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Nonisothermal kinetics of smectic phase formation in a chiral liquid crystalline (LC) azodye polymer is studied. The Ozawa exponent value of n ~ 2.5 is estimated for narrow polymer fractions with Mw/Mn ~ 1.3−1.6 but a temerature-dependent value, 0.5 < n < 1.2, for the raw polymer of Mw/Mn ~ 2.6. The effect of molar mass on mesomorphism is studied, and the dependence of melting temperature on subsequent heating from the rate of previous cooling, r, is theoretically explained. The narrow fractions show a “bistable” phase behavior forming conventional Sm A phase on slow cooling, r < 1 K/min, but another (probably a highly twisted TGB A*) mesophase on fast cooling, r > 1 K/min. A theoretical model for such a behavior is suggested, and the structure of the two phases is studied by SAXS. The applicability of the Kissinger approach to estimation of activation energy for TGB A* phase formation is discussed.

Blends of ϵ-polycaprolactone (PCL) and low molecular weight atactic polystyrene (PS) are among those which show an upper critical solution temperature, and where one component (in this case PCL) is crystallizable, leading to several possible competitive interactions between blend decomposition and crystallization. Scanning and transmission electron microscopy have been used to obtain finer morphological information relating to two compositions where this phenomenon has already been followed under the optical microscope. This has been made possible by the development of several etchants which allow inspection of the internal bulk morphology with good resolution. The system 40% PCL–60% PS decomposes binodally to a majority phase with roughly equal proportions of PCL and PS surrounding blobs of a minority phase composed almost entirely of PS. The large spherulites of PCL grow around and engulf the PS-rich blobs. The system 60% PCL–40% PS crystallizes from a homogeneous melt. In this case, as the low molecular weight PS is able to diffuse outward from the growing spherulite, the composition of the remaining melt changes to one which can decompose binodally. TEM shows the PCL lamellae to be separated in bundles, as is found in other blend systems. The PS-rich phase is observed to segregate either at the spherulitic growth front, where it forms small droplets of the order of 1μm in size, or outside the spherulites, where it coalesces into larger droplets, which in bulk specimens ooze to the surface giving a featureless layer largely concealing the spherulitic morphology. Spinodal decomposition has also been observed in melt which has been rapidly quenched in liquid nitrogen and allowed to warm up to room temperature.

The growth of spherulites of poly(ethylene oxide) in blends with poly(hydroxyether of bisphenol A) was investigated. In a very narrow range of crystallization temperatures, the spherulite growth deviates from the usual constant growth rate regime in a systematic manner in which the growth rate decreases with time. This is explained by local and overall changes in the composition with the proceeding crystallization that are due to the competition between the crystallization and diffusional chain displacement rates, respectively. These kinetic phenomena and processes can quantitatively be described by a suitable analysis of the experimental findings. Deceleration is predominantly caused by a slowing of the chain motion by the glass-transition temperature being approached (i.e., vitrification) and, to a lesser extent, by dilution. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1250–1257, 2000

The diffusion constant of water through transcrystalline surface layers on isotactic polypropylene (i-PP) is reported. A suitable experimental technique was developed, based on sorption or desorption measurements. The accompanying change in sample weight is detected by the corresponding change in mechanical resonance frequency. The facility allows investigation of the diffusion current parallel to as well as perpendicular to the sample surface. Tests with commercial polyethylene films revealed that reproducibility and reliability are better than 6%. The samples were prepared as thin films in which the transcrystallinity was controlled by use of several substrate materials and different thermal conditions during solidification of the melt. The water diffusion constant of finely spherulitic i-PP turned out to be 15.9 μm²/s; whereas the values for transcrystalline material amounted to 19.6 μm²/s parallel and between 12 and 10 μm²/s perpendicular to the film surface, depending on the actual supermolecular structure. These results are discussed with respect to the underlying transcrystalline texture and the texture of the amorphous percolation network. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3275–3285, 1999

The type of supermolecular structure and the morphology in binary polymer blends with one crystallizable component and with a miscibility gap are strongly influenced by the relative rate of crystallization and demixing. Depending on the composition of the blend and on the relative position of the crystallization curve and the miscibility gap in the phase diagram, demixing-induced crystallization as well as crystallization-induced demixing can occur. Both these approaches lead to new and interesting structures. Additionally, the interaction of the two mentioned kinds of phase transition can under circumstances affect the growth rates of adjacent spherulites. This results in anisotropic concentration distribution or phase-separation morphology around their surfaces.

