Polymers from 2,5-difluoroterephthalic acid II. Poly(arylene ether)s containing pendant benzoyl groups

Poly(arylene ether)s (9) containing pendant benzoyl groups were prepared by the aromatic substitution reaction of 2,5-difluoro-4-benzoylbenzophenone (7) with bisphenol (8) in the presence of potassium carbonate in N,N-dimethylacetamide. The polycondensation proceeded smoothly at 170°C and produced the desired poly(arylene ether)s with inherent viscosities up to 0.79 dl/g. The polymers were quite soluble in common organic solvents and can be processed into uniform films from solutions. The thermogravimetry of the polymers showed excellent thermal stability, 10% weight losses above 450°C in nitrogen atmosphere. The glass-transition temperatures of the polymers were 138–158°C.     

Synthesis and enzymatic degradation of regular network aliphatic polyesters

Regular network aliphatic polyesters were prepared from glycerol (Yg) and a series of various length aliphatic dicarboxylic acids (HOOC-(CH2)_n−2-COOOH, n = 4–10, 12 and 14). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and post-polymerized at 230°C for various times to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. The degree of reaction (D_R) estimated from the infrared absorbance of -OH and >CH₂ or >CH groups increased with increasing post-polymerization time and length of methylene chain. The heat distortion temperature also increased with increasing post-polymerization time and was 55, 28, 15, 6, 0, −1, −5, 4 and 32°C for Yg4, Yg5, Yg6, Yg7, Yg8, Yg9, Yg10, Yg12 and Yg14 post-polymerized for 4 h, respectively. Wide angle X-ray scattering patterns showed a distinct single diffraction peak, suggesting some ordered structure due to the establishment of a regular network. Density, water absorption and weight loss by alkali hydrolysis decreased with increasing methylene chain length. The enzymatic degradation was estimated by weight loss of the network films in a buffer solution of lipase at 37°C. The films of Yg4, Yg5, Yg6 and Yg7 showed no weight loss, but the weight loss increased greatly for Yg8, Yg9 and Yg10, and then decreased abruptly for Yg12 and Yg14. This suggests that the enzymatic degradation is affected by network structure, which allows the lipase to penetrate, and by the concentration of the enzymatically degradable ester linkage.     

Alkyloxy-substituted liquid-crystalline aromatic copolyesters

Summary The synthesis and characterization of main chain liquid crystalline polyesters arising from 2,5-bispentyloxy substituted terephthalic aicd (3) and aromotic diols are described. 3 was prepared from diethyl 2,5-dihydroxyterephthalate and 1-bromopentane. The polyesters were prepared from 4,4-dihydroxybiphenyl (5), hydroquinone (6), 2,5-dimethyl hydroquinone (8) and the substituted terephthaloyl dichloride (4) in 1,1,2,2-terachloroethane. Their structures were characterized by ¹H-NMR, GPC and elemental analyses; their thermal behavior was studied by DSC measurements, microscopy under polarized light, and thermogravimetric analyses. The melting points are in the range of 130–280°C. All of them except of those with a high amount of 2,5-dimethyl hydroquinone (8) form a nematic phase above their melting point.     

Arylidene polymers. XVIII. Synthesis and thermal behavior of organometallic arylidene polyesters containing ferrocene derivatives in the main chain

A new interesting category of organometallic polyesters based on diarylidenecycloalkanones containing ferrocene derivatives in the polymer main chain has been prepared by interfacial polycondensation of 1,1′-dichlorocarbonyl ferrocene or 1,1′-dichlorocarbonyl-4,4′-diiodoferrocene with 2,5-bis(p-hydroxybenzylidene)cyclopentanone, 2,5-divanillylidenecyclopentanone, 2,6-bis(p-hydroxybenzylidene)cyclohexanone, 2,6-divanillylidenecyclohexanone, and 2,7-bis(p-hydroxybenzylidene) cycloheptanone. The resulting polyesters were characterized by elemental analyses, infrared spectroscopy, solubility, and viscometry measurements. The thermal behavior of the synthesized polymers was evaluated by thermal gravimetric analysis and correlated with their structures. The crystallinity of all polymers were examined by x-ray diffraction analysis. Moreover, the electrical conductivity of a selected example of polymer was investigated above the temperature range (300–500 K) and showed that it followed an Arrhenius-type equation with activation energy 2.09 eV. © 1993 John Wiley & Sons, Inc.     

Fabrication and conductivity of a new compound Ca2Cr2O5

A new brownmillerite-related compound. Ca₂Cr₂O₅, has been prepared. It has been indexed according to an orthorhombic lattice a = 5·750 Å, b = 14·398 Å and c = 5·483 Å. A series of experiments was performed in order to find the appropriate firing temperature. The total conductivity was measured by a four-point method in the range of 690–911°C. Impedance spectroscopy was also employed in the temperature range 343–785°C. Conductivity measurements at different oxygen pressures at 500°C suggest that Ca₂Cr₂O₅ is a predominantly ionic conductor at P_o2 = 1–10⁻²atm.     

