Star polymers consisting of poly(ε-caprolactone), PCL, attached to third generation dendrimer, hyperbranched and dendron cores have been studied by differential scanning calorimetry and wide-angle X-ray scattering. The degree of polymerisation of the PCL arms of the star polymers ranged from 14 to 81. The crystal unit cell was the same for the star polymers as for their linear PCL analogues. The star polymers showed a lower degree of crystallinity than the linear PCL, suggesting that the dendritic cores imposed restriction on PCL crystallisation. Slow heating of rapidly cooled samples led to crystal rearrangement—a gradual increase in melting point with decreasing heating rate and recrystallisation followed by additional high temperature melting. The tendency for crystal rearrangement was less pronounced in star polymers based on dendrimer or hyperbranched cores, suggesting that the dendritic cores constitute an obstacle to crystal rearrangement. The star polymers showed higher equilibrium melting points than the linear PCL analogues. It is suggested that covalent attachment of the PCL arms to the dendritic core reduced the positional freedom and the entropy of the melt with respect to that of linear PCL.

The crystal structure of Nd(10)W(22)O(81), neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a = 3.8613 (1), b = 35.9431 (1), c = 21.8900 (1) A, V = 3038.05 A(3), Z = 2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO(3)-type fragments consisting of three octahedra, thus forming W(9)O(32) units. These units form 'pillars' along (a). These 'pillars' are joined by pairs of tilted octahedra (W(2)O(11) groups) to form corrugated layers perpendicular to (b). The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd(10)W(22)O(81) can thus be alternatively given as Nd(5)W(11)O(39 + x) (x approximately 1.5), where x represents the interstitial O atoms. Nd(10)W(22)O(81) is a new type of PC structure.

Indexing of a powder diffraction pattern is still a critical point in procedures aiming at solving crystal structures from powder data. New code has been associated to the program TREOR90 in order to define an efficient peak search procedure, to modify the crystallographic decisions coded into TREOR90 to make it more exhaustive, to refine the selected unit cell automatically, and to make the entire procedure user friendly, via a graphical interface. The new program, called N-TREOR, has been integrated into the package EXPO to create a suite of programs able to provide a structural model from the analysis of the experimental pattern. N-TREOR is also available as a stand-alone program.

A sample of Ta2O5, ditantalum pentaoxide, heat-treated in a "toroid"-type high-pressure chamber at P = 8 GPa and T = 1470 K, was studied by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). Two high-pressure modifications of Ta2O5, isostructural with B-Nb2O5 and Z-Nb2O5, were identified from the X-ray powder pattern. Both structures were refined by the Rietveld method from the X-ray diffraction data: B-Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) A, beta = 104.264 (2)degrees, V = 332.45 A3, Z = 4, space group C2/c; Z-Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) A, beta = 108.200 (2)degrees, V = 136.53 A3, Z = 2, space group C2. The Z-Ta2O5 modification is new. The Ta atoms are six-coordinated in B-Ta2O5 and seven-coordinated in Z-Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect-rich B-Ta2O5 crystals, which could be interpreted as an intergrowth between the B-Ta2O5 and Z-Ta2O5 phases.

The [Co(ZXpy)(2)Y-2]-type solid, tetrahedral complexes where X = Cl, Pr and Y = Cl, Br, I have been prepared from solution, and their thermal properties have been described using the simultaneous TG-DTG-DTA and DSC technique. Vibrations in the mid- and far-infrared spectra have been assigned, and an extra A, deformation band was found, reflecting a possible distortion from the C-2v symmetry. From the indexed X-ray powder diffractograms of the title compounds the unit cell parameters were calculated. The electronic properties and steric factors which effect the stability of the complexes are described in detail.

The transformation of H-Nb2O5has been studied by using a “toroid”-type high-pressure chamber at pressures of 5.0 and 8.0 GPa in the temperature region 800–1400°C. A mixture of B-Nb2O5and a new modification of niobium pentoxide (denoted Z-Nb2O5) with seven-coordinated niobium was found in the samples after treatment atP=8.0 GPa,T=800–1100°C for 1–10 min. The structure was determined and refined by the Rietveld method from X-ray powder diffraction data. The thermogravimetric analysis showed no reduction of the sample.

