X-ray investigation of the structure of poly(tetramethylene terephthalate)

Poly(tetramethylene terephthalate) (PTMT) undergoes a reversible stress-induced crystal-crystal phase transition. X-ray fiber-diffraction photographs were obtained from the oriented, unstressed (α) phase. Relative intensities were measured from these photographs. These were used to help check the reported structures of the α phase. Structures and observed intensity data from other authors were also utilized. Results show the α phase contains a non-trans, non-gauche bond rotation in the tetramethylene chain and a nonplanar terephthalic acid residue. A tilt of 3.5° between the fiber axis and the c axis was determined in a direction 210° counterclockwise from the b^* axis.     

Infrared studies of the reversible stress-induced crystal-crystal phase transition of poly(tetramethylene terephthalate)

The reversible stress-induced crystal-crystal phase transition of poly(tetramethylene terephthalate) (PTMT) has been studied using infrared spectroscopy. Two spectral regions were used to study this transition: the 900–1000 cm^?1 methylene rocking region and the 1300–1550 cm^?1 methylene bending region. The bands at 917 and 1456 cm^?1 are assigned to the ∝ phase. The bands at 935 and 1388 cm^?1 have components from the α phase and the β phase. Dynamic stretching experiments performed above and below the glass-transition temperature indicated different mechanisms of the phase transition.     

Multiple endothermic melting behavior in poly(tetramethylene terephthalate)-containing polyesters and block copolyether-esters

The multiple endothermic behavior of poly(tetramethylene terephthalate) (PTMT) and its random and block copolymers with poly(tetramethylene isophthalate) (PTMI) and poly(tetramethylene oxide) (PTMO) is described. The differential scanning calorimetry heating scans of these polymers exhibit up to four endotherms. Endotherm I, the lowest-temperature endotherm, is an annealing peak and is ascribed to a clustering of PTMT sequences. Endotherms II, III, and IV are associated with crystal populations originated during periods of isothermal crystallization, cooling, and heating, respectively. The dependence of the endotherms on sample composition, crystallization and annealing temperatures, crystallization and annealing times, and sample cooling and heating rate is discussed.     

The structure of electron beam-modified poly(ethylene terephthalate) films

The effect of electron-beam irradiation on the surface properties and the parameters of the semicrystalline structure of biaxially oriented poly(ethylene terephthalate) (PET) films was studied. It was shown that the crystallinity and the surface tension of the irradiated films at the interfaces with isooctane and water vary in a nonmonotonic manner over the dose range D= 25–300 kGy. As the absorbed dose increases, the dispersion and polar terms of surface energy increase, exhibiting an extremum as a result of the competing chain crystallization and amorphous-phase formation processes, as well as oxidative degradation and crosslinking of PET samples.     

The mechanical properties and structure of poly(m-methylene terephthalate) fibers

A study has been carried out of the differences in mechanical properties of oriented fibers of poly(ethylene terephthalate) (2GT), poly(trimethylene terephthalate) (3GT), and poly(tetramethylene terephthalate) (4GT). The properties studied include the tensile stress–strain behavior, the recovery from strain, shrinkage at 100°C and the glass-transition temperatures. The stress–strain curves of the three materials differ markedly. 2GT shows a monotonic increase in stress with increasing strain up to failure, which occurs at ～20% strain, and the oriented fibers possess a comparatively high initial modulus. 3GT shows a much lower initial modulus and there is an inflection in the stress–strain curve at about 5% strain. The stress–strain curve of 4GT shows a number of distinct features. Although the initial modulus of 4GT is similar to that of 3GT, the stress–strain curve shows a pronounced plateau in the region between 4% and 12% strain. At higher strains the stresses rise rapidly before failure. These features of the stress–strain curves in the three polymers can be related to previous studies where the x-ray diffraction spectrum and the Raman spectrum have been examined for fibers under stress. The ranking of both the recovery and shrinkage behavior of these materials is in the order 3GT > 4GT > 2GT. These results can also be understood in terms of the results of the previous structural studies, and it is concluded that the molecular conformations in both the crystalline and noncrystalline regions play a key role in determining the mechanical behavior.     