Synthesis and properties of aliphatic spirodilactam diphenol containing polyesters

A series of aromatic polyesters containing 1,6-diazaspiro[4,4]-nonane-2,7-dione were synthesized under phase-transfer conditions. The copolymers were obtained in essentially quantitative yield, theses were soluble in common organic solvents, and would readily form clear, colorless films from solution. The optimum conditions of polymerization, was obtained via polycondensation at room temperature and reaction time of 4 h in chloroform. All polymers were characterized by FTIR, GPC, viscosity, water contact angle, water absorption, TGA, DSC and TMA. The prepared polyesters showed excellent thermal stability, as measured by TGA (10 wt% loss), are only moderate due to the alicyclic component and range from 365 to 401 °C in air; however, glass transition temperatures are quite high (245-309 °C). The inherent viscosities of these solutions ranged from 0.77 to 1.40 dl g⁻¹, depending on the polyester structure. The structures of the polyesters were confirmed by FTIR spectroscopy.     

The effect of sintering temperature variations on the development of electrically active interfaces in zinc oxide based varistors

A series of zinc oxide based varistors containing 0.5 wt.% Bi₂O₃ and 0.5 wt.% Mn₂O₃ were prepared by a conventional mixed oxide route and sintered at temperatures between 950 and 1300°C. All samples showed the varistor effect, although as the sintering temperature was increased above 1000°C, the non-linear coefficient decreased from 22 to 3 at 1300°C. Local grain boundary property measurements were carried out using remote electron beam induced current (REBIC) configuration conductive mode scanning electron microscopy. The proportions of electrically active interfaces and those showing strong resistive contrast were found to increase with sintering temperature.     

Synthesis of new polyesters containing phosphorus heterocycles and halogen

Two series of polyesters containing phenoxaphosphine rings and several halogens were synthesized by low-temperature solution polycondensation in the presence of triethylamine. One series, containing halogens only in the bisphenol moiety, was obtained from 2,8-dichloroformyl-10-phenylphenoxaphosphine-10-oxide and chlorinated bisphenol. In the second series, halogens belonged both to bisphenol and diacid dichlorides. For the last series, 2,8-dichloroformyl-10-(4-bromophenyl)phenoxaphosphine-10-oxide was prepared as a new monomer. All resulting polyesters were characterized by elemental analysis, reduced viscosity, IR and ¹H NMR spectroscopy, and thermogravimetric analysis. These polymers began to lose weight at about 400°C in air being seen as self-extinguishing ones.     

Bio-based semi-aromatic polyesters for coating applications

Linear and branched bio-based semi-aromatic (co)polyesters were evaluated as resins for solvent-based and powder coatings. Dimethyl-2,5-furandicarboxylate (DMF), 2,3-butanediol and various multifunctional comonomers were used to synthesize amorphous hydroxyl-end-capped (co)polyesters. The resins were cross-linked using the ?-caprolactam blocked trimer of isophorone diisocyanate. Both the solvent-based and powder coatings proved to be hard but brittle, which was a result of the very stiff molecular structure of the formed network. This was corroborated by the T_g values obtained for the coatings, which exceeded 100 °C for both the solvent-based and powder coatings. The poly(ester urethane) coatings prepared from the branched copolyesters show a reasonable solvent resistance. However, swelling occurred during the solvent treatment, indicating an insufficient network formation. The solvent-based and powder coatings exhibit similar mechanical and physical performance, showing that in this study there was no significant influence of the preparation method. In view of the obtained results it can be concluded that DMF-based branched polyesters are interesting candidates for solvent-based and powder coating applications.     

A comparative study of supported MoO3 catalysts prepared by the new “slurry” impregnation method and by the conventional method: their activity in transesterification of dimethyl oxalate and phenol

A new preparation method for supported MoO₃ catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO₃/water is used instead of the solution ammonium heptamolybdate, AHM [(NH₄)₆Mo₇O₂₄]. The MoO₃/γ-alumina, MoO₃/active carbon, and MoO₃/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO₃ was sufficient to transport molybdenum species from solid MoO₃ to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO₃/γ-Al₂O₃ catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO₃/SiO₂ catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH₄)₆Mo₇O₂₄. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.     

Physicochemical surface and catalytic properties of CuO–ZnO/Al2O3 system

A series of CuO–ZnO/Al₂O₃ solids were prepared by wet impregnation using Al(OH)₃ solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O₂ at temperatures ranged between 125°C and 200°C.