The influence of film blowing and melt extrusion under different processing conditions on the mechanical properties and molecular weight of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have been characterized. Natural polymers are generally more sensitive to the high temperatures used in processing than synthetic ones. Size exclusion chromatography (SEC) showed that the weight average molecular weight M̄w decreased with increasing processing temperature and decreasing screw speed. A 50% difference in M̄w could be achieved. The modulus of elasticity (E) exhibited only minor changes with processing conditions and was, consequently, not affected by the M̄w. The elongation at yield (ϵy) and break (ϵb) decreased significantly with increasing processing temperature with a maximum at a screw speed of approximately 25 rpm. The stress at yield (σy) decreased with increasing processing temperature. The stress at break (σb) showed a larger variation with processing conditions with values between 21 and 31 MPa. The blown film exhibited values of M̄w, and σb, comparable with those of the extruded samples. The film showed no yield before break and was rather brittle. Both ϵy and ϵb of the extruded samples decreased approximately linearly with decreasing M̄w, and a breaking point in the tensile strength was evident at a value of about 150 000 g/mol below which the mechanical properties decreased rapidly. In addition, σy and σb decreased with decreasing M̄w. The mechanical properties are optimized at a processing temperature of 160–165 °C and a screw speed at about 25 rpm, although it is suggested that these conditions are not optimal if the desire is to achieve rapid embrittlement and disintegration of the polymer.

Crystallinity, crystal structure and lamellar thickness in melt-crystallized samples of poly(propylene-stat-ethylene) fractions with 2.7-11.0 mol% ethylene comonomer and of approximately constant tacticity were assessed by wide- and small-angle X-ray scattering, differential scanning calorimetry and infra-red spectroscopy. Most of the samples were crystallized under isothermal conditions at 373 K. In comparison with an isotactic homopolymer of polypropylene, the copolymers showed lower crystallinity, melting enthalpy and average length of 3/1 helices, a slightly larger unit cell, a longer long period and an invariant lamellar thickness. The X-ray crystallinity of the copolymers remained approximately constant with increasing ethylene content, whereas the gamma-crystallinity increased and the heat of fusion decreased moderately. It is suggested that the ethylene units are partially included in the crystals, and that this causes the invariance in crystallinity and crystal thickness. The observed gradual decrease in average 3/1 helix length with increasing ethylene content as assessed by infra-red spectroscopy is in accordance with this suggestion. Copyright (C) 1996 Elsevier Science Ltd.

The crystallization and melting behaviour and the morphology of fractions of poly(propylene-stat-ethylene) with 2.7–11.0 mol% ethylene were studied by differential scanning calorimetry, wide-angle X-ray scattering, polarized light microscopy and transmission electron microscopy, after etching with permanganic acid. The inclusion of ethylene co-repeating units in isotactic polypropylene (0–11.0 mol% ethylene) caused approximately linear decreases in kinetic and equilibrium melting temperatures and in the glass transition temperature with increasing ethylene content. X-ray scattering showed that the content of the γ form increased with increasing ethylene content, increasing crystallization temperature and decreasing cooling rate from the molten state. It was shown for one of the copolymers (8.7 mol% ethylene) that during heating approximately 50% of the γ form was converted to the α form before the final melting of the sample. The rest of the γ crystals melted without transformation to the α form. The multimodality of the crystal melting above the crystallization temperature in the polymers with a more uniform crystal structure was caused by recrystallization during heating, whereas polymers with appreciable contents of both α and γ forms exhibited multimodal melting at all the heating rates adopted. The size of the low temperature melting peak as assessed at a heating rate of 40 K min−1 was approximately proportional to the initial content of the γ form. By comparison with the spherulitic structure of homopolymers, that of the copolymers was coarser with internal and peripheral pockets of molten material during spherulite growth. The crystal lamellae exhibited more curvature in the copolymer samples than in the homopolymer.