The three-phase structure and mechanical properties of poly(ethylene terephthalate)

The relation between the mechanical properties and the microstructure of PET has been investigated, combining results from WAXS, SAXS, FTIR, DSC, and uniaxial compression tests. The rigid amorphous fraction in the PET was explicitly taken into consideration in interpreting structure–property relations. WAXS results prove that glass crystallized PET with a high volume fraction of rigid amorphous material and small crystal size, on uniaxial compression shows a considerable loss in crystalline fraction. FTIR results in combination with these WAXS results suggest that during this loss in crystallinity, short-range conformational order is retained, while long-range structural order is lost. At the same time, material with small crystals and a high amount of rigid amorphous material was found to show unexpectedly low yield stress. It is concluded that in the interpretation of these phenomena it is necessary to take the three-phase structure of PET, including the rigid amorphous fraction into account. This is expected to hold for other semicrystalline polymers, where a rigid amorphous fraction is prominent, such as PHB, PBT, PEN, PEEK, etc. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2092–2106, 2004     

Crystal structure and conformational disorder of poly(hexamethylene terephthalate)

Packing polymorphism and conformational disorder of poly(hexamethylene terephthalate) were analyzed by x-ray diffraction technique. The measurements were performed in the temperature range from 20 to 135°C. At high temperature, several unassignable reflections were found to disappear, and all reflections were satisfactorily indexed by single-chain unit cell. The crystal structures of β form (135°C) and β form (20°C) were similarly triclinic. The β′ unit cell assumed the double b-axis dimension, and the centrosymmetric conformations of the two chains adjacent along the b-axis differed in the orientation of the phenylene rings. At the elevated temperature (β form), the chains were indistinguishable by x-ray diffraction owing to the ring-flipping motion. The β and β′ structures were different in the local conformational disorder around the terephthaloyl groups. Conformational polymorphism of homologous poly(oligomethylene terephthalate)s was considered to originate from the difference in bulkiness of the aromatic and aliphatic residues. © 1996 John Wiley & Sons, Inc.     

Multicomponent solubility parameters of poly(vinyl chloride) and poly(tetramethylene glycol)

The one-, two-, and three-dimensional solubility parameter models were used to analyze solution thermodynamic data of several solutes in poly(vinyl chloride) (PVC) and poly(tetramethylene glycol) (polytetrahydrofuran, PTHF). A previous proposed method to estimate solubility parameter, based on direct minimization of the sum of the squares of errors in the prediction of χRT/V, was extended to two- and three-dimensional, and the results of solubility parameter components were the same as the linear regression method. The one-dimensional model gave the smallest sum of the squares of errors, followed by the three-dimensional model, then the two-dimensional model. A systematic error was identified when two- and three-dimensional models were used for the data. A method using less weight on polar and hydrogen-bonding components produced smaller errors for the two- and three-dimensional models.     

High‐pressure DTA of poly(butylene terephthalate), poly(hexamethylene terephthalate), and poly(ethylene terephthalate)

Pressure effect on the melting behavior of poly(butylene terephthalate) (PBT) and poly(hexamethylene terephthalate) (PHT) was studied by high‐pressure DTA (HP‐DTA) up to 320 and 530 MPa, respectively. Cooling rate dependence on the DSC melting curves of the samples cooled from the melt was shown at atmospheric pressure. Stable and metastable samples were prepared by cooling from the melt at low and normal cooling rates, respectively. DTA melting curves for the stable samples showed a single peak, and the peak profile did not change up to high pressure. Phase diagrams for PBT and PHT were newly determined. Fitting curves of melting temperature (T_m) versus pressure expressed by quadratic equation were obtained. Pressure coefficients of T_m at atmospheric pressure, dT_m/dp, of PBT and PHT were 37 and 33 K/100 MPa, respectively. HP‐DTA curves of the metastable PBT showed double melting peaks up to about 70 MPa. In contrast, PHT showed them over the whole pressure region. HP‐DTA of stable poly(ethylene terephthalate) (PET) was also carried out up to 200 MPa, and the phase diagram for PET was determined. dT_m/dp for PET was 49 K/100 MPa. dT_m/dp increased linearly with reciprocal number of ethylene unit. The decrease of dT_m/dp for poly(alkylene terephthalate) with increasing a segmental fraction of an alkyl group in a whole molecule is explained by the increase of entropy of fusion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 262–272, 2000     

