共查询到20条相似文献，搜索用时 15 毫秒
1.
Wei Li Binbo Jiang Alina Buda Jingdai Wang Bernhard Blümich Yongrong Yang Jie Zheng 《Journal of Polymer Science.Polymer Physics》2010,48(12):1363-1371
Novel exfoliated polyethylene (PE)/palygorskite nanocomposites prepared by in situ polymerization are characterized by solid‐state nuclear magnetic resonance (NMR). The phase structure and molecular mobility are investigated by a combination of proton and carbon NMR. The results showed that incorporation of small amounts of palygorskite had great influence on the phase structure and molecular mobility. The incorporated palygorskite hindered the crystallization process and introduced motion‐hindered chains in the NMR crystalline and amorphous phase. 13C cross‐polarization and magic‐angle spinning NMR revealed two orthorhombic crystalline phase with different line‐width. The chain mobility of orthorhombic crystalline phase with broad resonance line is obviously hindered compared with the phase with narrow resonance line when the filler is introduced. Additionally, the results of pulsed field gradient NMR technique show those the tortuosities in the nanocomposites are much higher than that in the bulk PE. The self‐diffusion process of probe molecules is also influenced by the palygorksite load. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1363–1371, 2010 相似文献
2.
Liying Wang Pengfei Fang Chaohui Ye Jiwen Feng 《Journal of Polymer Science.Polymer Physics》2006,44(19):2864-2879
Solid‐state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene‐co‐vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room‐temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well‐defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin‐lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt‐like amorphous phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2864–2879, 2006 相似文献
3.
Li‐Bong W. Lee Richard A. Register David M. Dean 《Journal of Polymer Science.Polymer Physics》2005,43(1):97-106
Blown films of ethylene/methacrylic acid copolymers and ionomers can exhibit pronounced directional tear, meaning that a tear can propagate with much less resistance in a particular direction. However, films blown from the same resin can exhibit different preferred tear directions, which depend on the process conditions. Through wide‐ and small‐angle X‐ray scattering, we demonstrate that this directional tear behavior is a direct result of the orientation of the lamellar polyethylene crystallites in these films; tears propagate more readily between lamellae than through lamellae, as previously recognized for low‐density polyethylene homopolymer. Unlike polyethylene homopolymer, however, an increase in the blowup ratio during the film processing of ethylene/methacrylic acid copolymers and ionomers leads to a 90° rotation of the lamellae that form upon subsequent crystallization. The lamellar rotation arises from a change in the orientation of the row nuclei that form after the melt is inflated and produces a consequent rotation of the preferred tear direction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 97–106, 2005 相似文献
4.
M. Y. Gelfer A. Waddon K. Schmidt‐Rohr R. Gale L. Kleiner R. Berggren 《Journal of Polymer Science.Polymer Physics》2001,39(22):2774-2780
The 50% increased permeability after annealing of semicrystalline poly(ethylene/vinylacetate) containing 3 mol % vinylacetate is linked to increased mobility in the amorphous phase, as identified by line‐narrowing of 1H wideline nuclear magnetic resonance (NMR) spectra and by reduced cross‐polarization efficiency in 13C NMR. Other morphological parameters, such as crystallinity, measured as 30 to 35% by differential scanning calorimetry (DSC) and NMR, are hardly changed by annealing. Small‐angle X‐ray scattering and NMR studies, using spin diffusion as well as T1ρ and T1 relaxation, detected only a small increase in crystallite thickness. The annealing‐induced enhancement in segmental mobility in the amorphous regions corresponds to a temperature shift of about 10 K, from which an increase of the motional rate by a factor of 2 is estimated, and which can account for the enhancement in the permeability. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2774–2780, 2001 相似文献
5.
Zhaofu Fei Holger Thnnessen Peter G. Jones Lindsey Crowe Robin K. Harris Reinhard Schmutzler 《无机化学与普通化学杂志》2000,626(8):1763-1772
The reaction of the bis‐chlorophosphines 1 a – 1 d with bis(2‐chloroethyl)amine hydrochloride in the presence of triethylamine and with various trimethylsilylamines led to a new class of bis‐phosphorus ligands 2 a – 2 c and 3 a – 3 g . 31P‐NMR studies suggested that the bis‐phosphorus ligands undergo rotation reactions about the alkyl bridge in polar solvents. Compounds 2 a – 2 c showed initially only one sharp singlet each in their 31P‐NMR spectra. After a few days at room temperature, two signals were observed. Similar results were observed for 3 a – 3 g . In the solid state, the two phosphorus atoms in 2 c are not equivalent, as was confirmed by the observation of two signals in the solid state 31P‐NMR spectrum. Oxidation reactions of 2 a – 2 c by the hydrogen peroxide‐urea 1 : 1 adduct (NH2)2C(:O) · H2O2 led to the formation of the corresponding phosphoryl compounds 4 a – 4 c . Reaction of 2 a and 3 a with Pt[COD]Cl2 (COD = 1.5‐Cyclooctadiene) furnished the complexes 5 and 6 . The NMR spectra suggested that the two chlorine atoms are in cis position. X‐ray structure analyses were conducted for 2 a , which exhibits twofold symmetry; 2 c , which is linked into dimers by hydrogen bonds C–H…O; and 6 , confirming the cis configuration. 相似文献
6.
