Acetone transport in poly(ethylene terephthalate) and related phenomena

The acetone transport in poly(ethylene terephthalate) (PET) and related phenomena was investigated. Based on Harmon's model for Case I, Case II, and the anomalous transport, we analyzed the data of mass uptake. The diffusivity for Case I and the velocity for Case II satisfied the Arrhenius plot. It was found that the solvent moves from outer surfaces to the center according to Case I kinetics, and there is movement in the opposite direction according to Case II kinetics during the mass uptake. This result indicated that pure Case II behavior did not appear in the PET–acetone system. The saturated amount of acetone in PET satisfied the van't Hoff plot. X-ray diffraction pattern and DSC curve showed solvent-induced crystallites and thermal crystallites. The results of density measurement explained the difference of the sorption kinetics between the acetone-treated PET crystallites and thermally treated PET. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 163–169, 1998     

Studies of miscibility,transesterification and crystallization in blends of poly(ethylene terephthalate) and Poly(ethylene-2,6-naphthalene dicarboxylate)

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) were obtained by coprecipitation from solution followed by melt-pressing for different timest _mand quenching in iced water. When the melt-pressing time was 0.2 and 0.5 min, two glass transition temperaturesT _gwere observed by means of dynamic mechanical analysis (DMA), indicating that there are two phases present, a PEN-rich phase and a PET-rich phase. The differential scanning calorimetry (DSC) curves show two crystallization peaks and two melting peaks which, according to wide-angle x-ray scattering (WAXS) measurements, can be attributed to PET and PEN, respectively. In the case oft _m=2 min or longer, a single value ofT _gand thus a single phase is found to exist. Fort _m=10 min and 45 min no crystallization and melting at all is observed during heating with 10°C/min, indicating that a copolyester of PET and PEN has been formed by transesterfication during melt-pressing.Time-resolved WAXS measurements during isothermal crystallization show that, in the blend, the half-time of crystallization of PET is different from that of PEN, and not the same as that which is found in the pure polymer.Dedicated with best wishes to Prof. Dr. E.W. Fischer on the occasion of his 65th birthday     

Crystal and molecular structure of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole

An X-ray structural study of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole (1), one of the representatives of azoles with strong electron-withdrawing substituents, has been carried out. It has been found that in the orthorhombic modification of1 the conformations of the fluorodinitromethyl groups are different. Intermolecular contacts in the crystal are realized through the heterocycles arranged at large angles to each other. The presence of strong electron-withdrawing substituents results in shortening of the C-O bonds and in a certain increase in the OCN angle in the 1,3,4-oxadiazole ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 639–641, April, 1994.     

Water sorption/desorption kinetics in poly(ethylene naphthalene-2,6-dicarboxylate) and poly(ethylene terephthalate)

Water sorption/desorption experiments were carried out on films (～ 220 μm thick) of amorphous poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) stored in ambient conditions for different periods of time (0.5-4 years) and of poly(ethylene terephthalate) (PET) with different degrees of crystalinity levels (0-29%) by means of FTIR spectroscopy. Water sorption/desorption kinetics follows Fick's law for all samples investigated. Water sorption isotherms, obtained from gravimetric methods, indicate a larger sorption capacity in the case of PEN materials. The apparent diffusion coefficients (D) are larger in the case of PET samples. The observed D values decrease with storage time (physical aging) of PEN samples and with the crystallinity of PET samples. © 1995 John Wiley & Sons, Inc.     

Gas permeability,diffusivity, and solubility of poly(4-vinylpyridine) film

Although poly(4-vinylpyridine) is believed to have good gas permselectivity, the intrinsic gas permeation property is rarely reported in the literature. The objective of this work is to study the the intrinsic gas permeation property of poly(4-vinylpyridine) using a free-standing film. Because of its brittleness and strong adhesion with most solid surfaces, a free-standing poly(4-vinylpyridine) film was therefore prepared from casting on a liquid mercury surface. The permeation behavior of He, H₂, O₂, N₂, CH₄, and CO₂ through the film was tested over a pressure range of 252 to 800 cm Hg at 35°C. The permeability and solubility decrease slightly with an increase in pressure, whereas the diffusivity increases as pressure increases. The pressure-dependent phenomenon can be explained using the partial immobilization model and the dual sorption model. An effective gas molecule diameter, which is defined as the square root of the product of gas collision and kinetic diameters, was used to correlate the diffusivity and gas molecule size, and an empirical equation was derived. Solubility is also a strong function of gas physical properties such as critical temperature and Lennard–Jones force constant, which are the measures of gas condensability and molecule interaction, respectively. In general, higher solubility in a polymer is obtained for gases with greater condensability and stronger interaction. Typical gas permeabilities of poly(4-vinylpyridine) measured at 619 cm Hg and 35°C are: 12.36 (He), 12.64 (H₂), 3.31 (CO₂), 0.84 (O₂), 0.14 (CH₄), and 0.13 (N₂) barrers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2851–2861, 1999     

