Wide-angle X-ray Diffraction Studies Research Articles

Conformation and packing of poly(alkylene phosphate) chains in the crystal lattice. Part I: molecular modelling and wide-angle X-ray scattering

Molecular modelling of the poly(alkylene phosphates) suggests a structure in which the repeat distances appear to be in agreement with those indicated by wide angle X-ray diffraction studies of the semi-crystalline polymer. The extended zig-zag chains lie in a parallel array in stacks of pleated sheets. There are lines of phosphoryl groups, linked by hydrogen bonding, running in one direction through the structure which appear to be suitable for the selective transport of ions.

Morphology and elastomeric properties of isotactic polypropylene/ hydrogenated poly(styrene- co-butadiene) blends: a potential for a new thermoplastic elastomer

A single-phase melt of the isotactic polypropylene (iPP)/hydrogenated poly(styrene-co-butadiene) (hSBR) blend, which has a virtual upper critical solution temperature (UCST)-type phase boundary below the melting point of iPP (T.), was prepared at 50/50 wt. ratio and quenched below UCST. By transmission electron microscopy and dynamic mechanical analysis, the blend was shown to be a phase-separated material in which hSBR-rich domains with uniform diameter of ca. 20 rim are dispersed in an iPP-rich matrix. The regular structure is believed to be formed by spinodal decomposition which is pinned at an early stage by crystallization in the iPP-rich region. The blend showed good strain recovery after large deformation, suggesting a potential for a new class of thermoplastic elastomer. Wide-angle X-ray diffraction (WAXD) studies showed that iPP crystallites in the blend are smaller than those in neat iPP and there exists an optimum size of ca. 10 nm (crystal size by the Scherrer equation) for this strain recovery. Such crystallites suffered from less plastic deformation and were hardly oriented under bulk deformation. That is, the crystallites that developed in the presence of polymer impurity (hSBR) seem to be different from those in neat iPP, and play the role of tie points to provide the elastomeric character of the matrix itself.

Cellulosic blends with poly(acrylonitrile): characterization of hydrogen bonds using regioselectively methylated cellulose derivatives

Hydrogen bonds in cellulosic blends with poly(acrylonitrile) (PAN) were characterized in terms of hydroxyl regiochemistry in the cellulosics using Fourier transform infra-red ( FTi.r.) spectroscopy. Regioselectively substituted O-methylcelluloses (MC), 2,3-di- O-methylcellulose (23MC) and 6- O-methylcellulose (6MC), were used as cellulosic model components. Wide-angle X-ray diffraction studies of the cast films of blends having more than 50 wt% cellulosic content showed them to be highly amorphous, indicating the presence of a certain interaction between the cellulosics and PAN. FTi.r. analysis revealed that the hydrogen bonds in cast films washed with solvents were only engaged between the primary hydroxyl groups (OH) at the C-6 position of cellulose and the nitrile group (CN) of the PAN molecule, while there was no evidence for polymer–polymer interactions in the secondary hydroxyl groups at the C-2 and C-3 positions in cellulosics or in the ether oxygens such as ring oxygen (O-5) and glucosidic linkage oxygen. In contrast, the remaining DMAc after film cast seems to have an additional interaction to connect the two polymer components, which makes the blends more miscible. Quantitative analysis was also carried out to ascertain the amounts of OH at the C-6 position engaged in the intermolecular hydrogen bonds.

Synthesis and properties of poly(amide‐imide‐urethane) thermoplastic elastomers

A new class of poly(amide-imide-urethane) thermoplastic elastomers based on two-step synthesis of 4,4′-methylene bis(4-phenylisocyanate) with different polyols (PPG and PTMG) and trimellitic anhydride was synthesized. Both resulting polymers showed semicrystalline structures and were readily soluble in polar solvents such as N-methyl-2-pyrrolidone and dimethyl formamide. The soluble poly(amide-imide-urethane)s afforded transparent, flexible, and tough films. Both new copolymers were then characterized by FTIR spectroscopy, universal tensile tester, simultaneous DTA/TGA (SDT), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction studies, to determine their morphological structures, thermal stability, and mechanical properties. Compared to typical polyurethanes, these polymers exhibited better thermal stabilities due to the presence of imide groups. DSC and X-ray diffraction studies showed semicrystalline patterns for these polymers. Stress–strain properties revealed that these polymers have good extensibility like typical polyurethanes. © 1998 SCI.