Clara Strandberg Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2007,45(10):1848-1859
Oxidation of polyethylene (PE) gives a mixture of degradation products. Carboxylic acids are among the major ones. They are believed to cause off‐flavor in food and beverage packaging. Our previous research has shown that identification and use of indicator products gives earlier detection of oxidation in plastic materials. In the present study, the relation between off‐flavor in water extracts of PE and each of the carboxylic acids in the homologous series from propanoic to nonanoic acid were investigated. Also, a comparison between carbonyl index in solid PE and each of the carboxylic acids in the homologous series from propanoic to decanoic acid were examined. The amount of the carboxylic acids was assessed by head‐space solid‐phase microextraction (HS‐SPME) and gas chromatography–mass spectroscopy (GC‐MS). It was found that the amount of butanoic and hexanoic acid correlated well with the rated off‐flavor intensities in the water extracts. This confirmed earlier results on a linkage between these two carboxylic acids and highly rated off‐flavor intensities. Moreover, a relation between the build‐up of propanoic acid in the solid PE and carbonyl index was found. Hence, propanoic acid could be used as an indicator product for earlier oxidation detection in these PE materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1848–1859, 2007 相似文献
7.
Kazuko Suzuki Charlotte Martineau Gerhard Fink Stefan Steuernagel Francis Taulelle 《Magnetic resonance in chemistry : MRC》2012,50(2):159-168
Cross polarization–magic angle spinning (CPMAS) is the most used experiment for solid‐state NMR measurements in the pharmaceutical industry, with the well‐known variant RAMP–CPMAS its dominant implementation. The experimental work presented in this contribution focuses on the entangled effects of the main parameters of such an experiment. The shape of the RAMP–CP pulse has been considered as well as the contact time duration, and a particular attention also has been devoted to the radio‐frequency (RF) field inhomogeneity. 13 C CPMAS NMR spectra have been recorded with a systematic variation of 13 C and 1H constant radiofrequency field pair values and represented as a Hartmann‐Hahn matching two‐dimensional map. Such a map yields a rational overview of the intricate optimal conditions necessary to achieve an efficient CP magnetization transfer. The map also highlights the effects of sweeping the RF by the RAMP–CP pulse on the number of Hartmann–Hahn matches crossed and how RF field inhomogeneity helps in increasing the CP efficiency by using a larger fraction of the sample. In the light of the results, strategies for optimal RAMP–CPMAS measurements are suggested, which lead to a much higher efficiency than constant amplitude CP experiment. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
Annealing treatments have been performed on two melt‐crystallized polyethylenes (PE) with different topologies, namely highly branched and linear PE, to comparatively investigate the microstructural evolution and corresponding changes of mechanical property. It shows that annealing induced different degrees of variation in the lamellar rearrangement of the two PEs. Branched PE, which incorporates comonomers on the backbones, shows a more versatile annealing effect when compared with the linear counterpart. With respect to PEs, it is for the first time a connection was made between the annealing‐induced microstructural changes and an important but less understood property known as heat distortion temperature (HDT). It shows that at lower annealing temperatures, the improvement of HDT can be well correlated to the increased crystallinity induced by lamellar rearrangement for both PEs. However, for branched PE, the contribution of crystallinity is weakened at higher annealing temperatures and the dominant factor on HDT was replaced by the relaxation of lamellar structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1347–1359, 2011 相似文献
9.