Synthesis,physical characterization,and acetone sorption kinetics in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) were synthesized by melt condensation. In a series of thin, solvent cast films of varying PEN content, acetone diffusivity and solubility were determined at 35°C and an acetone pressure of 5.4 cm Hg. The kinetics of acetone sorption in the copolymer films are well described by a Fickian model. Both solubility and diffusivity decrease with increasing PEN content. The acetone diffusion coefficient decreases 93% from PET to PET/85PEN, a copolymer in which 85 weight percent of the dimethyl terephthalate in PET has been replace by dimethyl naphthalate 2,6-dicarboxylate. The acetone solubility coefficient in the amorphous regions of the polymer decreases by approximately a factor of two over the same composition range. The glass/rubber transition temperatures of these materials rise monotonically with increasing PEN content. Copolymers containing 20 to 80 wt % PEN are amorphous. Samples with <20% or >80% PEN contain measurable levels of crystallinity. Estimated fractional free volume in the amorphous regions of these samples is lower in the copolymers than in either of the homopolymers. Relative free volume as probed by positron annihilation lifetime spectroscopy (PALS) decreases systematically with increasing PEN content. Acetone diffusion coefficients correlate well with PALS results. Infrared spectroscopy suggests an increase in the fraction of ethylene glycol units in the trans conformation in the amorphous phase as the concentration of PEN in the copolymer increases. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2981–3000, 1998     

Structures of substituted di-aryl-1,3,4-oxadiazole derivatives: 2,5-bis(pyridyl)- and 2,5-bis(aminophenyl)-substitution

Crystal structures of four different di-aryl-1,3,4-oxadiazole compounds (aryl = 2-pyridyl-, 3-pyridyl-, 2-aminophenyl-, 3-aminophenyl-) are determined. Crystallization of di(2-pyridyl)-1,3,4-oxadiazole yielded monoclinic and triclinic polymorphs. The structures are characterized by the occurrence of π–π interactions. Additionally, in case of the aminophenyl compounds intra- as well as intermolecular hydrogen bonds are found that influence the packing motif as well. Since these molecules are often used as ligands in metal–organic complexes similarities and differences of the molecular conformation between the molecules in the pure crystals and that of the ligands in the complexes are discussed.     

Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2973–2984, 1999     

Ethylbenzene solubility,diffusivity, and permeability in poly(dimethylsiloxane)

The pure‐gas sorption, diffusion, and permeation properties of ethylbenzene in poly(dimethylsiloxane) (PDMS) are reported at 35, 45, and 55 °C and at pressures ranging from 0 to 4.4 cmHg. Additionally, mixed‐gas ethylbenzene/N₂ permeability properties at 35 °C, a total feed pressure of 10 atm, and a permeate pressure of 1 atm are reported. Ethylbenzene solubility increases with increasing penetrant relative pressure and can be described by the Flory–Rehner model with an interaction parameter of 0.24 ± 0.02. At a fixed relative pressure, ethylbenzene solubility decreases with increasing temperature, and the enthalpy of sorption is −41.4 ± 0.3 kJ/mol, which is independent of ethylbenzene concentration and essentially equal to the enthalpy of condensation of pure ethylbenzene. Ethylbenzene diffusion coefficients decrease with increasing concentration at 35 °C. The activation energy of ethylbenzene diffusion in PDMS at infinite dilution is 49 ± 6 kJ/mol. The ethylbenzene activation energies of permeation decrease from near 0 to −34 ± 7 kJ/mol as concentration increases, whereas the activation energy of permeation for pure N₂ is 8 ± 2 kJ/mol. At 35 °C, ethylbenzene and N₂ permeability coefficients determined from pure‐gas permeation experiments are similar to those obtained from mixed‐gas permeation experiments, and ethylbenzene/N₂ selectivity values as high as 800 were observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1461–1473, 2000     

1,2,3-Selenadiazolyl-1,3,4-oxadiazole, 1,2,3-Thiadiazolyl-1,3,4-oxadiazole and 5-(1,2,3-Thiadiazolyl)-s-triazolo[3,4-b]-1,3,4-thiadiazoles

A series of 5-substituted-2-(4-alkyl or phenyl-1,2,3-thia(or selena)diazol-5-yl)-1,3,4-oxadiazoles were prepared. 5-Substituted-2-(4-phenyl-1,2,3-selenadiazol-5-yl)-1,3,4-oxadiazoles upon pyrolysis afforded the corresponding alkynes. Also, a series of 5-substituted-4-amino-3-(1,2,3-thiadiazol-5-yl)-s-triazoles and 5-(1,2,3-thiadiazolyl)-s-triazolo[3,4-b]-1,3,4-thiadiazoles were prepared.     

