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Amorphous samples of polyethylene terephthalate were stretched with different rates and stretching ratios at different temperatures. Afterwards they were crystallized. The arrangement of the crystals and the conformations of the chains in the noncrystalline regions were investigated by means of X-ray wide-angle scattering, X-ray small-angle scattering, birefringence measurements and nuclear magnetic resonance measurements. The influence of the morphological structure on the mechanical strength was determined. The stretching ratio itself generally does not characterize the orientation state. The structure obtained after crystallization depends mainly on the birefringence of the sample after stretching before crystallization. With increasing birefringence one obtains all intermediate structures starting from the well known spherulites composed of twisted lamellae in the unoriented material up to a paracrystalline lattice of lamellae split up into mosaic blocks in the highly oriented state. Also the conformations of the chains in the noncrystalline regions are influenced by the stretching. With increasing orientation the amount of tie molecules with comparatively large end-to-end distances becomes larger. The improvement of the mechanical properties with stretching is caused not only by the increasing orientation of the molecules but also by the increasing amount of taut tie molecules.

Density, heat of fusion and melting temperature data of annealed polyethylene single crystals suggest the existence of a temperature-dependent pseudo-amorphous surface layer which contains chain folds and free chain ends. In the ideal two-phase model, one assumes two such amorphous layers of thickness l/2 each on the two (001) surfaces of the crystalline core of thickness D = L -l, where L is the total thickness of the single crystal. The thickness of such a layer was calculated under the assumption of random length loops and cilia (free chain ends) for the case of adjacent reentry and of a Maxwellian distribution of loop width. The excess energy requirement of the shortest loops with the high concentration of gauche conformations favors longer loops and hence increases the surface layer thickness. The reduction of entropy by the restrictions imposed by finite loop width and the availability of a half space only acts in the opposite direction. The calculated thickness depends on the true supercooling ΔT = Tm° - T if L is kept constant and on relative supercooling ΔTrel = Tm-T, where Tm is the actual melting point of the crystal, if the crystal core thickness D is kept constant. A qualitative agreement between theory and experiment on this basis seems possible by proper consideration of the contribution of loops and cilia.

Investigations of the glass transition and melting of partially crystalline polymers by nuclear magnetic resonance provide valuable information on the nature of noncrystalline regions. The broad line NMR signal was separated into a narrow component and a broad component by using a new method which does not imply the ambiguity usually present. From the intensity of the narrow component the mobile fraction was determined. This fraction was extrapolated to “infinite” temperature. By subtracting the mobile fraction from the noncrystalline fraction, the noncrystalline rigid fraction was obtained. Comparison of the measured second moments of the two components of the NMR line with calculated second moments of chains with fixed ends shows the following: The mobile fraction is formed by chains with either one end fixed or both ends fixed in a comparatively small end-to-end distance (for example, loops with adjacent reentry); the noncrystalline rigid fraction is formed by chains whose ends are fixed in a comparatively large or medium end-to-end distances (for example, tie molecules connecting different crystals). More detailed information on the chains forming the mobile fraction as well as on the structure in the melt was obtained by high resolution NMR. It was shown that near range order in the melt, for example, the formation of bundles of parallel chains, causes deviations from the lorentzian shape of the NMR line. During primary crystallization the chains within the bundles of parallel chains crystallize. During secondary crystallization, extremely mobile chains outside these bundles are incorporated into the crystals.

Measurements of wide-angle diffraction during high speed spinning of poly(ethylene terephthalate) (PET) have been performed using synchrotron radiation. The experimental set-up has been improved so that it became possible to determine the degree of crystallinity, crystallite orientation and fiber diameter along the spin line. For take-up speeds of 3600 m/min and higher, the crystal reflections appeared at a distance of 40 cm from the spinneret, just after the necking region. The crystallization speed increases proportional to increasing take-up speed. For the take-up speeds investigated, this results in a constant crystallinity profile when measured as a function of the distance from the spinneret. The final fibers exhibited an extraordinarily high degree of crystallinity, which has been attributed to the high molecular weight of the polymer. Below 3500 m/min, no crystallization and no necking could be detected up to a distance of 90 cm from the spinneret. The results showed that necking and crystallization were closely coupled. No orientation of the amorphous matrix prior to crystallization could be detected by means of X-ray diffraction. Moreover, the orientation of the crystallites was constant along the spin line.