Physical characterization of a polyolefinic thermoplastic elastomer

Physical characterization of a commercial polyolefinic thermoplastic elastomer (TPE), Santoprene®, was undertaken to understand the elastomeric nature of the two-phase material in which rubber particles are dispersed in a matrix of polypropylene (PP). Dynamic mechanical analysis showed that the PP matrix contains a small amount of rubber. PP crystal lamellae in rubber particles in a well-annealed sample were observed by transmission electron microscopy, suggesting that PP had been occluded in the rubber phase. Such partial phase-mixing may be caused by homogenization under high shear during dynamic vulcanization. Wide angle X-ray diffraction (WAXD) studies showed that PP crystallites in TPE are smaller than those in neat PP. That is, the occluded rubber in the PP matrix may play the role of impurity to render the smaller crystallites. By WAXD analysis on crystal orientation and its relaxation in stretching and releasing processes, it was shown that the smaller crystallites suffer less plastic deformation and, rather, play the role of tie points to provide the elastic properties of the PP matrix itself. About 40 wt% of process oil was found to be loaded on TPE; however, the oil seems to play a minor role in providing the elastomeric character.

Wide-Angle X-ray Diffraction Study of the Phase Behavior of Vinyl Alcohol−Ethylene Copolymers

The influence of the composition and thermal history on the type of lattice developed has been studied by wide-angle X-ray diffraction measurements in three vinyl alcohol−ethylene, VAE, copolymers with different compositions, which were crystallized from the melt at various cooling rates. The results are compared with those of the corresponding homopolymers, poly(vinyl alcohol) and low-density polyethylene. Both the composition and the cooling rate have been found to determine the crystalline structure of these VAE copolymers. Thus, for the samples slowly crystallized from the melt, a monoclinic lattice is obtained for copolymers VAE71 and VAE68 (with compositions of 71 and 68 mol % VA, respectively) while an orthorhombic lattice has been found for copolymer VAE56 (56 mol % VA). The effect of the cooling rate is very important, since copolymers VAE71 and VAE68 lead to the orthorhombic form when the samples are quenched from the melt. Copolymer VAE56 has been found to crystallize in an orthorhombic lattice...

Synthesis of polyurethane from cashew nut shell liquid (CNSL), a renewable resource

A novel thermoplastic polyurethane was prepared from cardanol, a renewable resource and a waste of the cashew industry. Cardanol was recovered from cashew nut shell liquid (CNSL) by double vacuum distillation. It was characterized by CHN analysis and IR, 1H-NMR, and 13C-NMR spectroscopy techniques. Cardanol is a meta-substituted long chain phenol. The long aliphatic chain unit substituent was found to be a monoene. The monomer, 4-[(4-hydroxy-2-pentadecenylphenyl)diazenyl]phenol was prepared from cardanol. It was a dihydroxy compound as characterized by CHN analyzer, UV, and 1H-NMR spectroscopy. The polyurethane was synthesized from this dihydroxy compound by the treatment with 4,4′-diphenylmethane diisocyanate (MDI) in dimethylformamide (DMF) solvent at 80–90°C under nitrogen atmosphere. The polymer was characterized by 1H-NMR, FTIR, and UV spectroscopy. The elemental analysis was done for determining the percentage content of C, H, and N, and the intrinsic viscosity [η] of polymer showed 1.85 dL/gm. Thermogravimetric investigations (TGA) of the cardanol, the dihydroxy compound, and the polyurethane were performed to study their decomposition. The semicrystalline nature of the PU was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analyzer (DMTA). The wide-angle X-ray diffraction (WAXS) study of PU shew a broad amorphous halo indicative of absence of crystallinity in the polymer, which has been explained as due to strong hydrogen bonding in the hard phase. PU may possibly be useful as a telecommunication and as a nonlinear optical material. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 391–400, 1998

Highly crystallizable poly(ethylene terephthalate) prepared by freeze-extracting solutions

Poly(ethylene terephthalate) (PET) solutions in phenol were crystallized together by dropping the solution into ice water. The solvent was subsequently extracted at a temperature below its melting point with ethanol. Wide-angle X-ray diffraction study indicates that the freeze-extracted PET powder exhibits a much higher crystallizability than a solution cast PET film. The crystallization speed and the ultimate crystallinity for the freeze-extracted PET depend on the concentration of the solution from which the sample was prepared. There is a concentration boundary in the dilute region for crystallizability of PET: near the boundary concentration, the chain coils contain a considerable amount of segments with few chain entanglements.

