Short-range order in noncrystalline polymers examined with spin-polarized neutrons

The application of spin-polarized neutrons with spin polarization analysis to study diffraction patterns from polymers is discussed. The experimental separation of the coherent and incoherent parts of the scattering coupled with the use of the internal standard resulted in the quantitative analysis of the purely coherent scattering from unfunctionalized and functionalized polystyrene in terms of absolute units. This allowed us to model the scattering curves in terms of paracrystallinity. © 1993 John Wiley & Sons, Inc.     

Dislocations and paracrystallinity in polymers

It is shown, that paracrystallinity in polymers can be explained by assuming a statistical dislocation distribution inside the crystal lattice. This conclusion is based on X-ray scattering results (line width measurements).     

Computer simulation of diffuse X-ray scattering by an aligned smectic C-like nematic phase

We report a new method for the quantitative analysis of diffuse X-ray scattering by some disordered smectic phases. Computer simulations of diffuse X-ray scattering are compared with actual diffraction patterns of a series of oriented liquid crystalline polymers TDI-C _m C _n . The simulation shows that both Bragg peaks (spots) and equidistant streaks (diffuse scatterings) are diffracted by one smectic C-like structure in which each of the molecular chains is displaced from its mean position by a random distance Δ _z , along the chain axis (z). This is a first type of disorder. By assuming a Gaussian distribution of the disordered displacements, the mean value of Δ _z has been determined from the position and intensity of the streaks and Bragg peaks for the polymers.     

The scope of metastable peak observations

This short review focuses attention upon the present status of metastable ion studies with emphasis upon the relationship between metastable peak shapes, ion structur and fragmentation mechanisms. Some recommendations are made concerning nomenclature and the reporting of observations on Gaussian-type metastable peaks. Experimental methods for recording relative abundances of metastable peaks are critically appraised. The relationship between metastable ion phenomena and isomerization of gaseous ions is reviewed with particular attention drawn to the effect of rate-determining isomerizations. The shapes of Gaussian-type metastable peaks are discussed in some detail and selected examples from recent studies are used to show that such peaks may, by appropriate experiments, be separated into two Gaussian-type components thus revealing new features of the fragmentation reaction. The magnitude and significance of released kinetic energies, T, are considered and it is stated that few conclusions can be drawn from the evaluation of T alone; the importance of accurate thermochemical data as an aid to understanding and interpreting kinetic energy release data is emphasized. Other topics discussed include composite metastable peaks, metastable peaks produced in chemical ionization and field ionization and the partitioning of internal energy of the fragmenting ion into translational degrees of freedom of the products, for reactions with and without a reverse energy barrier.     

电子衍射径向分布函数测定稀土顺1,4聚丁二烯的原子间距分布

本文用电子衍射径向分布函数测定了稀土顺1,4聚丁二烯的原子间距分布。从电子衍射实验强度曲线的傅里叶变换得到的RDF曲线上,具有二个分子内峰和三个分子间峰。说明在熔点以上,处于非晶态的顺1,4聚丁二烯中不同程度的存在分子链间的局部有序性。     

Phase transitions in the product of spontaneous polymerization of the acrylamide complex of calcium nitrate

Phase transitions in the spontaneously polymerized acrylamide-calcium nitrate system have been studied by X-ray diffraction analysis. The polymerization occursvia the stage of formation of crystalline particles, which exist in a homogeneous solution and are identical to crystallites in chemical composition. At the stage of particle formation, the degree of crystallinity is 60 %, the particle size is 65 nm, and paracrystallinity is 0.0208. An amorphous metal-containing polymer is the final structural state of the system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1764–1766, September, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4162).     