Simultaneous measurements of small- and wide-angle X-ray scattering (SAXS and WAXD) were performed during the melt spinning of isotactic poly(propylene). The extruder assembly was mounted on a platform, which could be moved horizontally and vertically allowing variations of the measuring point between distances of 28 and 90 cm from the spinneret. The SAXS and WAXD pattern were taken simultaneously with two two-dimensional detectors. Additionally, the fiber diameter profile was measured. The development of the crystallization and the orientation of the crystallites were studied as a function of the distance from the spinneret. The wide-angle data revealed that highly oriented crystals grow out of an apparently unoriented amorphous matrix. Moreover, the orientation of the crystallites was found to be constant along the spin line. Both crystalline WAXD and SAXS peaks were found to occur at the same distance from the spinneret within the resolution of the apparatus. A comparison of WAXD and SAXS shows that the crystallization and the formation of a superstructure follow the same kinetics.

6 pags., 4 figs., 1 tab., Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190-260 °C) for different times (10 min-24 h) in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10000-120000). Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, Hc PET = 405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30000. It is shown that the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity, crystal thickness) which is formed at given heat treatment conditions. © Steinkopff Verlag 1998., The authors are grateful to DGICYT, Spain (Grant PB94-0049) for the support of this investigation. The partial support of DFG, Germany (Grant DFG-FR 675/21-1) is also highly appreciated. Part of the work is performed in the frame of the Partnership Contract between University of Hamburg and University of Sofia. One of us (S.F.) deeply appreciates the tenure of a sabbatical grant from DGICYT

The miscibility of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) with poly(butylene terephthalate) (PBT) has been studied by 13C CP/MAS NMR complemented with DSC measurements. The blends were prepared by a solution precipitation method. The DSC examination shows that the Tg of the blends is between the Tg of the two homopolymers. The crystalline enthalpy of PEN decreases continuously when the amount of PEN decreases. The Tm and ΔHm of PBT were lowered continuously as the PEN ratio was increased, while that of PEN was lowered as the PBT ratios were increased. These results imply that PEN is compatible with PBT. HT1ρ values for the blend 50 PEN/50 PBT and pure components have been measured. Since single-component NMR relaxation behavior was observed, miscibility was demonstrated for the blend. Intermolecular cross polarization from the protons in PBT to carbons in deuterated PEN was examined by measuring the full decoupling, no decoupling, and delayed decoupling 13C CP/MAS spectra of the blends of deut...

Selectively deuterated poly(ethylene-2,6d-naphthalene dicarboxylate) (PEN) was synthesized, obtaining a material in which either the ethylene groups (PEN-Ed1 or the naphthalene ring (PEN-Nd6) was deuterated. By means of deuteron nuclear magnetic resonance (2H-NMR), the molecular mobility of the deuterated groups was investigated as a function of temperature. The spectra were measured by the solid echo method, applying different waiting times tw The longitudinal relaxation curves were obtained by determination of the maximum intensity of the echo as a function of tw It was found that in the amorphous regions of PEN, the molecular mobility of the ethylene groups is higher than in the amorphous regions of PET. In PEN crystals in the β-modification form, trans-gauche jumps of the ethylene groups with almost equal occupation of the trans and the gauche conformation take place already at 90°C. This is not the case in either PEN crystals in the a-modification form or in PET crystals. The rotational moti...

The common crystallization conditions of poly(ethylene terephthalate) (PET) were replaced by an anabaric high-pressure crystallization at 320 °C. The PET samples were characterized by differential scanning calorimetry, density and microhardness. The resulting two-phase microstructure was studied by means of absolute small-angle X-ray scattering (SAXS). A complete SAXS analysis utilizing the interface distribution function (IDF) method was carried out. The resulting structure exhibited the presence of stacks of 10 nm thick crystalline lamellae which were separated by amorphous layers of about 1.3 nm thickness. Similar structures have been found after annealing of amorphous metals and have been termed nanocrystalline. Microhardness and structure have been discussed in analogy with the notions from the field of nanostructured materials. Theoretically, a multi-component lamellar two-phase structure has been discussed. The equations derived allow the computation of volume fractions and specific surfaces of the components (different kinds of stacks).