Cryo-electron diffraction as a tool to study local variations in the lipid organization of human stratum corneum.

The human skin provides the body with a barrier against transepidermal water loss and the penetration of harmful agents (e.g. microbes) from outside. This barrier function is produced mainly by the outermost, nonviable layer of the epidermis, the stratum corneum (s.c.). The s.c. consists of terminally differentiated corneocytes surrounded by a continuous intercellular lipid domain, which contains mostly ceramides, cholesterol and free fatty acids. Small- and wide-angle X-ray diffraction studies have elucidated the lamellar and lateral lipid organizations in these domains. However, these techniques require bulk quantities of SC, as a result of which local structure information on the lipids cannot be obtained. Insights to these local lipid arrangements are important when new transdermal drug delivery systems have to be developed. Therefore, the technique of electron diffraction arose as a tool to study the lateral packing of the lipids in the intercellular domains of SC, locally. In a previous study, the suitability of electron diffraction was demonstrated using a lipid model system that resembled the lipid composition of the SC. The spacings calculated from the electron diffraction patterns were in good agreement with the spacings revealed by wide-angle X-ray diffraction. The results presented here succeed this previous study. We improved the microscope settings and developed a new preparation method to study ex vivo human s.c. by cryo-electron diffraction. The method is based on the conventional tape-stripping method and offers the possibility to study depth-related changes in the lipid organization of human SC. Diffraction patterns of both hexagonal and orthorhombic lipid lattices have been recorded with spacings that resembled those found in human s.c. by wide-angle X-ray diffraction. After lipid extraction, such diffraction patterns could no longer be detected in the samples.

Aggregation structure and fatigue characteristics of (nylon 6/clay) hybrid

A nylon 6/montmorillonite clay hybrid (NCH) with montmorillonite of 2 wt% was prepared. Transmission electron microscopy (TEM) of NCH revealed that the silicate layers of montmorillonite were molecularly dispersed in nylon 6 matrix. Wide angle X-ray diffraction (WAXD) study revealed that crystallites formed in both NCH and nylon 6 were the y-form, and the crystallite size in NCH was larger than that in nylon 6. The temperature dependence of dynamic viscoelasticity of NCH revealed that the magnitude of αa-absorption of amorphous phase of nylon 6 in NCH was smaller than nylon 6, suggesting the restriction of thermal molecular motion in NCH due to the strong ionic interaction between nylon 6 and silicate layers. The fatigue lifetime for NCH was longer than that for nylon 6 and nylon 6 reinforced with surface-modified short glass-fiber(SMSGF/N6) under the identical fatigue conditions, even though they showed almost the same moduli. Fatigue fracture criterion based on energy loss dissipated for irreversible structural change was investigated for NCH, and it was revealed that the total viscoelastic energy loss dissipated for irreversible structural change up to fatigue failure of NCH was larger than that for nylon 6 and (SMSGF/N6). This indicates that the fatigue strength of NCH is superior to that of nylon 6 and (SMSGF/N6).

Some observations on the high-resolution solid-state CP-MAS 13C-NMR spectra of periodate-oxidised cellulose

Oxidation of cellulose by sodium metaperiodate leads to a decrease in the crystallinity. A wide-angle X-ray diffraction (WAXRD) study of oxidised celluloses [2,3-dialdehyde celluloses (DAC), 2,3-dicarboxycelluloses (DCC) and sodium 2,3-dicarboxylate celluloses (NaDCC)] showed that the crystalline peak at 2Θ = 22.7 ° decreased almost proportionately with the degree of oxidation of the starting cellulose. In the WAXRD spectra, no new crystalline peaks were observed for the oxidised celluloses, further indicating their amorphous nature. High-resolution, solid-state, cross-polarisation-magic angle spinning (CP-MAS) 13C nuclear magnetic resonance (NMR) spectra of these same oxidised cellulose samples were recorded in order to investigate the changes occurring with increasing oxidation levels. For each series of spectra of increasing oxidation levels of DAC, DCC and NaDCC an increasing trend towards the formation of a multiplicity of peaks was observed, owing to the numerous stereochemical configurations and rotameric conformations possible. The 98% oxidised cellulose samples represent almost pure compounds (new, linear, cellulose-derived polymers). The spectra and observed chemical shifts for this series are being reported for the first time in this paper. It is shown that solid-state NMR can be useful in investigations of oxidatively degraded celluloses.