Polymerization of N-(fluoro phenyl) maleimides

Poly(N-aryl maleimide)s of characteristic structures have been synthesized and some of their physical properties studied. These include N-(2-fluoro phenyl), N-(3-fluoro phenyl), N-(4-fluoro phenyl), N-(2,4-difluoro phenyl), N-(2,5-difluoro phenyl), N-(2,3,5,6-tetrafluoro phenyl), and N-(pentafluoro phenyl). The polymerization of N-(fluoro phenyl) maleimides by free-radical initiation in bulk or in solution and by anionic catalyst have been studied to compare the characteristics of polymerization by γ-ray irradiation with that by free-radical initiation. The polymers were characterized by elemental analysis, intrinsic viscosity, spectroscopy (IR and NMR), programmed thermogravimetric analysis, and x-ray diffraction. Spectra of polymers prepared by radiation and anionic polymerization were nearly identical with those of polymers prepared by free-radical polymerization initiated by AIBN in bulk or in solution and by the self-initiated thermal polymerization. A variety of reaction conditions were tried, but all attempts to change the molecular structure of the polymers were unsuccessful. Rates of thermal degradation for poly[N-(fluoro phenyl) maleimide]s have been analyzed by using a multiple-heating-rate procedure. Overall activation energy, order of reaction, and frequency factor have been evaluated. On the basis of the comparison between the overall activation energy of the thermal degradation of poly[N-(fluoro phenyl) maleimide]s and NMR spectra of their corresponding monomers, it can be concluded that the ¹H shifts due to ethylenic protons are so characteristic in sign and magnitude as to be useful in thermal stability elucidation. Some qualitative explanations were given on the stability of these polymers as affected by the type and size of the substituent. The x-ray diffractograms of all samples show two rather broad peaks indicative of noncrystalline structures. The location of the peaks does not depend upon preparation conditions and temperature. Poly(N-maleimide)s of fluoroanilines have not been hitherto described.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. V. Effects of p-benzoquinone and dose rate on methyl methacrylate–silica gel system

In order to elucidate the mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the effects of p-benzoquinone addition and dose rate were studied in detail. Most of the polymerization is inhibited by p-benzoquinone at levels above 10^-2 mole/l. The GPC spectra of both graft polymers and homopolymers show two peaks. The high molecular weight material appears to have been formed by polymerization by a radical mechanism, because these peaks decrease as p-benzoquinone concentration increases; on the other hand, their low molecular weight polymers seem to be products of an ionic polymerization mechanism because those peaks are almost not affected by p-benzoquinone. The four GPC peaks differ in dose rate dependences of their polymerization rate. The dose-rate exponents of polymerization rate were obtained for the four GPC peaks. The behavior of the low molecular weight peaks of graft polymers and homopolymers were quite different, suggesting that the polymers differ considerably in formation mechanism.     

Vergleichende Untersuchung von Reaktivitäten und Ionenstrukturen beim monomolekularen Abbau isomerer Hydroxyzimtsäuremethylester unter Elektronenbeschuss

Comparative investigation of reactivities and ion structures upon electron impact induced degradations of the isomeric hydroxy cinnamic acid methyl esters By analysis of energy release data in metastable peaks it is shown that m- and p-hydroxy cinnamic acid methylesters retain specific structural features upon degradation under electron impact, although their spectra are very similar and the shapes of the metastable peaks due to the initial methoxy cleavage are identical. A pronounced charge radical localization in the molecular ion is indicated. The o-isomer is found to yield a coumarin type structure by elimination of methanol, whose further degradation by decarbonylation involves at least three different mechanisms. The resulting ion structures are different from benzofuran.     