An experimental set-up in the synchrotron radiation beam was constructed for performing wide angle X-ray scattering (WAXS) on-line measurements, during high speed spinning of poly(ethylene terephtalate) (PET). In order to detect the very weak scattering of the thin filaments (= 26 μm diameter) the capton windows of the vacuum tubes were removed and the air was replaced by helium. In this way it became possible to measure the development of crystal reflections as a function of the distance from the spinneret. A comparison of the results with corresponding on-line measurements of the fibre diameter indicates that crystallization starts at the beginning of the necking zone.

Two different etching techniques that reveal the semicrystalline morphology of polyesters have been developed and applied to an analysis of the phase structure of copolyesters made by reacting poly(hydroxybenzoic acid) (PHBA), and poly(ethylene naphtha-lene-dicarboxylate) (PEN). One technique is based on oxidation with acidic permanganate solutions and is used to study the macroscopic distribution of different phases. The other is based on sa-ponification with alkaline reagents and reveals more detailed structure within the various phases. Etching and electron microscopic examinations have been carried out for three different PEN-co-PHBA compositions. Three different types of solid phase are revealed: (1) a phase rich in PEN; (2) a phase containing roughly equal proportions of the two components, liquid crystalline at high temperatures; (3) a solid phase of crystalline HBA-rich molecules, which segregate into laminar regions. These observations are consistent with the previously published thermal...

Most polymers crystallize by a nucleation-and-growth mechanism in which spherulites develop as a consequence of the radial growth of branching crystalline lamellae from heterogeneous nuclei. The amorphous component is included within the spherulites. These grow until they impinge and become volume filling. The primary crystallization occurs at the expanding interface of the spherulite with the amorphous polymer. Secondary crystallization may sometimes occur within the spherulite. Spherulite growth kinetic is often followed microscopically. The small-angle light scattering technique developed in our laboratory [1] has proved to be a conveient method for quantitatively following spherulitic crystallization. It can provide information about the number and sizes of spherulites as well as their internal crystallinity.

The high-resolution solid state 13C NMR spectra of the different crystal modifications of poly(4-hydroxybenzoate)s and their copolymers have been obtained by means of high-power proton decoupling, cross-polarization, and magic angle spinning. The resolution was sufficient in order to resolve the resonance lines of all seven differently bonded carbon atoms in the PHBA repeat unit. From the chemical shift splitting of the ortho ring carbon atoms it is deduced that, in crystalline PHBA, the torsional angle between the ester plane and the phenylene ring plane deviates from 90°. The deviation increases in the order modification II > modification III > modification I. The variable-contact-time measurements indicate that the chain packing in crystal modification I is denser than in the crystal modification II.

We have examined the micro indentation hardness of a series of carbon fiber reinforced epoxy and thermoplastic polyimide (TPI) composites. In the epoxy systems, the influence of Nylon particles was studied. The effect of crystallization of the thermoplastic polyimide upon the microhardness values of the resin was also investigated. The microstructure of the TPI-composites was characterized by X-ray diffraction. The results show that the addition of carbon fibers to the neat resins greatly increases the microhardness and thus the yield stress of the composite. The value of the microhardness technique is highlighted in emphasizing the heterogeneity of the CFRC.

This paper reports the effect of solid state annealing on the structure of a liquid crystalline polymer composed of 80% 4-hydroxybenzoic acid (HBA) and 20% 2-hydroxy-6-naphthoic acid (HNA) using small-angle X-ray scattering. Two-dimensional diffraction patterns possessing strong meridional reflections were recorded using synchrotron radiation at temperatures of 215, 251 and 269°C. The long period increased with increasing anneal temperature, but was largely unaffected by increasing the length of time spent at the anneal temperature. The intensity of meridional scattering increased with both increasing anneal temperature and time. In order to obtain an estimate for the average crystallite thickness at the anneal temperature, the small-angle meridional scattering was evaluated by means of the interfacial distribution function approach.