The morphology and the crystallization of blends of poly(vinylidene fluoride) (PVDF) with polyamide-6 (PA-6), and with poly(butylene terephthalate) (PBTP), were investigated in detail by electron microscopy and by DSC. In some of the blends, the dispersed component exhibits rather small particle sizes and, followingly, a high number density of the dispersed particles which is in the order of magnitude of, or exceeds the number density of the usually nucleating heterogeneities. In these blends, the crystallization of the dispersed component proceeded in two steps, induced by different nucleating species (“fractionated crystallization”). The nuclei concentrations in the components and the specific interfacial energies of the PVDF nucleation steps were estimated. An unusual type of fractionated crystallization occurs in some cases: matrix and disperse phases crystallize completely coincident due to a specific mutual nucleating efficiency of both components. An estimation of the interfacial energies involved suggests a nucleating activity of PVDF crystals for PA-6. Moreover, a rise of the crystallization temperatures of the PA-6 and PBTP matrix phases is observed that may indicate a migration of nucleating impurities during melt processing from PVDF towards the second component.

Investigations of melting, equilibrium swelling and the stress-strain behavior of radiation crosslinked polyethylene are reported. The results are jointly described where by a novel phenomenological treatment of the swelling of van der Waals networks was needed implicating a discussion as to how the modulus is related to the concentration of the cross-linkages. This concentration is obtained from the analysis of the melting process by application of the thermodynamics of eutectoid copolymers, which is also shown to deliver structural parameters which are in good accord with X-ray data.

Zusammenfassung Es wird über Druck-Stauch-Experimente an Polyoxymethylen bei Raumtemperatur berichtet. Die Struktur der Umformlinge wurde röntgenografisch untersucht; ferner wurde die Relaxationsspannung bei Erwärmung gemessen. Bei kleinen Stauchungen beobachtet man lediglich eine spontan-reversible Deformation der amorphen Matrix des sphärolithischen Ausgangsmaterials. Für ?<0,95 beginnt interlamellare Scherung und Lamellenumorientieren. Später tritt zusätzlich Kettengleiten in den lamellaren Bereichen auf, was im Bereich 0,6>?>0,3 zu einer Scherung in Kettenrichtung {110} [001] führt. Bei noch stärkerer Deformation tritt eine Lamellen-Fibrillen-Transformation auf. Aus Deformations- und Relaxationsverhalten kann auf das Volumen der Mikrokristalle geschlossen werden, die die Knoten eines hypothetischen Netzwerkes darstellen.

A report is given of structural investigations on high molecular weight, highly linear polyethylene crosslinked by irradiation with fast electrons in both the molten and the solid state. For the melt-irradiated samples it could be concluded from X-ray measurements that insertion of lattice distortions of the first kind occurs on crystallization. The density of these distortions shows a distinct maximum for an irradiation dose of 25 Mrad. It is assumed, that for lower doses the material crystallizes according to a folding procedure, for higher doses according to a micellar one. For solid state irradiated samples crystalline structure and morphology are not influenced measurably by the crosslinking. The recrystallization behaviour is independent on the dose for the resulting inhomogeneous network.

Secretory proteins are synthesized with a signal sequence that is usually cleaved from the nascent protein during the translocation of the polypeptide chain into the lumen of the endoplasmic reticulum. To determine the fate of a cleaved signal sequence, we used a synchronized in vitro translocation system. We found that the cleaved signal peptide of preprolactin is further processed close to its COOH terminus. The resulting fragment accumulated in the microsomal fraction and with time was released into the cytosol. Signal sequence cleavage and processing could be reproduced with reconstituted vesicles containing Sec61, signal recognition particle receptor, and signal peptidase complex.

Zusammenfassung Es wird über thermoanalytische und polarisationsmikroskopische Untersuchungen zur Kristallisationskinetik unterschiedlich präparierter Mischungen aus Polyethylen und Polyoxymethylen (POM) berichtet. Im DSC-Experiment zeigt sich bei extrudiertem Material ein zusätzlicher Kristallisationspeak, der einer verzögert kristallisierenden POM-Fraktion zuzuordnen ist. Es wird gezeigt, daß die Beobachtung auf eine zusätzliche, durch die Phasengrenzfläche induzierte inhomogene Keimbildung und Kristallisation zurückzuführen ist. Dies ist genau dann möglich, wenn in entmischten Systemen die präparativ einstellbare Anzahl der Partikel der dispersen Fraktion die materialbedingte Anzahl der Fremdkeime übersteigt.

