Thermal behaviour of poly(2,6-dimethoxy-1,4-phenylene ether)

Thermodynamic properties of semicrystalline and completely amorphous samples of poly(2,6-dimethoxy-1,4-phenylene ether) have been studied by DSC-calorimetry. A very low entropy of fusion indicates that only minor conformational changes take place during the melting. The low value of the configurational entropy of the glass transition is due to the faci that the theoretical second order transition is closely related to the glass transition point.     

Preparation of poly(1,4-phenylene)s by electro-oxidative polymerization

The effect of substituents on the electropolymerization of benzene derivatives and the redox properrties of the corresponding polymers were determined using Brown's substituent constants (σ⁺). Electron-donating groups lower the oxidation potential by which increase in the current efficiency was observed. However, stabilization of the produced cation radicals by the electron-donating groups resulted in a decrease in the polymerization efficiency. The appropriate values of σ⁺ for the efficient polymerization ranged near ?1.5.     

Flammability and thermal behaviour of phosphorus-containing polyamides. Copolymers of poly(1,4-phenylene terephthalamide), poly(1,3-phenylene isophthalamide), poly(1,4-phenylene sebacylamide) and poly(1,3-phenylene sebacylamide)

Some flame retardant copolyamides derived from 1,4-phenylenediamine or 1,3-phenylenediamine and N,N′-bis[(dialkoxyphosphinyl)methyl]1,4-benzenediamine with terephthaloyl or isophthaloyl, or sebacoyl dichlorides, are reported. Thermal and thermo-oxidative stability were studied by means of TGA. The influence of chemical structure in enhancing thermo-oxidative resistance of copolyamides was established. In the case of sebacylamides the DSC thermograms were also obtained. The flammabilities of the copolymers were determined by means of the limiting oxygen index; in the case of sebacylamides, the limiting nitrous oxide index was also determined. Comparison of LN₂OI with the LOI in sebacylamides reveals that the action of the flame retardant groups affects mainly the condensed phase decomposition. This view is also supported from the new stage of decomposition revealed in the DTGA thermograms.     

Synthesis and characterization of poly[2,5-bis(triethoxy)-1,4-phenylene vinylene]

The synthesis of a highly soluble, 2,5-disubstituted poly(p-phenylene vinylene) with pendant side chains containing ether groups was accomplished by a dehydrochlorination route. Specific interactions of the oxygen-containing side chains with the solvent are presumably responsible for the high solubility of the polymer, especially in protogenic solvents. The polymer microstructure was characterized by ¹H- and ¹³C-NMR. The polymer showed solvatochromic properties when dissolved in a variety of solvents. The relatively high molecular weight (M_n = 17,000) permitted the fabrication of free-standing films. The electrical conductivity of iodine-doped films was approximately 2 × 10^–2 S cm^–1. © 1995 John Wiley & Sons, Inc.     

2,5-二辛氧基聚对苯的合成及表征

蓝色电致发光;2;5-二辛氧基聚对苯的合成及表征     

Unperturbed dimensions of poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly(2,6-diphenyl-1,4-phenylene oxide) chains

The unperturbed chain dimensions of unfractionated poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly-(2,6-diphenyl-1,4-phenylene oxide) have been measured by combining molecular weight data from light scattering with intrinsic viscosity data in chloroform. The unperturbed chain dimensions of the former polymer were also measured directly by light scattering dissymmetry in a critical consolute solvent mixture (methyl cyclohexane: 1,4-dioxane 50:50 by volume). The results of these measurements and of measurements reported by other investigators are satisfactorily explained by postulating no dimension-expanding prejudice in azimuthal angle in chain conformers of the 2,6-substituted-1,4-phenylene oxide polymers. This corresponds to equal population of the two chain rotation energy minima at azimuthal angles 90° and 270°. Accepting this postulate, one calculates from the observed chain dimensions that the C? O? C bond angle is 118–120° in these aromatic polyethers in solution.     