Dielectric studies of tetraaryl and triaryl polycarbonates and comparisons with bisphenol A‐polycarbonate

The relative permittivity, loss, and breakdown strength are reported for a commercial sample of bisphenol A‐polycarbonate (comm‐BPA‐PC) and a purified sample of the same polymer (rp‐BPA‐PC) as well as for two new polycarbonates having low molecular cross‐sectional areas, namely a copolymer of tetraaryl polycarbonate and BPA‐PC (TABPA‐BPA‐PC) and a triaryl polycarbonate homopolymer (TriBPA‐PC). The glass transition temperatures of the new polymers are higher than the T_g of BPA‐PC (187 and 191 °C vs. 148 °C). Relative permittivity and loss measurements were carried out from 10 to 10⁵ Hz over a wide temperature range, and results for the α‐ and γ‐relaxation regions are discussed in detail. For the α‐relaxation, the isochronal peak position, T_α, scales approximately with T_g. On the other hand, the peak temperature for the γ‐relaxation is approximately constant, independent of T_g. Also, in contrast to what is observed for α, γ exhibits a strong increase in peak height as temperature/frequency increases and a significant difference is found between Arrhenius plots determined from isochronal and isothermal data analyses. Next, the γ‐relaxation region for comm‐BPA‐PC and associated activation parameters show strong history/purity effects. The activation parameters also depend on the method of data analysis. The results shed light on discrepancies that exist in the literature for BPA‐PC. The shapes of the γ loss peaks and hence glassy‐state motions for all the polymers are very similar. However, the intensities of the TriBPA‐PC and TABPA‐BPA‐PC γ peaks are reduced by an amount that closely matches the reduced volume fraction of carbonate units in the two new polymers. Finally, for comm‐BPA‐PC, the breakdown strength is strongly affected by sample history and this is assumed to be related to volatile components in the material. It is found that the breakdown strengths for TriBPA‐PC and TABPA‐BPA‐PC are relatively close to that for rp‐BPA‐PC with the value for TriBPA‐PC being slightly larger than that for rp‐BPA‐PC or the value usually reported for typical capacitor grade polycarbonate. Finally, it is shown that the real part of the relative permittivity remains relatively constant from low temperatures to T_g. Consequently, based on the dielectric properties, TriBPA‐PC and TABPA‐BPA‐PC should be usable in capacitors to at least 50 °C higher than BPA‐PC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

RADIAL DISTRIBUTION FUNCTION OF cis-1,4-POLYBUTADIENE BY ELECTRON DIFFRACTION

The interatomic distance function of rareearth catalyzed cis-1,4-polybutadiene was studied by" radial distribution function (RDF) derived from electron diffraction. Two intramolecular peaks and three interrnolecular peaks have been found on the RDF. The appearance of such a number of intermolecular maxima on the RDF can be explained by the local parallel packing of long molecular chains of the amorphous polymers.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. III. Effect of p-benzoquinone and ammonia on radiation-induced polymerization of styrene adsorbed on silica gel

In order to elucidate the mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of p-benzoquinone and ammonia was investigated. The high molecular weight GPC peaks of both graft polymers and homopolymers decreased with increasing p-benzoquinone concentration, while the low molecular weight peaks of both graft copolymers and homopolymers decreased with increasing ammonia concentration. The results indicate that the high molecular weight peaks of both graft and homopolymers are formed as a result of a radical mechanism and that the low molecular weight peaks of both types of polymers are formed by a cationic mechanism. In formation of both graft polymers and homopolymers both radical and cationic polymerization take place at the same time.     

On the Tacticity of Polynorbornenes with 5,6‐endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6‐endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and ¹³C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the ¹³C NMR spectra when the substituents are electron‐withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ε_d, was linearly related to the Hammett constant σ. Polynorbornenes with electron‐withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.     

Plasma polymerization of hexafluoroethane

It was found that when hydrogen is mixed in a plasma, hexafluoroethane polymerization is accelerated. ESCA and IR spectroscopy were used to characterize the resulting polymers and to reveal the reaction mechanism. At relatively low hydrogen/hexafluoroethane ratios and radio-frequency powers of 30 and 100 W (13.56 MHz), no hydrogen could be detected in the polymers with IR spectroscopy. However, after the ratio had increased above one, the hydrogen content increased abruptly. Thus, hydrogen might be looked upon as a sort of scavenger for active fluorine species. ESCA deconvolution analysis of the C_1s peaks of the polymers indicated that the polymer structures were uniform throughout the reactor in the hydrogen/hexafluoroethane system at 30 W, even though the distribution of the deposition rate could still be observed. By examining sodium chloride powder exposed to the plasma with IR spectroscopy, it was possible to detect various fluorosilicates, which indicated ablation of the reactor's glass wall by the plasma.     