A microfocus camera with a focus of 7 μm fwhm and a flux of 10 11 photons/s at the ESRF in Grenoble was used to investigate the microstructure of liquid crystalline polymer samples of 4-oxybenzoate-co-6-oxy-2-naphthoate (73 :27) (Vectra A950 from Hoechst-Celanese). These samples show isotropic scattering when examined by means of a conventional X-ray camera with a large focus (2 mm). In melt-pressed thin films, we observed local variations of the direction of molecular orientation, which is due to the presence of disclinations. Except at the center of the disclinations, the order parameter is nearly constant within the scanned area. In samples cut out of the center part of an injection-molded bar, we detected a four-point scattering pattern due to a zigzag chain conformation.

9 pags., 11 figs., Amorphous poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) films (∼ 220 μm thick), stored in ambient atmosphere for different periods of time and after annealing at different temperatures below T = 123°C, for different times, have been investigated by infrared spectroscopy (FTIR), microhardness, and differential scanning calorimetry (DSC). FTIR spectroscopy and weight measurements reveal the presence of water which is easily removed by annealing of the films. Films again recover their initial weight and absorption bands after 1‐2 days storage in ambient atmosphere. Samples annealed at different temperatures T for different times t show an increasing microhardness for relatively short times of t. The microhardness passes through a maximum at an annealing time depending on T, and it decreases toward values somewhat larger than the initial ones. The changes observed in the microhardness and in the values of the excess enthalpy with storage time of the samples at room temperature depend on the physical aging as well as on the content of water of PEN films. © 1995 John Wiley & Sons, Inc. Copyright © 1995 John Wiley & Sons, Inc.

A study of the phase structure of two linear polyethylene fractions has been carried out by Raman spectroscopy and from the analysis of the interface distribution function from the SAXS intensity data. Very good agreement is obtained for the core crystallite thickness, the liquid-like region, and the thickness of the interface from these two independent techniques. Moreover, the X-ray analysis distinguishes isothermally formed crystals from quenched crystals in cases where the Raman technique is not selective.

10 pags., 5 figs., The 4000–2000 cm infrared spectral region from transmission FTIR spectra of films (≈ 220 μm thick) of amorphous poly (ethylene terephthalate) (PET) and poly(ethylene 2, 6‐naphthalenedicarboxylate) (PEN) was analyzed. In addition to the strong bands for the stretching vibration modes of H‐C bonds, the ester‐overtone band at about 3430 cm and a doublet (3630, 3550 cm) band, related to absorbed water, appear. The spectra for these materials show significant differences in absorptivity and frequency for the ester overtone band. Real time water sorption/desorption in these films was investigated simultaneously by FTIR spectroscopy and by measurement of weight changes. A linear correlation between the integrated absorbance of the water bands and the relative weight variation of the films was found for these two polymers. Results show that the infrared absorptivity of these bands is identical in both materials and that water molecules are weakly bound to ester groups throughout the films. However, it turns out that the water content is higher in the case of PEN which has a larger specific volume. Copyright © 1995 Hüthig & Wepf Verlag

Using synchrotron radiation, one is able to measure the small angle X-ray scattering (SAXS) and the wide angle X-ray scattering (WAXS) of polymers within seconds. Thus one can follow in real time the change of scattering during crystallization, melting, and stretching, as well as during different kinds of processing. We have built up at HASYLAB in Hamburg a beamline dedicated to investigations of phase transitions in polymers. Besides a furnace, a goniometer and a stretching device one can also insert into the beam an extruder for investigating the fiber spinning process. We have performed simultaneous measurements of WAXS and SAXS during crystallization and melting of polymers. Three different mechanisms of secondary crystallization were identified: growth of crystals, formation of new crystals and formation of new lamellar stacks. Interesting results were obtained for the crystallization of highly oriented polymers during melt spinning. Here a SAXS pattern appears before WAXS crystal reflections are visible, indicating that two phases with different densities have been formed before any crystalline order can be detected. By means of SAXS during stretching of blockcopolymers of styrene-butadiene-styrene the dimensions and the increasing orientation of the styrene cylinders were determined.

