High Thermo-oxidative Stability Research Articles

Fixing of Si−H groups on the surface of dispersed silica and their physical and chemical properties

Fixed Si−H bonds on silica surface by pyrolysis of polydimethylsilane were obtained. They have high thermooxidative stability and show selective sorption of some inorganic ions.

Investigation of the HF-catalyzed condensation reaction to diarylhexafluoropropanes

HF-catalyzed condensation of 2-hydroxy-2-arylhexafluoropropanes, e.g. I, with suitably substituted arenes, e.g. II, leads to hexafluoroisopropylidene-bridged intermediates, e.g. III, for 6F-monomers. ▪ The condensation reaction was carried out with several substrates, side products were characterized and their formation under different reaction conditions was studied. 6F-Monomers are building blocks for a variety of polycondensates with high thermo-oxidative stability and low dielectric constant.

New developments in thermally stable polymers

AbstractAdvances in high‐temperature polymers since 1985 are discussed with the emphasis on the chemistry. High‐temperature polymers refer to materials that exhibit glass‐transition temperatures > 200°C and have the chemical structure expected to provide high thermooxidative stability. Specific polymers or series of polymers were selected to show how the chemical structure influences certain properties. Poly(arylene ethers) and polyimides are the two principal families of polymers discussed. Recent work on poly(arylene ethers) has concentrated on incorporating heterocyclic units within the polymer backbone. Recent polyimide work has centered on the synthesis of new polymers from novel monomers, several containing the trifluoromethyl group strategically located on the molecule. Various members in each of these polymer families display a unique combination of properties, heretofore unattainable. Other families of polymers are also briefly discussed with a polymer from an AB maleimidobenzocyclobutene exhibiting an especially attractive combination of properties.

Synthesis and characterization of polybenzimidazoles carrying additional pyridine and imidazole groups in the main chain

Six polybenzimidazoles have been prepared by a dispersion polycondensation process using polyphosphoric acid as a dehydrating reagent. Two of these contained an additional pyridine residue in the mainchain, and three of them additional imidazole groups. The molecular structures have been characterized by u.v., i.r. and 1H n.m.r. spectra. Physical characterization has involved solubility measurements, solution viscosity evaluation and thermal stability assessment via thermogravimetric analysis. The latter has confirmed that the inherently high thermo-oxidative stability of polybenzimidazoles is retained in the case of polymers and copolymers with additional nitrogen heterocycles in the mainchain.

Polyimides containing carbonyl and ether connecting groups. II

AbstractIn a continuation of our effort on polyimides containing carbonyl and ether connecting groups between aromatic rings, several new polyimides were prepared and characterized. A few of these polymers were semi‐crystalline. Glass transition temperatures ranged from 164 to 258°C and crystalline melt temperatures were observed between 350 and 424°C. The semi‐crystalline polyimide from the reaction of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl)benzene provided transparent orange films with excellent tensile properties, exceptional resistance to solvents and strong base, and high thermooxidative stability. In addition, this polyimide provided excellent adhesive strength for joining titanium (6A1–4V) to titanium.

Investigation of thermooxidative stability of oils by thermal analysis methods

Two base oils, obtained on a laboratory scale, were investigated with a derivatograph and by means of DSC. The sensitivities of the oils to some antioxidants were also examined. The high thermooxidative stability of the oil obtained from a preoxidized atmospheric crude residue was confirmed.

Studies on heat‐resistant poly(metal phthalocyanine)‐imide copolymers

AbstractSeveral new poly(metal phthalocyanine)imide copolymers have been prepared using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BPTDA), metal(11) 4,4′,4″,4″′‐phthalocyanine tetraamines (MPTA), p‐phenylenediamine, 4,4′‐methylenedianiline, and 9,9‐bis(4‐aminophenyl)‐fluorene (BAF). The attractive feature of these polymers is their high thermooxidative and thermal stability. The polymer decomposition temperatures of all the imide copolymers are greater than 500°C in air and N atomspheres. Another noteworthy property is their high char yield: 60–78% at 800°C in a N2 atmosphere. Variation of the metal phthalocyanine concentration has a remarkable effect on the thermal stability and degree of polymerization. The most preferred molar proportion of the reagents MPTA, diamine, and BTDA is 1.25:7.5:10. These polymers may be useful in the preparation of heat‐resistant films and fibers.

Hydrolytically stable fluorocarbon ether bibenzoxazole polymers

AbstractHydrolytically and thermooxidatively stable fluorocarbon ether bibenzoxazole (FEB) polymers were synthesized by the acetic acid‐promoted polycondensation of fluorocarbon ether bis(o‐aminophenol) monomers with novel fluorocarbon ether dithioimidate ester monomers. The dithioimidate esters were derived from hexafluoropropylene oxide (HFPO) or, preferably, from a combination of HFPO and tetrafluoroethylene oxide (TFEO). The latter class of TFEO:HFPO‐derived dithioimidate esters imparted improved hydrolytic stability to the resultant FEB polymers while minimizing undesirable, concomitant increases in polymer glass transition temperatures. The polymers exhibited inherent viscosities in the range of 0.20 to 0.41 dl/g. Polymer structures were verified by elemental and infrared (IR) spectral analyses. Lower glass transition temperatures were obtained with increased fluorocarbon ether content, a minimum value of −48°C being achieved. High thermooxidative stability of the HFPO‐ and TFEO:HFPO‐based FEB polymers was substantiated by thermogravimetric analysis and isothermal aging studies in air. After isothermal aging in air for 200 hr at 288 and 260°C, representative polymers exhibited weight losses of 17 and 7%, respectively. Hydrolytic stability of the polymers was evaluated by exposure to a 95% relative humidity, 93°C environment for prolonged periods of time. Based on comparative glass transition temperature, inherent viscosity, and IR spectral data, the HFPO‐ and TFEO:HFPO‐based FEB polymers exhibited vastly improved hydrolytic stability over analogous TFEO‐based FEB polymers. Optimum hydrolytic stability and low‐temperature viscoelastic properties were achieved by the use of a TFEO:HFPO‐derived dithioimidate ester that did not contain structural isomers that would lead to sites of hydrolytic instability in the polymer backbone.

Experimental investigation of elastic turbulence and boundary slip of elastomers over a broad temperature interval

Ethylene-propylene copolymer, a typical stereo rubber, has been investigated by capillary viscometry. Ethylene-propylene copolymer possesses high thermooxidative stability, which has made it possible to study its viscosity properties, determine the onset of elastic turbulence and boundary slip, and measure the slip rate over a very broad temperature interval, from room temperature to 260° C. The flow of elastomers differs from that of thermoplastics in that at relatively low strain rates flow is complicated by the boundary slip effect. The mean boundary slip velocities of the copolymer at shear stresses above 106 dynes/cm2 are measured in tens of centimeters per second. As the temperature rises, they rapidly increase.

Cationic polymerization of 1-vinyl-2,2,3,3-tetrafluorocyclobutane oxide

1. The polymerization of 1-vinyl-2,2,3,3-tetrafluorocyclobutane oxide in the presence of cationic catalysts (BF3 etherates, FeCl3, Al2(SO4)3·3H2SO4·7H2O, SnCl4, or Al(C2H5)3+H2O) has been studied for the first time; high molecular weight polymers can be prepared when Al2(SO4)3·3H2SO4·7H2O, SnCl4, or Al(C2H5)3 +H2O is used. 2. The high molecular polymers of 1-vinyl-2, 2, 3,3-tetrafluorocyclobutane oxide prepared under the consitions indicated are amorphous and rubber-like materials with relatively high thermooxidative stability.