The results showed that CuO interacts with Al₂O₃ to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl₂O₄ at 600°C while stimulates its production at 800°C. The treatment of CuO/Al₂O₃ solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol⁻¹ in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature.     

La–Si–O–N glasses: Part I. Extension of the glass forming region

The nitrogen-rich part of the glass forming region in the La–Si–O–N system has been the subject of a comprehensive study. Glasses were prepared by heating powder mixtures of La metal, Si₃N₄ and SiO₂ in a nitrogen atmosphere at 1650–1800 °C. By this new synthesis route, glasses containing up to 68 e/o of N and 62 e/o of La were prepared, showing that the glass forming region is significantly larger than previously reported. The glasses were characterized by elemental analysis, differential thermal analysis, X-ray powder diffraction, and scanning electron microscopy. They were found to be X-ray amorphous and homogenous, with the majority of them containing small amounts of crystalline La silicides and elemental Si. Glass transition temperatures (T_g) were found to vary between 900 and 1100 °C and crystallization to occur typically 120 °C above T_g. The forming of the glasses was investigated by characterizing samples taken out at various steps of the heating cycle. The results indicate that the glass formation is strongly dependent on reaction kinetics. A strong exothermal reaction occurs at temperatures 900–1100 °C, leading to the formation of assemblies of amorphous and crystalline (oxy)nitride phases that melt upon further heating at 1650–1800 °C.     

The effect of annealing on tensile properties of injection molded biopolyesters based on 2,5-furandicarboxylic acid

In this study, we investigate four polyesters based on 2,5-furandicarboxylic acid and different diols including 1,2-ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, and 1,6-hexylene glycol. Poly(ethylene 2,5-furanoate), poly(propylene 2,5-furanoate), poly(butylene 2,5-furanoate), and poly(hexylene 2,5-furanoate) (PHF) were characterized by thermogravimetric analysis, X-ray diffraction, differential scanning calorimeter, and tensile tests. In addition, the influence of annealing polyesters on their thermal and mechanical properties was investigated. For these reasons samples for the tensile test were prepared by injection molding. The tensile properties of injection molded samples were compared with samples that were additionally annealed after injection molding. All studied polyesters after heating treatment showed multiple melting behavior. The increase in the degree of crystallinity significantly influenced also the mechanical properties of the samples. It was found that the length of the aliphatic chain and degree of crystallinity plays a major role in the final properties of furan-based polyesters.     

Design of photocrosslinkable polyesters with specific absorptions

2,5-Bis(4-hydroxy-3-methoxybenzylidene)cyclopentanone (DVCP), when condensed to form polyesters, polysulfonates, polycarbonates, and polyphosphonates, provides photocrosslinkable polymers useful in photoresist and photolithographic applications. With the use of 26 distyryl ketones related to DVCP, a series of polyesters have been prepared which reflect in their photoresponse the structural variations of the monomeric bisphenols. Those prepared from cyclopentanone are more light sensitive than those from acetone, cyclohexanone, etc. Methoxyl groups on the bisphenol enhance sensitivity and solubility and cause a bathochromic shift. Nitro- and ortho-hydroxyl substituents cause desensitization. Halogens on the bisphenol do not significantly change the polymer sensitivity or absorption. The polymers prepared from DVCP-type bisphenols usually show a hypsochromic shift of 30–40 nm from the monomer's absorption maximum. By selecting the proper bisphenol, one can “tailor” the absorption, sensitivity, and solubility of the resulting polyester. Most of the polyesters of this work were prepared from azelaoyl chloride or sebacyl chloride and had up to 50 mole-% of a nonlight-sensitive bisphenol such as tetrachlorobisphenol A present to improve their solubility in dichloroethane.     

Synthesis of TiO2 particles by reverse microemulsion method using nonionic surfactants with different hydrophilic and hydrophobic group and their photocatalytic activity

TiO₂ nanoparticles were prepared using hydrolysis of titanium tetraisopropoxide in W/O microemulsions consisting of water, nonionic Brij series surfactants with different hydrophilic and Tween series surfactants with different hydrophobic group, and cyclohexane. The properties of these particles were characterized by TEM, XRD, FT-IR, TGA and DTA. The photocatalytic degradation of p-nitrophenol has been studied in order to compare the photocatalytic activity of prepared nanosized titania. TiO₂ particles calcined at 500 °C have a stable anatase phase which has no organic surfactants and the product completely transforms into the anatase phase above 300 °C and the rutile phase begins to appear at 600 °C regardless of surfactants. The particles are shown to have a spherical shape and have an uniform size distribution but the shape becomes distorted with a decrease of hydrophilic group chain length according to rapid hydrolysis of water and titanium alkoxide. In addition, the crystallite size and crystallinity increase with a decrease of hydrophilic and hydrophobic group chain length and an increase of calcination temperature. The photocatalytic activity increases with an increase of hydrophilic and hydrophobic group length and the titania calcined at 500 °C shows the highest activity on the photocatalytic degradation of p-nitrophenol regardless of surfactants.     