Through the use of a high intensity synchrotron X-ray source and a specially constructed X-ray transparent flow cell, the feasibility of monitoring phase transformations in situ within the extruder has been demonstrated. Specifically, in the present experiments on polyethylene the emergence of a new, flow-induced phase was noted at around 150°C arising in the capillary portion of the rheometer consistent with the hexagonal crystal form of polyethylene. This ‘mobile’ mesophase would account for the recently discovered rheological melt flow singularity (the ‘extrusion window’) occurring at 150°C in agreement with previous hypotheses.

The microhardness (H) of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) with a wide range of crystallinities, spherulitic morphologies and different lamellar periodicities has been determined. The influence of the temperature and time of crystallization from the glassy state upon the microhardness values has been examined. For structures where primary crystallization is incomplete, it is shown that H increases linearly with the volume fraction of spherulites. For materials where primary crystallization is completed, H depends on the crystallization temperature and appears to be a function of both the crystallinity and the crystal size. The results are discussed in the light of theoretical predictions of hardness.

The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180°C are less perfect and the lamellar stacks in...

The melting and recrystallization of yarns of polyamide 6 spun at different take-up velocities ranging from 3 500 to 5 600 m/min was investigated by means of wide-angle X-ray scattering (WAXS) employing synchrotron radiation and by differential scanning calorimetry (DSC). It was shown that the first peak in the double melting peak of the DSC-curves is caused by the melting of the γ-crystals. The melting point is increased by approximately 5°C when the take-up velocity is increased from 3 500 m/min to 5 600 m/min. The addition of calcium stearate to the material has no effect on the thermal stability of the crystals, but seems to have some effect on the crystallization rate.

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.

Selectively deuterated ternary copolyesters of poly(ethylene terephthalate)(PET), poly(ethylenenaphthalene-2,6-dicarboxylate)(PEN) and poly( p -hydroxybenzoic acid) (PHBA) showing the molar composition 35:35:30 were synthesized. In these copolyesters the liquid crystalline state, as well as the isotropic state, can be frozen in by quenching the material from different temperatures. In this way it is possible to compare the molecular mobility in both states. By means of dynamic mechanical analysis it was shown in previous investigations that the glass transition temperature, T g , of the liquid crystalline state is about 35°C lower than that of the isotropic state. The molecular mobility of the ethylene groups and of the phenylene rings below and above T g in both the liquid crystalline and the isotropic state is now investigated by means of deuteron n.m.r. It is shown that the trans-gauche jumps of the CH 2 groups in the elongated chains in the liquid crystalline state can occur at lower temperatures than in the coiled chains in the isotropic state. As a consequence, the fraction of flipping phenylene rings in the liquid crystalline state is larger than in the isotropic state, when compared at the same temperature.

The scattering behaviour of polyetherester thermoplastic elastomers based on polybutylene terephthalate as hard segments and polyethylene glycol ( Mn = 1000) as soft segments in a ratio 49/51 wt.% is studied under stress. Drawn (λ = 5) bristles are annealed with fixed ends in order to create a standard initial structure. Samples with structure destroyed by additional drawing as well as with structure regenerated by solid-state reactions or chemical crosslinking are prepared. The data from small-angle x-ray scattering (SAXS) taken under or without stress are evaluated using Stribeck's method and the sizes of crystalline (d 1) and amorphous (d 2) regions are directly obtained. A constant value of d 1 ≊ 50 A is found for all samples except for the chemically crosslinked one, for which d 1 changes at deformations higher than 80% due to axial displacement of the crystallites. The size of the amorphous regions d 2 measured under stress (e > 30-50%) rises slightly and reversibly followed by a drop simil...

The kinetics of the microphase separation transition in a diblock copolymer of polystyrene/polyisoprene was studied with time-resolved small-angle X-ray scattering. Using synchrotron radiation it was possible to determine the structure factor in time intervals of 10 s. The relaxation of the structure factor after temperature jumps within the disordered regime was found to be wave vector dependent in accordance with Cahn-Hilliard theory. For quenches from the disordered into the ordered state an additional, slow process was found which consists mainly of a decrease in the width of the first-order reflection. It is interpreted as the perfectioning of the lamellar order. Whereas the corresponding relaxation time had been found to decrease strongly with supercooling for shallow quenches, it is found to increase again for deeper quenches.