The piezo- and pyroelectric coefficients of a number of materials are not constant but depend on the strength of the applied mechanical or thermal load, respectively. The nonlinear contributions are investigated and treated in the present paper by means of the Maxwell relation technique of thermodynamics, this yielding the physics and the strength of the corresponding inverse effects. The considerations reveal that the latter consist in electric field dependences of elastic moduli, of volume compressibility, of thermal expansion, and of specific heat at constant pressure. Equations are presented which relate the various activity coefficients. The strengths of the respective effects are estimated for poly (vinylidene fluoride) which exhibits a rather strong nonlinear piezo- and pyroelectricity. They are, however, beyond the resolution power of the usual experimental arrangements.

Some of the piezoelectric constants of poly(vinylidene fluoride), PVDF, are distinctly stress dependent. The description of time dependent piezoelectric effects in this material, therefore, requires consideration of response terms of at least second order in the exciting stress. In the present paper, generally valid dispersion relations for a linear and second order response are calculated on the basis of suitable equations of second order response theory. These are then used to evaluate the piezoelectric effect in PVDF. The second order static piezoelectric constant of this material turns out to be -7.7 × 10-20Cm2/N2.

Composition profiles develop around growing PVDF spherulites in a blend with PMMA. These profiles assume stationary courses after a certain crystallization time provided that the overall degree of crystallinity is not too high. The composition-dependent growth rate and the diffusion-controlled remove of the surplus PMMA from the spherulite surface are then in a stationary equilibrium. The internal structure of the spherulites will then be homogeneous, too. Upon isothermal crystallization of a PVDF/PMMA = 60/40 (wt %) blend at 160°C for at least 4 h, the spherulites internal degree of crystallinity xc as related to the PVDF fraction obeys the inequality 55 wt % ≤ xc ≤ 84 wt %. The overall PMMA content within the spherulites as averaged over its whole inside has been determined by IR microscopy. It amounts to about 15 wt %. In contrast, the PMMA content of the amorphous phase within the spherulites (averaged again over its whole inside) ranges between 28 and 52 wt %. This composition jumps at the spherulite surface to 52 wt %. From the slope of the composition profiles outside the spherulites that have a width of more than 50 μm, the effective chain diffusion coefficient in blends as averaged over both components can be calculated to amount to (250 ± 100) μm²h⁻¹. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2923–2930, 1998

The complex permittivities of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperature T(20°-60°C), frequency v(5 Hz-300 kHz), and hydrostatic pressure p (0-260 MPa). The values can be represented by a master curve with the shift factors △p/△ log (v/Hz) = -140 MPa at room temperature and △ (1 /T) /△ log (v/Hz) = -2. 10-4 K-1 at atmospheric pressure. The dependence of the activation energy △EA on pressure p is then given by △EA=(100 + 0.02 MPa-1p) kJ/mol. Furthermore, the results indicate that the β-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group.

Some of the piezoelectric constants of PVDF are strictly stress dependent. This behaviour is assumed to originate in a contribution of the interphase region between crystalline and amorphous phases to the piezoelectric effect in this material. This assumption is supported by the changes in piezoelectricity after irradiation with fast electrons. Such treatment causes crosslinking predominantly in the amorphous regions and, consequently, significant changes in the mobility of molecular electric moments. The piezoelectric constants become smaller upon irradiation, this being caused by a reduced permanent polarization, by increased mechanical stiffness, and by the reduced reorientability of the molecular electric moments in the interphase. One of the nonlinear piezoelectric coefficients changes its sign at a certain irradiation dose.

Ricin A chain is a polypeptide of 267 amino acids containing a hydrophobic region near its carboxyl-terminus (residues 245-256) which has been implicated in the membrane translocation step necessary for this catalytically active toxin to reach its intracellular substrate. DNA fusions were constructed that encoded hybrid proteins consisting of carboxyl-terminal residues 233-267 or residues 238-267 of ricin A chain preceding mouse dihydrofolate reductase. When in vitrotranscripts prepared from these constructs were translated in cell-free systems, the ricin A chain-derived sequences functioned as efficient signal peptides which directed dihydrofolate reductase into microsomes or into proteoliposomes containing microsomal membrane components.

Some of the piezoelectric coefficients of poly (vinylidene fluoride) are distinctly stress dependent. It is reported on their dependence on the frequency of an oscillatory stress and on the magnitude of an superimposed offset stress. In order to explain the observed dynamic and nonlinear piezoelectric properties, a model is developed that attributes them to changes in the local polarization in an interphase between the crystalline and amorphous phases in this semi-crystalline polymer.