A novel method for the synthesis of liquid crystalline polymers. Preparation by the interaction of poly(acryloyl chloride) with mesogenic compounds

A new method for the synthesis of thermotropic liquid crystalline polymers, which is comprised of the interaction of reactive polymers with mesogenic compounds, was investigated. This method is illustrated by the interaction of poly(acryloyl chloride) with p-hydroxybenzylidene-p-butylaniline or p-aminobiphenyl on the preparation of poly(p-acryloyloxybenzylidene-p-butylaniline and poly(N-p-biphenylacrylamide)), respectively. These polymers were subjected to characterization studies which included optical microscopy, x-ray diffraction analysis, and differential scanning calorimetry. It was established that both polymers in the melt exhibit smectic mesomorphism.     

The Usefulness of X-ray Diffraction and Thermal Analysis to Study Dietary Supplements Containing Iron

X-ray powder diffraction (XRPD) and thermal analysis (differential scanning calorimetry/derivative of thermogravimetry (DSC/DTG)) are solid-state techniques that can be successfully used to identify and quantify various chemical compounds in polycrystalline mixtures, such as dietary supplements or drugs. In this work, 31 dietary supplements available on the Polish market that contain iron compounds, namely iron gluconate, fumarate, bisglycinate, citrate and pyrophosphate, were evaluated. The aim of the work was to identify iron compounds declared by the manufacturer as food supplements and to try to verify compliance with the manufacturer’s claims. Studies performed by X-ray and thermal analysis confirmed that crystalline iron compounds (iron (II) gluconate, iron (II) fumarate), declared by the manufacturers, were present in the investigated dietary supplements. Iron (II) bisglycinate proved to be semi-crystalline. However, depending on the composition of the formulation, it was possible to identify this compound in the tested supplements. For amorphous iron compounds (iron (III) citrate and iron (III) pyrophosphate), the diffraction pattern does not have characteristic diffraction lines. Food supplements containing crystalline iron compounds have a melting point close to the melting point of pure iron compounds. The presence of excipients was found to affect the shapes and positions of the endothermic peaks significantly. Widening of endothermic peaks and changes in their position were observed, as well as exothermic peaks indicating crystallization of amorphous compounds. Weight loss was determined for all dietary supplements tested. Analysis of the DTG curves showed that the thermal decomposition of most food supplements takes place in several steps. The results obtained by a combination of both simple, relatively fast and reliable XRPD and DSC/DTG methods are helpful in determining phase composition, pharmaceutical abnormalities or by detecting the presence of the correct polymorphic form.     

Fine structure of polyethylene prepared by γ-ray-induced polymerization in various solvents. III. Selective degradation with ozone

Ozone-degradation products of polyethylenes prepared by γ-ray-Induced polymerization in ethyl alcohol, t-butyl alcohol, and 2,2,5-trimethylhexane were analyzed by gel permeation chromatography (GPC). The ozonized polymers show two discrete peaks in the GPC traces, and the ratio of molecular weights corresponding to the peaks is close to 1:2, suggesting that these polymers are composed of folded-chain crystals similar to solution-grown single crystals. The peak profiles, however, are broad and the peaks in the chromatograms shift concertedly toward lower molecular weight in the course of degradation. These findings suggest that the fold surfaces of the polymers are coarse and that there is no unique crystalline core containing a regularly folded layer. The long period estimated from small-angle x-ray measurements increases with increasing polymerization temperature, but scarcely varies with the solvent type. This implies that when crystallization occurs during polymerization, kinetic factors may have no great effect on crystallization.     