Experimental equipment was constructed for simultaneous measurements of wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) using synchrotron radiation as a strong source of X-rays. The crystallization occurring during heating of an initially amorphous sample with constant heating rate was investigated. Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN), poly(ethylene terephthalate) (PET) and the copolymer PEN-co-PHB (90:10), where PHB stands for poly(p-hydroxybenzoic acid), were used as materials. By comparing the change of the degree of crystallinity as measured by WAXS and DSC with the change of the SAXS power Q, it was shown that the primary crystallization, during which morphological units like spherulites axe growing, is followed by a secondary crystallization during which the degree of crystallinity with the lamellar stacks in the spherulites is increased. Assuming a two-phase system for the semicrystalline structure, consisting of crystals and amorphous regions, three different processes were shown to be responsible for this increase: The formation of new crystal lamellae within the already existing lamellar stacks, the thickening of already existing crystals at the expense of the amorphous regions, and the complete melting of crystals followed by formation of new, thicker, crystals.

Samples of poly(ether ether ketone) (PEEK), poly(ether ether ketone ketone) (PEEKK), and poly(ether ketone ether ketone ketone) (PEKEKK) were crystallized at different temperatures by stepwise cooling from the melt to obtain samples which show multiple melting peak in a calorimetric investigation. The melting behavior of these materials was investigated by WAXS and SAXS and by DSC. The change of the degree of crystallinity, of the SAXS power Q, and of the long period was determined as a function of temperature during heating. It was concluded that( the additional meltiong peaks are caused by muelting of some thin crystals within lamellar stacks and not by melting of complete lamellar stacks

Copolyesters of poly(tetramethylene terephthalate) (PTMT) and p-hydroxybenzoic acid (PHB) are obtained by means of transesterification in the molten state using different ratios of the starting reagents. After treatment with trifluoroacetic acid, the total reaction product could be divided into a soluble part and an insoluble one, differing in the tetramethylene terephthalate/oxybenzoate (TMT/OB) units ratio. It was proved by 1H NMR that the fraction of OB units in the soluble part of the copolyester varies from 3 to 12 mol-% for PHB feed contents of 10–80 mol-%. There is no systematic influence of the PHB feed content on the copolyester composition. The maximum OB content was achieved at 20 mol-% PHB in the starting mixture. The results from 13C NMR, DSC, WAXS and crystallization kinetics measurements suggest the presence of blocks of TMT units in the macrochains. The observed thermal properties and crystalline structure are explained in terms of the inhomogeneity of both chemical composition and units sequence in the total reaction products. This leads to the coexistence of at least two phases differing mainly in their content of OB units.

On-line small-angle and wide-angle x-ray scattering experiments were performed during the melt spinning of polyvinylidene fluoride using the DESY synchrotron light source. In these studies, the melt-spinning apparatus consisting of a screw extruder, a metering pump, and a take-up motor system were assembled on two separate stepper-motor-driven platforms. To investigate the structure development during crystallization, the tape location at the desired distance from the die could be positioned at the beam level with synchronous vertical movement of extruder and take-up platforms

Copolyesters of poly(ethyleneterephthalate) (PET), poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) and poly(p-hydroxybenzoate) (PHB) form liquid crystalline (LC) phases if the fraction of PHB is larger than about 30%. In some of these copolyesters the liquid crystalline state as well as the isotropic state can be frozen in by quenching the material from different temperatures. This makes it possible to compare both states with each other. By means of dynamic mechanical analysis it is demonstrated that the glass transition temperature Tg of the LC-state is about 30°C lower than that of the isotropic state. Neutron scattering measurements show that the radius of gyration of the molecules in the LC-state is larger than for molecules in the isotropic state. The molecular mobility below and above Tg in both the LC and the isotropic state is investigated by means of deuteron NMR.

The WAXS pattern of the continuous carbon fiber-reinforced laminates can be viewed as a superposition of the scattering patterns arising from the carbon fibers and the polymer matrix. In order to obtain the scattering of the matrix alone, the scattering of the pure reinforcing fibers has been measured at different azimutal angles. A procedure has been developed to substract the scattering of the fibers from that of the complete laminate. From the corrected diagrams, the decree of crystallinity has been determined. Crystallinefractions of 0.46 and 0.34 have been obtained for the PET and the PEEK-based laminates, respectively.