Hot-stage wide-angle X-ray diffraction studies of the morphology of a polyurethane ionomer

A polyurethane ionomer with a specific ionic structure was synthesized in an attempt to induce ionic aggregate dissociation at elevated, but observable temperatures. By means of hot-stage wide-angle x-ray diffraction (WAXD), the dissociation could be clearly detected before the onset of degradation.

Moisture sorption mechanism of aromatic polyamide fibers. V: Growth of crystallites in as-spun wet poly(p-phenylene terephthalamide) fiber during dehydration

Wide-angle x-ray diffraction studies were performed for as-spun wet poly(p -phenylene terephthalamide) fiber. The effects of sorbed water on the equatorial diffractions from the (110) and (200) crystal planes and on the meridional diffractions from the (002),(004), and (006) crystal planes were analyzed during desorption and absorption. There was no significant change in the d-spacing from the respective crystal plane irrespective of the moisture (water) regain. The ratio of the diffracted intensity from the (110) diffraction to that from the ( 200 ) diffraction remarkably increased by removing the sorbed water. The crystallite size estimated from the (110) diffraction, L 110 , also increased as the moisture regain decreased, while the L 200 did not increase. The longitudinal size of paracrystallite, D 001 , also remarkably increased with the decrease in moisture regain with the lattice distortion factor, g II , kept unchanged. These results strongly suggested the growth of the crystallite via hydrogen bonds in the lateral (b-axis) direction. The growth of the lateral size of crystallite also accompanied the longitudinal growth of crystallite during desorption.

Rapid Crystallization of Polycarbonate by Shock-Cooling and Freeze-Drying Method

Rapid crystallization of a polycarbonate has been achieved by shock-cooling its very dilute benzene solution and then by sublimationof the solvent under vacuum. The degree of crystallinity of this treated polycarbonate is 42.5% or 46.4% by differential scanning calorimetry (DSC) or wide-angle X-ray diffraction (WAXD) studies respectively. These values are significantly higher than that of the sample prepared by hot precipitation technique.

Direct Observations of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Homopolyester by Scanning Tunneling Microscopy

The structure of a main-chain thermotropic liquid-crystalline homopolyester, poly [(phenylsulfonyl)- p-phenylene 1,10-decamethylene-bis(4-oxybenzoate)] (PSHQ10), having a melting point of approximately 110°C and the nematic-isotropic transition temperature of approximately 175°C, was investigated using scanning tunneling microscopy (STM). For taking STM images we employed two samples of PSHQ10: sample A was an as-cast film which received no thermal treatment and sample B was an as-cast film which was thermally treated above the melting point. The STM images show that (i) sample A has a molecular arrangement which is in good agreement with the crystallographic data obtained in a wide-angle X-ray diffraction study, and (ii) sample B has both crystal-like and bundle regions. The STM images of sample B are interpreted as representing a structure which, according to results obtained by Han et al. [Macromolecules 26 (1993) 3176], is a high-temperature melting crystal formed via recrystallization during annealing.

Synthesis and characterization of poly(N-acyl orN-aroyl ethylenimines) containing various pendant functional groups. II. Copolymers with pendant hydroxyl groups

