectra. Their resistance to the thermal degradation in both flowing nitrogen and static air atmosphere was checked by degrading samples at 10 °C min^?1 and determining temperatures at 5 % mass loss (T _5%) and residues at 700 °C. The T _5% values in air were lower than the corresponding ones in nitrogen, but the trend among the various POSSs investigated was the same in both used atmospheres, with the most high value for the compound having the Ar–O–Ar aromatic bridge. The residues at 700 °C in air of the compounds having not hetero-atoms (O or S) in the aromatic bridge were higher than those in nitrogen, whilst no substantial difference was observed for the other ones.     

Molecular complex formation between l-phenylalanine and 18-crown-6 in H2O–DMSO solvents studied by titration calorimetry at T = 298.15 K

The standard thermodynamic parameters (Δ_r G°, Δ_r H°, TΔ_r S°) of the reaction of molecular complex formation between 18-crown-6 ether (18C6) and l-phenylalanine (Phe), [Phe18C6], have been obtained from calorimetric titration experiments carried out by means of the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–dimethylsulfoxide (H₂O–DMSO) solvents. Results show that the increase of the DMSO concentration in the mixed solvents brings about an increase of the [Phe18C6] complex stability and of the exothermicity of the reaction of complex formation.     

Facile Synthesis of Processable Semi-aromatic Polyamide Containing Thioether Units

A series of processable semi-aromatic polyamides containing thioether units have been developed. They were synthesized through the reaction of 4,4’-bis(4-chloroformylphenylthio)benzene (BPB-DC) and aliphatic diamine by the method of interfacial polycondensation. These polyamides had excellent thermal properties with glass transition temperatures (T_g) of 124–137.9°C, melting temperatures (T_m) of 306.4–324.1°C and initial degradation temperatures (T_d) of 409.5–437°C. They had wider processing windows than traditional semi-aromatic polyamides and can be processed by the melting method. They had better tensile strengths of 61.2–73.7 MPa, low-temperature mechanical properties, low water absorption of 0.17%–0.23%, low dielectric constants of 3.47–3.66 at 100 kHz and better melt flowability properties of 37.3 to 164.4 Pa. s, 48.2 to 281.7 Pa. s and 58.3 to 486.7 Pa. s at different shear rates, respectively. Additionally, these polyamides showed good corrosion resistance, they did not dissolve in solvents such as NMP, DMSO, hydrochloric acid (6 mol/L), H₃PO₄ and solution of NaOH (1 mol/L) etc.     

Heat of immersion of iron(III) oxides in water at 25°C

The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe₂O₃ (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, T_p, from 300 to 700°C. The samples were evacuated at outgassing temperature, T_o, between room temperature and 500°C at a pressure of 1 × 10^?2?2.7 × 10^?2N m^?2 for 6 h. The heat of immersion, h_i(J m^?2), of samples C and M increased with an increase in T_o and showed the maximum h_i at T_o =400°C, while sample F did not show the maximum up to T_o =500°C. The systematic correlation was not observed between h_i and T_p of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 10⁴ J mole^?1 H₂O.     

Recativity of solid silicon with hydrogen under conditions of a low pressure plasma

The reactivity of solid silicon with a dydrogen has been studied in a temperature range between about 10°C and ≈540°C at discharge currents up to ≈420 mA and a pressure of ≈0.13 mbar (0.1 torr). At a given current the reaction rate displays a pronounced maximum at a temperature T₁ ? 60°C and it approaches zero at T₂ ? 300°C; both T₁ and T₂ d pending on the discharge current. Consequently, chemical transport of silicon is possible in temperature as well as plasma gradients.     

Green and rapid preparation of thermally stable and highly organosoluble polyamides containing L‐phenylalanine‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximido moieties

A chiral diacid monomer containing L ‐phenylalanine‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximido unit was successfully synthesized in four steps and used in the preparation of a series of novel optically active polyamides by direct polycondensation with diverse aromatic diamines using 1,3‐dipropylimidazolium bromide under microwave dielectric heating. Ionic liquids (ILs) efficiently absorb microwave energy and thus are employed as solvent. By controlling the concentration of 1,3‐dipropylimidazolium bromide, reaction time and power level, high yield and moderate inherent viscosity polymers could be achieved in a very short period of time. All the resulting polymers exhibited excellent solubility in various organic solvents. The polyamides were found to have inherent viscosities in the range of 0.54–0.85 dL g^?1. These polyamides had glass‐transition temperatures (T_g) above 180°C, and a 10% weight‐loss temperatures in excess of 340°C with char yield at 800°C in nitrogen higher than 40%. A comparative study on effects exerted by microwave technique with conventional method is also presented. Copyright © 2009 John Wiley & Sons, Ltd.