Cross-polarization/magic-angle spinning 13 C nuclear magnetic resonance measurements on blends of poly(ethylene terephthalate) (PET), poly(ethylene naphthalene dicarboxylate) (PEN) and copolyesters of PET and p -hydroxybenzoic acid (PHB) were performed using different dephasing times of the dipolar decoupling. In the case in which the spectra of the two components of the blends are different, information on miscibilities is obtained by measurements with full dipolar decoupling. In the case of similar spectra, however, this method cannot be applied. It is shown that, under this condition, information on phase separation is obtained if the measurements are performed with delayed decoupling and no decoupling. While blends of PEN and copolyesters of PEN are miscible, phase separation is obtained if one component contains PEN and the other one PET.

Semicrystalline poly(ethylene terephthalate) was hydrolysed in water at 180°C under elevated pressure and subsequently treated with ethanol, following the etching process first developed by Miyagi and Wunderlich. The weight loss, the wide-angle X-ray scattering and the molecular weight were measured as a function of etching time. It was found that even at the end of the etching process not all the amorphous material could be removed by the hydrolysis treatment. By comparing the obtained results with those derived from an elaborate small-angle X-ray scattering study and with wide-angle X-ray scattering measurements, it was concluded that only those amorphous regions lying outside of the lamellar stacks were removed. Subsequently, the lamellar stacks themselves were attacked. It was also found that at the very beginning of the hydrolysis process additional crystals were formed in the material.

Samples of poly(acrylonitrile) which were deuterated in the α-position (PAN-α-d 1 ) and in the β-position (PAN-β,β-d 2 ) were heated from room temperature to 180°C. The longitudinal relaxation curves and the NMR spectra of the deuterons were measured as a function of temperature. It was found that the longitudinal relaxation curve could be separated into two exponential curves. The traction of the component showing the larger relaxation time T 1 decreased with increasing temperature. The shape of the NMR spectra changes from a Pake spectrum at room temperature to a spectrum typical for rapid crankshaft motion at 180°C

The isothermal crystallization of linear polyethylene fractions was studied by means of simultaneous measurements of wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) employing synchrotron radiation. From WAXS the overall degree of crystallinity xc was determined. From SAXS, the scattering power Q was evaluated and compared with several different models for the crystallizing system. When the scattering arises solely from the supermolecular structures, such as spherulites, Q is proportional to xs·xcL·(1 − xcL), where xs is the fraction of material transformed into such structures and xcL is the degree of crystallinity within these structures. By comparing xc with Q it was possible to separate the primary and secondary crystallization and to show that secondary crystallization takes place within the lamellar stacks where the crystals become thicker and the amorphous layers become thinner. The process of recrystallization during annealing of crystalline samples was studied in the same way. Other models were treated in a similar manner.

Oriented liquid-crystalline solutions of the rigid heteroaromatic polymers poly( p -phenylene benzobisthiazole) and poly( p -phenylene benzobisoxazole) in polyphosphoric acid were transformed into crystalline phases by absorption of moisture. At moderate moisture levels crystal-solvate phases are formed by co-crystallization of the polymer and its solvent, whereas at high water content the crystalline polymer phase is formed by deprotonation of the polymer. Two crystal-solvate forms have been identified, as the moisture content increases up to about 10% (w/w), denoted form I and form II. Transitions between the different phases, as a function of temperature and time, were studied by X-ray diffraction using the high-intensity synchrotron source. The intensity of the crystalline reflections from the form I state decrease gradually with increasing temperature up to final melting at about 70°C. The orientation of the crystalline phase is maintained up to its melting. Recrystallization is observed upon quenching, showing the reversibility of this transition. The behaviour of the form II phase differs markedly. As the temperature is increased, a gradual crystal-crystal transition occurs in the temperature range of 250–300°C from the form II state to the crystalline polymer state. This transformation is irreversible. A novel recrystallization phenomenon is observed when the liquid-crystalline phase is heated to about 250°C. Crystalline reflections appear at spacings close to those of the crystalline polymer state. These reflections disappear upon cooling. These transformations are discussed in terms of the state of protonation of the polymer in its solution in polyphosphoric acid. Form I is considered a complex of the protonated polymer and the acid anions, which dissolves at moderate temperatures. Recrystallization at elevated temperature is suggested to result from deprotonation of the polymer. The state of protonation of the polymer in the form II state is still not understood.