Crystal structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate)

The structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate) (PTT) are revealed in detail by DSC, AFM, TEM, and WAXD as well as in situ FTIR and SAXS techniques. There is no effect of crystallization temperature and initial state on the crystal modification, yet the morphology is strongly affected by these two factors. First, the small rod-like lamellae for PTT are obtained during the cold crystallization instead of the spherulites formed in the melt crystallization. Second, the edge-on lamellar orientation in thin films is identified during the cold crystallization. The thickness and the lateral width of rod-like lamellae get larger and larger with increasing crystallization temperature. Thin lamellar crystals assemble randomly when the cold-crystallization temperature is lower, while lamellar stacks composed of thicker lamellae are observed when the PTT was annealed at elevated temperature. Moreover, for the cold-crystallized PTT, the final melting temperature does not vary with the crystallization temperature. This phenomenon is explained by the structural improvement during the heating process. For the cold-crystallized PTT sample at lower temperature, three transitions occur when it is heated again: the relaxation of the rigid amorphous phase, the reorganization of molecules in the intermediate phase, and then the melt–recrystallization behavior. Those transitions finally lead to thicker lamellae besides a higher crystallinity before the final fusion. Therefore, the final melting peak of these lamellae is at the same temperature.     

Small angle X-ray scattering studies of poly(ethylene terephthalate) and poly(butylene terephthalate)

Summary Small angle X-ray studies and density measurements were carried out on isotropic PET and PBT samples. PET samples were crystallized between 60 and 260 °C, and PBT between 60 and 225 °C. The aim of these studies was to investigate the dependence of the amorphous density, the degree of crystallinity and the average transmission path through the regions of the two-phase system on the crystallization temperature. It could be shown that PET and PBT crystallize with sharp phase boundaries.Since for the evaluation of the amorphous density the knowledge the exact crystal density is very important, additional measurements of the wide angle X-ray behaviour were made. Both the crystal and the amorphous densities of PET and PBT show specific differences dependent on the crystallization temperature, which can be explained by the higher mobility of the PBT chain.The degrees of crystallization, evaluated with the individual values of crystal density and amorphous density determined on each sample, are principally higher than those calculated with the usually used values of crystal and amorphous density. Investigations of the background scattering have shown that both the specific amorphous and specific crystalline scattering background are constant.For PET and PBT the average transmission path through the amporhous regions firstly decreases with increasing crystallization temperature. This can be explained by new formation of crystallites. At higher crystallization temperatures increases. The average transmission path through the crystalline regions increases over the whole range of crystallization temperature.

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Zusammenfassung An isotropen PET- und PBT-Proben, kristallisiert bei Temperaturen zwischen 60 und 260 °C bzw. 60 und 225 °C wurden Röntgenkleinwinkel- und Dichtemessungen durchgeführt, mit dem Ziel, die amorphe Dichte, die Volumenanteile und die mittleren Durchschußlängen durch die Phasen in Abhängigkeit von der Kristallisationstemperatur zu bestimmen.Da für die Bestimmung der amorphen Dichte die Kenntnis der genauen Kristalldichte sehr wichtig ist, wurden zusätzliche Röntgenweitwinkelmessungen durchgeführt.Es konnte gezeigt werden, daß sowohl PBT als auch PET mit scharfen Phasengrenzen kristallisiert.Die Kristalldichte und die amorphe Dichte von PET bzw. PBT zeigen in Abhängigkeit von der Kristallisations-temperatur spezifische Unterschiede, die durch die höhere Beweglichkeit der PBT-Kette erklärt werden können.Die Kristallisationsgrade, die mit den von uns bestimmten Kristalldichten und amorphen Dichten ermittelt wurden, liegen generell höher als die mit den bekannten Werten von _c und _a berechneten. Untersuchungen des Streuuntergrundes zeigten, daß sowohl der spezifische amorphe als auch der spezifische kristalline Streuuntergrund konstant ist.Bei PET und PBT nehmen die mittleren Durchschußlängen durch die amorphen Phasenanteile bei geringen Kristallisationstemperaturen ab, was durch die Neubildung von Kristalliten erklärt wird, und nehmen bei höheren Kristallisationstemperaturen wieder zu.Die mittleren Durchschußlängen durch die kristallinen Phasenanteile nehmen über den gesamten Temperaturbereich zu.