Tai‐Yon Cho Eun Ji Shin Wonhee Jeong Barbara Heck Robert Graf Gert Strobl Hans W. Spiess Do Y. Yoon 《Macromolecular rapid communications》2006,27(5):322-327
Summary: A systematic investigation of the microstructure of ethylene copolymers has been carried out as a function of the comonomer type and content, employing small‐angle X‐ray scattering (SAXS) experiments to study the lamellar structure, and solid‐state NMR to study the local conformational freedom. The SAXS results clearly show that the major consequence of incorporating comonomers (butene and octene) is the absence of lamellar thickening during the crystallization. From solid‐state NMR study, applying the rotor‐encoded rotational echo double resonance technique (REREDOR), it is found that the extent of the orientational order in the noncrystalline region of semicrystalline polyethylene is substantial but this order is not significantly affected by the incorporation of comonomer units. Therefore, the major cause for the significant improvements of mechanical properties observed for ethylene copolymers is not a change in the thermodynamic state of the noncrystalline region, but most likely a significant change in the intermolecular topological structure due to the blocking of disentanglement processes required by the lamellar thickening step during crystallization.
10.
Fabiana De C. Fim Tiago Machado Denise Santos De Sá Paolo R. Livotto Zênis N. Da Rocha Nara R. De S. Basso Griselda Barrera Galland 《Journal of polymer science. Part A, Polymer chemistry》2008,46(11):3830-3841
A novel complex dichlorobis(2‐ethyl‐3‐hydroxy‐4‐pyrone)zirconium(IV) (ZrCl2(ethylpyrone)2) was synthesized. Complexation of the pyrone ligand to the zirconium was confirmed by UV, 1H and 13C‐NMR, and electrochemical studies. NMR showed the presence of four isomers and density functional theory calculations indicated that the main isomer had a cis configuration. The catalyst was shown to be active in ethylene polymerization in the presence of the cocatalyst methylaluminoxane. The highest catalyst activity for the zirconium complex was achieved at Al/Zr = 2500, 70 °C and when a small concentration of catalyst was used (1 μmol). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3830–3841, 2008 相似文献
11.
Yury V. Kissin 《Macromolecular theory and simulations》2002,11(1):67-76
The previously developed kinetic scheme for olefin polymerization reactions with heterogeneous Ziegler–Natta catalysts states that the catalysts have several types of active centers which have different activities, different stabilities, produce different types of polymer materials, and respond differently to reaction conditions. In the case of ethylene polymerization reactions, each type of center exhibits an unusual chemical feature: a growing polymer chain containing one ethylene unit, Ti—C2H5, is unusually stable and can decompose with the formation of the Ti—H bond. This paper examines quantitative kinetic ramifications of this chemical mechanism. Modeling of the complex kinetics scheme described in the Scheme demonstrates that it correctly and quantitatively predicts three most significant peculiarities of ethylene polymerization reactions, the high reaction order with respect to the ethylene concentration, reversible poisoning with hydrogen, and activation in the presence of α‐olefins. 相似文献
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14.
Quantitative Structural Constraints for Organic Powders at Natural Isotopic Abundance Using Dynamic Nuclear Polarization Solid‐State NMR Spectroscopy 
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下载免费PDF全文 Dr. Giulia Mollica Myriam Dekhil Dr. Fabio Ziarelli Dr. Pierre Thureau Prof. Stéphane Viel 《Angewandte Chemie (International ed. in English)》2015,54(20):6028-6031
A straightforward method is reported to quantitatively relate structural constraints based on 13C–13C double‐quantum build‐up curves obtained by dynamic nuclear polarization (DNP) solid‐state NMR to the crystal structure of organic powders at natural isotopic abundance. This method relies on the significant gain in NMR sensitivity provided by DNP (approximately 50‐fold, lowering the experimental time from a few years to a few days), and is sensitive to the molecular conformation and crystal packing of the studied powder sample (in this case theophylline). This method allows trial crystal structures to be rapidly and effectively discriminated, and paves the way to three‐dimensional structure elucidation of powders through combination with powder X‐ray diffraction, crystal‐structure prediction, and density functional theory computation of NMR chemical shifts. 相似文献
15.
C. H. Stephens H. Yang M. Islam S. P. Chum S. J. Rowan A. Hiltner E. Baer 《Journal of Polymer Science.Polymer Physics》2003,41(17):2062-2070
A series of chlorine‐containing polymers were prepared by ring‐opening metathesis polymerization (ROMP) followed by hydrogenation. This synthesis route was chosen specifically so that chain microstructures would be obtained that resembled copolymers of ethylene and vinyl chloride. The chlorine content was varied by the copolymerization of 5‐chlorocyclooctene and cyclooctene. Differential scanning calorimetry, light microscopy, tapping‐mode atomic force microscopy, wide‐angle X‐ray diffraction (WAXD), and density were employed to characterize the polymers. The copolymers had certain restrictions on the length of the methylene sequence between substituted carbons, however, ROMP copolymerization introduced enough variation in the methylene sequence length that model copolymers with the equivalent of 14 mol % vinyl chloride or less closely resembled random copolymers of ethylene and vinyl chloride. These materials organized as spherulites and exhibited the orthorhombic crystal form. Constraints on the placement of chlorine atoms strongly affected the crystallization of polymers with more than the equivalent of 14 mol % vinyl chloride. More regular chlorine substitution along the polyethylene chain translated into better ordered crystal structures with sharp melting peaks. The granular morphology of these materials at ambient temperature was interpreted as fringed micellar crystals. The WAXD patterns provided definitive evidence that chains in the fringed micelle took the hexagonal crystal form. The lower density hexagonal form facilitated the crystallization of short ethylene sequences and accommodated chlorine atoms more easily than the orthorhombic form. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2062–2070, 2003 相似文献
16.