Thermoanalytical measurements and tack tests were both performed using a commercially available carbon fiber/epoxy prepreg system (Hercules 3501–6) to examine changes caused by aging as they affect handling and processability of thermosetting matrix-based composites. Combining these techniques, a relationship between prepreg bulk and surface characteristics in relation to aging was investigated. Isothermal kinetic studies at low temperatures showed maximum conversions (αm) that increased with increasing cure temperatures. In addition, a linear relationship between glass transition temperatures (Tg) and conversions (α) was observed regardless of aging (or cure) temperatures. Energy of separation of prepreg stacks, which may be viewed as a measure of prepreg tack, showed a maximum value at a specific temperature. The maximum energy of separation was observed in the temperature range of 20–25°C above the glass transition temperature for a given sample. However, the maximum energy of separation values decreased with increasing aging times (or conversions), implying that prepreg tack was a viscoelastic property rather than a viscous property of the resin matrix in the prepreg.

The molecular orientation in poly(ethylene terephthalate) (PET) drawn by necking was studied before and after crystallization by 2 H nuclear magnetic resonance (n.m.r.) and by wide-angle X-ray scattering (WAXS) pole figures. In order to determine separately the orientation of the benzene ring and of the ethylene groups, the n.m.r. investigations were performed on samples in which only the benzene ring was deuterated as well as on samples in which only the ethylene groups were deuterated. By applying different ‘waiting times’ in the n.m.r. measurements, it was also possible to determine separately the orientation of chains of different mobilities. Thus, more detailed and more complete information on molecular orientation is obtained by n.m.r. than by WAXS. As far as a comparison was possible, agreement between n.m.r. and WAXS was obtained. In addition, the n.m.r. results show that, for example, a parallelization of the planes of the benzene rings occurs not only in the crystals but also in the amorphous regions, and that the ethylene groups are oriented to a smaller degree in the draw direction than the benzene ring parts of the chain.

Blends of deuterated and nondeuterated copolyesters of poly(ethylene terephthalate) (PET) and poly(p-hydroxybenzoic acid) (PHB) were studied, the PET content varying between 80 and 60 mol% and the sample containing 60 mol% being liquid crystalline. The molecules contained deuterated and nondeuterated blocks of various lengths. The average degree of polymerization and radius of gyration of these blocks were measured and the length of the statistical element b was calculated as a function of composition. It was concluded that, in the nematic state, the molecules are not elongated

Highly oriented linear polyethylene was prepared by elongational flow injection molding. The changes in crystal orientation were investigated as a function of temperature by real-time wide-angle X-ray diffraction. Additionally, the influence of molecular weight upon the microstructure and the changes in orientation, during heating near the melting point, and after cooling have been examined. A shish-kebab structure is inferred for the high molecular weight samples (Mw≥105) from SAXS observations, while for samples with Mw

Solvent-induced crystallization (SINC) was observed in a polyetherimide (PEI), a thermoplastic used as a matrix in carbon fiber composites. This observation was made using wide angle X-ray scattering (WAXS), differential scanning calorimery (DSC), and optical microscopy. It was discovered that methylene chloride induces crystallization in the PEI by penetrating the surface and swelling the bulk polymer

The change of molecular mobility during the phase transition of PHB/3-C1-PHB copolymer (5:1) from the orthorhombic modification II into an orthorhombic modification which is close to hexagonal chai...

Structural changes in the para-ferroelectric phase transition of the vinylidene fluoride-trifluoroethylene copolymer with 60 40 molar content have been investigated by means of real-time X-ray diffraction. A combined study of (i) long period from small-angle X-ray scattering, (ii) coherently diffracting domains derived from the integral width of the wide-angle reflections and (iii) lattice spacings offers the following picture. In the high-temperature region (65–140°C) the stacks of 250 A thick paraelectric lamellae are found to consist of 250 A wide coherently diffracting blocks. At the Curie transition (65-50°C) a breakdown of the large paraelectric crystals into thinner and smaller ferroelectric domains statistically mixed with the remaining paraelectric zones is observed. In the low-temperature region (T