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With 22 figures and 3 tables     

Model polyurethane networks prepared from poly(ethylene oxide) and poly(tetramethylene oxide)

Polyurethane elastomers of known degrees of cross-linking were prepared from hydroxylterminated poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) chains having numberaverage molecular weights in the range 880–6820 g mol^?1. The chains were end-linked into “model” trifunctional networks using a specially prepared aromatic triisocyanate. The networks thus obtained were studied with regard to their stress-strain isotherms in both the unswollen and swollen states, in elongation at 25°, and with regard to their equilibrium swelling in benzene at 57.9°. Values of the modulus in the limit at high deformation were in good agreement with corresponding results previously obtained on trifunctional networks of poly(dimethylsiloxane) (PDMS). Since PEO has a much higher value of the plateau modulus in the uncross-linked state, this agreement indicates that inter-chain entanglements do not contribute significantly to the equilibrium modulus of an elastomeric network. These values of the high deformation modulus are also in good agreement with recent molecular theories as applied to the non-affine deformation of a “phantom” network. The swelling equilibrium results were in very good agreement with the new theory of network swelling developed by Flory.     

Photolysis of poly(ethylene terephthalate)

The photolysis of poly(ethylene terephthalate) films was studied in vacuo with light of wavelengths 2537 and 3130 A. A very stable filter system which cuts out the 3025 A. line was developed to isolate 3130 A. from a mercury spectrum. Despite the fact that the penetration of 2537 A. light was limited to a depth of a ca. 10³ A. whereas 3130 A. light was more uniformly absorbed it was possible to demonstrate that the quantum yields for CO and CO₂ formation were in agreement for the two wavelengths. Quantum yields for fractures and crosslinks were estimated by sol-gel analysis. An absorption maximum which develops near 13 μ after exposure of poly(ethylene terephthalate) to light or γ-rays was attributed to the formation of groups formed by elimination of CO and CO₂. ESR spectra for trapped radicals were tentatively assigned to the components p-C₆H₃· and ·O? CH₂? CH₂? . It is suggested that the former radicals combine to form crosslinks. Quantum yields (× 10⁴) with 3130 A. light are: CO, 6; CO₂, 2; crosslinks, 5.5; trapped radicals, 1.5; With 2537 A. light, quantum yields are: CO, 6–9; CO₂, 2–3; the network formed was not characterized as to crosslinks and fractures; trapped radicals were observed to exist but not determined.     

Chemical recycling of polyesters. One-pot-two-step conversion of poly(ethylene 2,6-naphthalenedicarboxylate) and poly(tetramethylene terephthalate), producing the corresponding hydroxamic acids and hydrazides

Convenient one-pot-two-step processes for chemical recycling of commercially available polyesters were conducted to produce the corresponding hydroxamic acids and hydrazides in high yields. Glycolysis of poly(ethylene 2,6-naphthalenedicarboxylate) in diethylene glycol into the corresponding oligomers, followed by aminolysis with hydroxylamine and hydrazine yielded 2,6-naphthalenedicarbohydroxamic acid in 96% and 2,6-naphthalenedicarbohydrazide in 85% overall yields. In a similar manner, terephthalohydroxamic acid and terephthalohydrazide were produced in 92 and 91%, respectively, from degradation of poly(tetramethylene terephthalate).     

The heat of fusion of poly(ethylene terephthalate)

By use of the Clapeyron equation for the dependence of the melting point on pressure, the heat of fusion was found to be 32.5 cal/g, in good agreement with values determined by other methods. An equation for the dependence of the melting point on the degree of polymerization gave a heat of fusion of 27.6 cal/g when applied to hydroxyl-terminated oligomers. This simple relation applied all the way down to the smallest member of the series, di(hydroxy ethyl) terephthalate.