Poly(N-acylethylenimines) with hydroxyl groups randomly attached to the end of the side chains were synthesized from decenyl/heptyl oxazoline random copolymers. The terminal olefin groups in the polymer side chains react quantitatively with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF solvent. The hydroborated polymers can be oxidized and transformed to the polymers with (SINGLE BOND)OH in their side chains. The polymer backbone is very stable in the hydroboration and oxidation reaction environment. The polymers were named as DH-OH or DM(m/n)-OH, where m and n represent the calculated numbers of monomers with and without the (SINGLE BOND)OH group, respectively. The DH(m/n)-OH copolymers were studied by DSC, wide-angle x-ray diffraction, contact angle measurement, and FT–IR. They are crystalline and show birefringence. In polymers with high concentration of hydroxyl groups, the (SINGLE BOND)OH groups promote polymer crystallization due to their strong interactions. They have very high ΔH of fusion, sharp crystallization peaks, and small supercoolings. Wide-angle x-ray diffraction study of these polymers demonstrated that their alkyl side chains are not fully extended in crystalline domain as those in the DH copolymers. Data from advancing water/ethanol mixture contact angle measurement indicates that most of the (SINGLE BOND)OH groups in the copolymers are buried and the polymer surface is mainly composed of methyl or methylene group. FT–IR study in the carbonyl stretching region proves that the (SINGLE BOND)OH groups can bend back and form hydrogen bonding with the carbonyl groups in the polymer backbone. Though the DH–OH polymers show basically a hydrocarbon surface in a normal environment, both receding water contact angle and peel strength measurements demonstrate that the polymer surfaces can reorganize when they are in contact with a polar liquid. The buried (SINGLE BOND)OH groups can be “pulled” out by polar agents such as water or tape adhesive. © 1996 John Wiley & Sons, Inc.

Processing characteristics and structure development in solid-state extrusion of bacterial copolyesters: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The bacterial copolyesters poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have been successfully commercialized by ICI and are currently being distributed worldwide. Because of their bacterial origin, they are completely biodegradable. This has opened up numerous opportunities to develop new environmentally friendly products. The solid-state extrusion of a series of biodegradable copolyesters (P(3HB-3HV)) was performed in our laboratory with the aim of gaining fundamental understanding about their processability below their melting temperatures. The extrudability windows were found to span the temperature range from 135 to 150°C, depending on the composition of the samples under our experimental setup. The solid-state extrudates were found to exhibit an extra melting endotherm about 15–20°C above their normal melting temperature. This high temperature melting peak increasingly became dominant at lower extrusion temperatures. Wide angle X-ray diffraction studies did not indicate any phase change that might be responsible for this increase in the melting point. Contrary to the expectations, the solid-state extruded samples did not show significant chain orientation along the extrusion direction. This might be a result of fracture of the mass in the barrel into smaller pieces and their randomization during the course of their passage through the die. When the extrusion temperature was raised closer to the melting temperature, the quality of the extrudates was improved, and this was reflected in improvement of their mechanical properties. © 1996 John Wiley & Sons, Inc.

Concentration dependence of crystallinity of polycarbonate by shock-cooling and subsequent freeze-drying of its various solutions

Polycarbonate (PC) can be easily crystallized by injecting a very dilute benzene solution of PC directly into liquid nitrogen, and then freeze-drying to remove the solvent. The crystallinities of these prepared samples were characterized by wide-angle X-ray diffraction (WAXD). The results of WAXD studies showed that there is a concentration boundary in very dilute solution for crystallizability of PC: near the boundary concentration, the solution has a lower chain entanglement level, and as a result, crystallizes more quickly and completely than more highly entangled PC. By annealing these fewer-chain-entanglement samples at 190°C for 289 h, crystallinity reaches a maximum value of 79.6%, which is much higher than that of annealing ordinary or other solution-crystallized samples.

Effect of physical and chemical modifications on microcrystalline parameters of silk fibers

Wide-angle X-ray diffraction studies of physically and chemically treated silk fibers like bivoltine mulberry silk and tassar silk were carried out to evaluate their crystal size, lattice distortion, and minimum enthalpy, as these determine the properties of silk fibers. The results are also compared with tenacity measurement. (C) 1996 John Wiley & Sons, Inc.

Correlation of Tensile Properties With Crystallization Parameters of PP in PP/Ag Composites

Crystallization properties of polypropylene (PP) in PP/Ag composites were estimated from differential scanning calorimetry (DSC) and wide-angle x-ray diffraction studies. The effect of Ag powder and its surface modification with a titanate coupling agent on rates of nucleation and growth of crystallization, crystallite size distribution, and crystallinity was determined from crystallization exotherm peaks. Crystallinity and tensile properties such as modulus, yield strength, and breaking elongation decreased with Ag concentration. Linear correlations were obtained with tensile and crystallization parameters in both types of composites.