Bacterial production of poly-3-hydroxyalkanoates containing arylalkyl substituent groups

6-Phenylhexanoic acid (6PHxA), 7-phenylheptanoic acid (7PHpA), 9-phenylnonanoic acid (9PNA), 11-phenylundecanoic acid (11PUA), 9-p-tolylnonanoic acid (9TNA) and 9-p-styrylnonanoic acid (9SNA) were prepared and evaluated as substrates for cell growth and polyester production by Pseudomonas oleovorans and Pseudomonas putida. P. putida was more effective than P. oleovorans for producing polyesters from these aromatic substrates. Poly-3-hydroxyalkanoates, PHAs, were obtained from 6PHxA, 7PHpA, 9PNA and 11PUA. The PHAs produced from all of these substrates contained mostly 3-hydroxy-5-phenylvalerate (H5PV) and 3-hydroxy-6-phenylhexanoate (H6PHx) units. Polymer yields ranging from 3 to 47% of cell dry weight were obtained with molecular weights ranging from 156 000 to 37 000 and polydispersities from 2.3 to 2.9. Cofeeding of most of these substrates with nonanoic acid produced mixtures of two different PHAs with different glass transitions, one in the region of −8 to 12°C for the PHA with arylalkyl substituent groups, and one in the region of −14 to −35°C for the PHA from nonanoic acid. The PHA from 9TNA also had a crystalline melting transition.     

Spontaneous hydrolytic degradability of copolyesters having tetrahydropyran rings in their backbones

Homo- and copolyesters, containing 2,5-linked tetrahydropyran rings in their backbones, were prepared by cationic ring-opening polymerization of bicyclic lactones, 2,6-dioxabicyclo [2.2.2] octan-3-one ( 1 ), and its 4-methoxy-carbonyl and 4-methoxy-carbonyl and 4-benzyloxycarbonyl derivatives ( 3 and 4 ). Copolyesters, having pendant carboxyl groups, were derived from the copolymers containing 4 as one of the comonomers by the catalytic hydrogenolysis of the pendant benzyloxy–carbonyl groups. Copolyesters, containing both 2,5-linked and 2,6-linked tetrahydropyran rings in the main chains, were obtained by the copolymerization of 1 with 6,8-dioxabicyclo [3.2.1] octan-7-one ( 13 ), which is a structural isomer of 1 . Spontaneous hydrolytic degradability of these polyesters was investigated in a phosphate buffer solution (pH 7.5) at 27°C. The degradability of the polyesters markedly depended on the molecular structure: hydrophobic pendant groups retarded the hydrolytic degradation, whereas hydrophilic pendant groups accelerated it. In particular, a small amount of pendant carboxyl groups significantly enhanced the hydrolytic degradability of the copolyesters from 1 . Polyesters, containing 2,6-linked tetrahydropyran rings in their backbones, underwent hydrolytic degradation more readily than those entirely consisting of 2,5-linked tetrahydropyran rings. © 1994 John Wiley & Sons, Inc.     

Aromatic polyesters containing different content of Thioether and methyl units: facile synthesis and properties

A series of aromatic polyesters containing thioether units were successfully synthesized in this paper. Two kinds of aromatic dichloride, (4,4’-thiodibenzoyl chloride (T-DC) and 4,4’-bis(4-chloroformylphenylthio)benzene (BPB-DC) with different sulfur content were prepared and reacted with bisphenol through interfacial reaction. These four kinds of aromatic polyesters were found to have excellent thermal and mechanical properties. Their glass transition temperatures (T_g) were in the range of 161.2–216.9 °C, the initial degradation temperatures (T_d) was up to 400–454 °C and tensile strengths of 68.9–114.9 MPa. Additionally, these aromatic polyesters present good optical transmittance within the range of 81.19–84.54% at 450 nm. More importantly, all polyesters exhibited outstanding flame retardant properties. The limiting oxygen indexes (LOIs) were ranged from 30 to 39 and UL-94 V-0 rating can be reached via this approach. In summary, the comprehensive performance of the four designed polyesters surpassed the traditional aromatic ones such as U-100.     

Investigations on the structure of fully hydrated portland cement and tricalcium silicate pastes. II. Total porosity and pore size distribution

On a series of OPC pastes hydrated at 20 °C and 90 °C and Ca₃SiO₅ pastes hydrated at 20 °C the total porosity and pore size distribution were measured. Data obtained by mercury porosimetry and nitrogen adsorption did not agree well as the volumina of pores filled with Hg and N₂ differed. Regardless on the method employed the found pore size distribution depended on the starting water-solid ratio; as equal porosity, it was different in different hydrated materials.     

Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300-400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.