Transitions and relaxations in poly(1,4-phenylene ether)

Transitions and relaxation phenomena in poly(1,4-phenylene ether) were studied over temperature range from 100 to 800°K by applying a combination of calorimetric, dilatometric, dynamic mechanical, and dielectric techniques. Amorphous polymer, exhibiting no x-ray crystallinity, is obtained only by quenching molten samples at extremely fast cooling rates (ca. 1000°C/sec) and by minimizing thermal gradients within specimens. A weakly active mechanical relaxation region with a loss maximum at 155°K of unknown origin was observed. The glass transition interval of completely amorphous polymer is characterized by a discontinuous jump in heat capacity of 2.76 cal/deg per chain segment occurring at 363°K (corrected for kinetic effects), and a fourfold increase in the coefficient of linear thermal expansion. Strongly active, dynamic mechanical relaxations occur in the T_g interval with a loss maximum at 371°K (f = 110 cps) and resulting in a drop in the dynamic storage modulus from 10¹¹ to 10⁹ dyne/cm². Cold crystallization takes place just above T_g, to yield a polymer with an x-ray crystallinity of 0.7 and a heat of crystallization of 270 cal/mole. The crystalline polymer shows a complex melt structure. Depending upon the thermal history, multiple endothermic peaks indicative of structural reorganizations occur just prior to fusion. Very high dielectric losses with a wide distribution of relaxation times were observed in the melt interval. The mechanical relaxation spectrum in this region is typical of viscous flow behavior.     

Model reactions for preparing poly(imino-tetrafluoro-1,4-phenylene)

2,3,4,5,6-Pentafluoroformanilide was prepared giving, in addition, two new compounds 4,5,6,7-tetrafluoro-1-pentafluorophenyl-benzimidazole and 2,3,4,5-tetrafluoro-6-[(pentafluorophenyl)amino]formanilide. Sodium 2,3,4,5,6-pentafluoro-formanilide was reacted with hexafluorobenzene in a molar ratio of 1:4 to give oligomers of α-pentafluorophenyl-ω-fluoro-poly(imino-tetrafluoro-1,4-phenylene). Some of the oligomers were isolated. The results indicate that poly(imino-tetrafluoro-1,4-phenylene) could be formed. Model reaction on hexafluorobenzene with sodium acetanilide, molar ratio 1:2, gave a low yield of N,N′-diacetyl-diphenyl-tetrafluoro-1,4-phenylenediamine.     

Direct metalation of poly(2,6-dimethyl-1,4-phenylene ether)

Poly(2,6-dimethyl-1,4-phenylene ether) (I) was metalated with butyllithium in tetrahydrofuran and with the N,N,N′,N′-tetramethylethylenediamine complex of butyllithium in a variety of solvents. In these cases, metalation occurred at both the ring and side chain positions, the former being preferred initially. Subsequently, there was an isomerization in favor of the side chain. At 25°C, there is no significant amount of polymer scission or crosslinking during metalation, but some crosslinking occurs on derivatizing with dimethyl sulfate and trimethylchlorosilane for high extents of ring metalation. With sodium and potassium alkyls, only side-chain metalation was observed. The metalated polymer reacts as a typical organometallic, allowing polymer modification by a wide variety of reactions.     

Single crystals of poly(2,6-dimethyl-1,4-phenylene)oxide

Summary Poly(2,6-dimethyl-1,4-phenylene)oxide crystals obtained from 0.1%-pinene solutions by isothermal growth at temperatures from 80–90 as well as 100 °C, were investigated by optical and X-ray diffraction techniques. A study has been made by differential scanning calorimetry in order to measure the melting point, glass transition and melting point depression temperatures of mixtures of the polymer with-chloro-naphthalene.The densities of the dry mats of single crystals were measured by a flotation method.

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Zusammenfassung Poly(2,6-dimethyl-1,4-phenylen)oxid Kristalle, die aus 0,1% igen-Pinen-Lösungen durch isothermes Wachstum bei Temperaturen von 80–90 sowie 100 °C erhalten wurden, wurden optisch und röntgenographisch untersucht. Mit der Differential-scanning-Kalorimetrie ergaben sich die Werte des Schmelzpunkts, der Glastemperatur und der Schmelzpunktdepressionen von Mischungen des Polymeren mit-Chlornaphthalin. Die Dichten der trockenen Matten aus Einkristallen wurde mit der Flotationsmethode gemessen.

     

Thermodynamic properties of poly(2,6-dimethyl-1,4-phenylene ether)

The thermodynamic properties of crystalline and amorphous poly(2,6-dimethyl-1,4-phenylene ether) (PPO

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polymer, General Electric Co.) have been studied calorimetrically between 80 and 570°K. The calculated configurational entropy of this polymer, of similar magnitude to other glass-forming liquids, is consistent with the combination of an unusually high ratio of T_g/T_m, and a low melting entropy.