Aletta Du Toit Deon De Wet‐Roos Dawie J. Joubert Albert J. Van Reenen 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1488-1501
Ethylene‐styrene (or 4‐methylstyrene) co‐oligomerization using various bis(diphenylphoshino)amine ligands in combination with chromium is discussed. GC analysis of the reaction mixture shows that various phenyl‐hexene and phenyl‐octene isomers are formed either through cotrimerization or cotetramerization. It seems that the more bulky ligands display lower selectivity to co‐oligomerization and favor ethylene homo‐oligomerization. Subsequent copolymerization of the oligomerization reaction mixture using a metallocene polymerization catalyst results in a copolymer with a branched structure as indicated by Crystaf and 13C NMR analysis. Assignments of the 13C NMR spectrum are proposed from an APT NMR experiment combined with calculated NMR chemical shift data using additivity rules. An indication of the ability of the different co‐oligomerization products to copolymerize into the polyethylene chain could be established from these assignments. Unreacted styrene and the more bulky isomers, 3‐phenyl‐1‐hexene and 3‐phenyl‐1‐octene, are not readily incorporated while branches resulting from the other isomers present in the co‐oligomerization reaction mixture are detected in the NMR spectrum. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 1488–1501, 2008 相似文献
17.
Dan Baugh O. David Redwine Angela Taha Ken Reichek Janece Potter 《Macromolecular Symposia》2007,257(1):158-161
Summary: Detection and quantification of long-chain branches in some polyethylene copolymers is challenging due to the near coincidence of the chemical shifts for the carbons at the short-chain and long-chain branches present in these copolymers. The small chemical shift difference can be enhanced by changes in solvent and temperature. This allows one to use lower field magnets for some copolymers. Results are presented comparing several solvents and blends at a variety of temperatures using 500, 600 and 750 MHz spectrometers. 相似文献
18.
Yingying Lu Youliang Hu Z. M. Wang E. Manias T. C. Chung 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3416-3425
This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s‐PS), and elastomers, such as poly(ethylene‐co‐1‐octene) and poly(ethylene‐co‐styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ～270 °C to low glass‐transition temperature ～?60 °C. The chemistry involves two reaction steps, including the preparation of a borane group‐terminated polyolefin by the combination of a metallocene catalyst and a borane chain‐transfer agent as well as the interconversion of a borane terminal group to an anionic (? O?K+) terminal group for the subsequent ring‐opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α‐olefins to the ring‐opening polymerization of ethylene oxide. The well‐defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (Mw/Mn < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002 相似文献
19.
Qiujin Zhang Weixin Lin Guang Yang Qun Chen 《Journal of Polymer Science.Polymer Physics》2002,40(19):2199-2207
The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line 1H NMR and solid‐state high‐resolution 13C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential 13C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer 13C NMR spin–lattice relaxation time (T1) was attributed to the internal part of the crystalline region, whereas the component with shorter 13C NMR T1 to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the 13C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002 相似文献
20.
2H NMR spin relaxation study of the soft segment motion in alternating ethylene–propylene copolymers
《Magnetic resonance in chemistry : MRC》2002,40(2):161-164
We synthesized three partially deuterated polymer samples, namely a poly(ethylene‐alt‐propylene) (EP) alternating copolymer, a poly(styrene‐b‐EP) diblock copolymer (SEP) and a poly(styrene‐b‐EP‐b‐styrene) triblock copolymer (SEPS). The 2H spin–lattice relaxation time, T1, of EP soft segments above their glass transition temperature was measured by solid‐state 2H NMR spectroscopy. It was found that the block copolymers had a fast and a slow T1 component whereas EP copolymer had only a fast component. The fast T1 components for SEP and SEPS are similar to the T1 value of EP above ca 20°C. The slow T1 component for SEP and SEPS exhibited a minimum at 60°C and approached the value of the fast component near the Tg of polystyrene. The motional behavior of the EP units for SEP is similar to that of SEPS over the entire range of temperature. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献