Synthesis and characterization of poly(1-benzoylsemicarbazide) and poly(1,3,4-oxadiazole amine) from 2-(p-aminophenyl)-1,3,4-oxadizolin-5-one via ring-opening

A novel thermally stable and semiconducting polyheterocycle, poly(1,3,4-oxadiazole amine), was synthesized from 2-(p-aminophenyl)-1,3,4-oxadiazolin-5-one via ring-opening. The polymer is a new class of ordered alternating copoly(aniline) containing 1,3,4-oxadiazole heterocyclic units. The polymer is highly thermally stable and exhibits no weight loss up to 370°C in air. Its electric conductivity is less than 10⁻¹⁰ S · cm⁻¹ at ambient temperature, but markedly increases to 6,5 · 10⁻⁷ S · cm⁻¹ upon doping with iodine.     

Reaction of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole with primary amines. Synthesis of 4-substituted-3,5-bis(trifluoromethyl)-4H-1,2,4-triazoles

Reaction of 3,5-bis(trifluoromethyl)-1,3,4-oxadiazole ( 1a ) with primary amines under a variety of conditions conveniently produced 4-substituted-3,5-bis(trifluoromethyl)-4H-1.2,4-triazoles 4a in 26-85% yield. Alkyl amines reacted with 1a in methanol at ?42° to provide hydrogen-bonded monoadduct-methanol complexes 5a , as determined by X-ray. The reaction of 1a with sterically hindered or strongly electron deficient anilines required high temperatures in the absence of solvent.     

Thermal,crystallization, mechanical,and rheological characteristics of poly(trimethylene terephthalate)/poly(ethylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) in the amorphous state were miscible in all of the blend compositions studied, as evidenced by a single, composition‐dependent glass‐transition temperature observed for each blend composition. The variation in the glass‐transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.91. The cold‐crystallization (peak) temperature decreased with an increasing PTT content, whereas the melt‐crystallization (peak) temperature decreased with an increasing amount of the minor component. The subsequent melting behavior after both cold and melt crystallizations exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of the minor component of the blends. During crystallization, the pure components crystallized simultaneously just to form their own crystals. The blend having 50 wt % of PTT showed the lowest apparent degree of crystallinity and the lowest tensile‐strength values. The steady shear viscosity values for the pure components and the blends decreased slightly with an increasing shear rate (within the shear rate range of 0.25–25 s^?1); those of the blends were lower than those of the pure components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 676–686, 2004     

A new series of 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole derivatives: their synthesis and fluorescence properties for anion sensors

A new series of 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole derivatives containing various substituted groups on the ortho-position to oxadiazole ring was synthesized and their fluorescent sensor properties were investigated. The fluorescent sensor molecules showed UV absorption shift as well as fluorescence emission shift upon exposure to fluoride anion in DMF solution, which was considerably dependent on the substituent attached on the phenyl group. The new sensory compound, 1d can be used as a fluoride anion sensor in terms of naked-eye detection and fluorescent sensing with high selectivity.     

Spectral and luminescent properties of 2-(2-hydroxyphenyl)-5-(2,6-difluorophenyl)-1,3,4-oxadiazole and its methoxy and benzyloxy derivatives

Russian Journal of General Chemistry -     

Birefringence,compliance, and viscoelasticity of poly(ethylene terephthalate) fibers

The experimental relation between birefringence and dynamic compliance has been determined for a wide range of poly(ethylene terephthalate) fibers. This relation is explained by two complementary versions of the series aggregate model. The classical series aggregate model provides a satisfactory interpretation of the data for the low-oriented fibers. A model developed earlier for aramid fibers explains the data for the well-oriented fibers. By monitoring the dynamic compliance during creep and stress relaxation of well-oriented fibers it is shown that these phenomena are caused by shear relaxation, resulting in a progressive contraction of the chain orientation distribution.     

Synthesis of benzoates of 1,4-bis(2,5-dimethyl-4-hydroxypiperidino)-2-butene and 1,4-bis-(2,5-dimethyl-4-hydroxypiperidino)-2-butyne

1,4-Bis(2,5-dimethyl-4-hydroxypiperidino)-2-butene and 1,4-bis(2,5-dimethyl-4-hydroxypiperidino)-2-butyne (II and III) were obtained by the action of 1,4-dibromo-2-butene and 1,4-dibromo-2-butyne on the form of 2,5-dimethyl-4-piperidol (I). The benzoates (IV and V) were obtained by acylation of II and III with benzoyl chloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 352–353, March, 1971.     

2,5-二[2′-(4′-氯代苯氧乙酸)基]-1,3,4-噻二唑的合成

通过对称双酰肼与P_2S_5的缩合反应合成2,5-二-羟苯基-1,3,4-噻二唑,并由此制备了2,5-二[2′-(4′-氯代苯氧乙酸)基]-1,3,4-噻二唑及其相关化合物,同时测定了它们的生物活性。