The crystal structure of BaMo3O10 has been determined from X-ray and neutron powder diffraction data using no prior structural information. Direct methods and combined X-ray and neutron Rietveld refinements were used to solve the structure. There are two Ba, six Mo and twenty O atoms in the asymmetric unit. The crystal symmetry is monoclinic (space group P2(1); Z = 4), and the unit cell parameters are a = 14.695(2) Angstrom, b = 7.5704(7) Angstrom, c = 6.9618(6) Angstrom, and beta = 100.381(8)degrees. In a combined Rietveld refinement with 124 variables, the R-F-values 0.034 and 0.046 were obtained for neutron time-of-flight and X-ray data respectively, although small oscillations in some parameters could not be avoided in the final refinement cycles. The structure is built of layers of [Mo3O102-] linked to each other with barium ions. The Mo-O framework contains distorted MoO6 octahedra interlinked by corner-and edge-sharing.

The structures of two high-pressure tungsten oxides, previously studied by high-resolution electron microscopy, were confirmed by Rietveld refinement based on X-ray powder diffraction data. The phases have identical stoichiometry, W3O8, and extremely narrow 00l reflections in common. The microstructure of the dominant phase was investigated by means of X-ray powder diffraction pattern decomposition. A Williamson–Hall plot revealed that all lines, except the 00l reflections, were broadened solely due to the crystallite size effect. A cylindrical model is used to describe the average form of the coherently diffracting domains. The height of the cylinder, whose axis is colinear with the crystallographic c parameter of both phases, is considered “infinite,” and the average diameter of the cylinder model is 655(22) Å. A quantitative confirmation is obtained from electron microscopy.

The temperature dependence of the Zn2+/Mg2+ cation ordering among five- and six-coordinated metal sites in gamma-(Zn1-xMgx)(3)(PO4)(2) solid solutions has been studied by X-ray powder diffraction methods. The structures of polycrystalline samples (P2(1)/n; Z = 2) prepared at and quenched from different temperatures have been refined with the Rietveld technique. The structure factor R-values are in the range 0.04-0.05. It is shown that ordering with zinc preferably at the five-coordinated site is enhanced with temperature. Approximate thermodynamic data for the exchange reaction have been derived.

The correlation between structure and thermal properties of halogeno methylpyridine cobalt(II) is described. The ternary mixed tetrakis-derivatives and the tetrahedral bis-complexes of cobalt(II) chlorides and bromides formed with picolines are structurally very similar to the cadmium(II) and nickel(II) analogues, the iodides are somewhat different, however. On the basis of the characteristic correlation between the densities calculated from powder diffraction data and the molecular weights, the densities of a few thermal intermediates, which have not yet been prepared, are predicted. The square bipyramidal structure of dibromotetrakis(3-methylpyridine)cobalt(II) is described, and the deformation of the octahedra is discussed in detail. Structural study was extended by molecular mechanics (MM+ and MMX) and molecular orbital (SINDO1) calculations.

The microstructure and the thermal and mechanical properties of injection molded samples of different blends of Vectra (LCP) and poly(butylene terephthalate) (PBT) have been studied. Differential scanning calorimetry and hot-stage polarized light microscopy showed that the crystallization of PBT was unaffected by the presence of LCP. X-ray diffraction showed that the PBT component was always unoriented in the injection molded samples. Blends with less than 28 vol% LCP exhibited the same stiffness and the same coefficient of linear thermal expansion as PBT. Blends containing more than 38 vol% LCP contained an oriented LCP phase and had a stiffness in accordance with the upper-bound composite equation. The coefficients of linear ther-mal expansion for these blends were close to that of pure LCP.

Ternary mixed 54-, 2,6-, 3,4- and 3,5-dimethylpyridine complexes of cobalt(II) with chloride bromide and iodide have been prepared and analysed by X-ray powder diffraction techniques. The symmetry and cell dimensions have been calculated by means of TREOR 90, a trial-and-error indexing program.