THE EFFECTS OF IRRADIATION ON THE THERMAL PROPERTIES OF SEMI-CRYSTALLINE POLYAMIDES

Irradiation crosslinking of semi-crystalline polyamides was performed by high energy electronswith various dosages. It is known that the melting behavior of the polymers after irradiation is acomplex phenomenon. In company with the wide angle X-ray diffraction and DSC data of irradiatedand unirradiated polyamides it is possible to develop the local order and perfection of the crystallinitiesslightly which resulted from introduction of intermolecular crosslinking in amorphous region, incl-uding in amorphous-crystalline interface and crystalline defect regions due to irradiation. It canbe explained that slight increase of melting temperature (T_m) and heat of fusion (△H_f) with increasingdosage for both of higher crystallinity nylon 4 and nylon 6. For irradiated lower crystallinity nylons,in contrast, the T_m and △H_f decrease obviously with increasing dosage. In this case, radiation cross-linking "freeze in" the pre-existing morphology, and then the prevention for reorganization duringheating is a dominant effect. The T_m from the second melting for all of the samples were depressed,corresponding with Flory theory. Therefore the crosslinks imposed on the molecules restrainedthe molecular mobility, and that not only depresses the crystallinity but also increases the imperfec-tion of crystallites when the radiated polymer melted and then recrystallized. These are also reflectedin the depression of heat and entropy of fusion as well as the appearance of double melting peakson the DSC thermograms.     

Fabrication and Characterization of Conductive Conjugated Polymer‐Coated Antheraea mylitta Silk Fibroin Fibers for Biomedical Applications

Conductive polymers are interesting materials for a number of biological and medical applications requiring electrical stimulation of cells or tissues. Highly conductive polymers (polypyrrole and polyaniline)/Antheraea mylitta silk fibroin coated fibers are fabricated successfully by in situ polymerization without any modification of the native silk fibroin. Coated fibers characterized by scanning electron microscopy confirm the silk fiber surface is covered by conductive polymers. Thermogravimetric analysis reveals preserved thermal stability of silk fiber after coating process. X‐ray diffraction of degummed fiber diffraction peaks at around 2θ = 20.4 and 16.5 confirms the preservation of the β‐sheet structure typical of degummed silk II fibers. This phenomenon implies that both polypyrrole and polyaniline chains form interactions with peptide linkages in degummed fiber macromolecules, without significantly disrupting protein assembly. Fourier transform infrared spectroscopy of coated fibers indicates hydrogen bonding and electrostatic interactions exist between silk fibroin macromolecules and conductive polymers. Resulting fibers display good conductive properties compared to corresponding conjugated polymers. In vitro analysis (live/dead assay) of the behavior of human immortalized keratinocytes (HaCaTs) on coated fibers demonstrates improved cell‐adhesive properties and viability after polymers coating. Hence, polypyrrole‐ and polyaniline‐coated A. mylitta silk fibers are suitable for application in cell culture and for tissue engineering, where electrical conduction properties are required.

     

Morphology changes in bulk donor–acceptor poly(benzodithiophene‐benzotriazole) after post‐treatment

The bulk order in donor–acceptor poly(benzodithiophene‐benzotriazole) was improved by two different post‐treatment procedures applied to the specimen. Two‐dimensional wide‐angle X‐ray scattering was used to investigate the structural changes after treatment. After post‐treatment the polymer turned into a highly crystalline morphology with well‐resolved and intensive π‐stacking reflections which were absent in the pristine sample. To understand the ordering mechanisms taking place during the two post‐treatment procedures, structural parameters like coherence length and paracrystallinity were extracted from the X‐ray data indicating the impact on crystallite size and cumulative lattice disorder. During temperature annealing the intralayer packing transforms from amorphous to highly ordered. On the other hand, solvent vapor annealing enhances in higher extent the interlayer organization due to interpenetration of solvent molecules between alkyl side chains. These results provide important insights for the morphology optimization of semicrystalline conjugated polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2327–2334.