Magic Angle Spinning-Cross Polarization 13C NMR of crosslinked unsaturated polyester resins

Summary Magic Angle Spinning-Cross Polarization (MAS-CP) ¹³C NMR spectra of four different unsatured resins reticulated with styrene have been measured.Styrene crosslinks may be constituted essentially by dyads or may consist in (styrene) microdomains (n2), depending mainly upon the molar ratio of maleic acid residues in the original unsaturated polyester to styrene.Also in the case of solid unsaturated resins the MAS-CP ¹³CNMR technique promises to allow structural insights only very difficultly obtainable by more classical indirect means.     

Magic Angle Spinning NMR of Macromolecular and Supramolecular Systems

Sideband patterns in single quantum and double quantum magic angle spinning NMR spectra are reviewed. Their use in elucidating non-covalent interactions, such as hydrogen bonds or pi-pi stacking, is demonstrated by studies of supramolecular systems of current interest. Moreover, the effects of local and collective motions are illustrated by examples from supramolecular and macromolecular science.     

Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates

The reaction products formed in a series of fully "equilibrated," roomtemperature-hydrated, fumed colloidal silica plus lime water mixtures were examined using ²⁹Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally distinct calcium silicate hydrate (C-S-H) phases exist in the system CaO–SiO₂–H₂O. The more silica-rich C-S-H (Ca/Si = 0.65 to 1.0) consists predominantly of long chains of silica tetrahedra (Q² middle units) similar to those found in 1.4-nm tobermorite. The studied more lime-rich C-S-H (Ca / Si = 1.1 to 1.3) consists of a mixture of dimer (Q¹) and shorter chains (Q¹ end units and Q² middle units) similar to that reported for synthetic jennite. No monomer units (Q⁰) were detected.     

Characterization of polycyclohexene by high field 13C-NMR spectroscopy

Summary ¹³C NMR spectrum of polycyclohexene is recorded at 50.5 MHz and interpreted in terms of its different stereoisomers. The ratio of threo to erythro forms in the polymer is 21. The spectrum is also sensitive to tacticity of the polymer chain.     

Techniques for the Measurement of Small Anisotropies in Magic Angle Spinning NMR Spectra

Two novel methods for enhancing the effect of small anisotropies on magic angle spinning (MAS) NMR spectra are described. The first method is a simple two-dimensional (2D) spin echo experiment, which generates rotational sidebands at a fraction of the spinning frequency in the ω₁ dimension, while maintaining the effective spinning speed in ω₂. It is shown that the rotational sidebands in the 2D spectrum are much larger than in a normal one-dimensional MAS spectrum obtained at the same spinning speed, and the relative intensities of the two-dimensional sideband array can be analyzed to yield the anisotropy and asymmetry parameter of the coupling tensor. The second method is designed to measure homonuclear dipolar couplings. We show that the effect of a dipolar coupling between members of an isolated spin pair can be enhanced by adjusting the spinning speed such that nω_r = ω_Δ^iso, where n is an integer, ω_r is the spinning speed, and ω_Δ^iso is the difference between isotropic shifts. When this condition, termed rotational resonance, is satisfied, a broadening or a splitting of the normally sharp resonance lines is observed. In addition, rapid exchange of Zeeman order between the dipolar coupled spins is seen. This method holds promise for the measurement of through space dipolar couplings and thus internuclear distances in polycrystalline solids.     

Characterization of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Synthesized Using a CO2 Laser by Silicon-29 Magic Angle Spinning NMR and ESR

The structure of silicon carbide–silicon nitride (SiC–Si₃N₄) composite particles synthesized using a CO₂ laser was studied by magic angle spinning nuclear magnetic resonance (MAS-NMR) and electron spin resonance (ESR). The structure around Si atoms changed by introducing N. C atoms around Si were substituted by N atoms, and N-rich configurations around Si atoms increased stepwise as the N content increased. The low N content composite particles consisted of mainly SiC phase containing dissolved N. N atoms were partly present in β-SiC microcrystal and partly in the grain boundary layer in the particle. N atoms were tetrahedrally surrounded by four Si atoms in β-SiC microcrystal and were trivalent state bonded to three Si atoms in the grain boundary layer. The high N content particles consisted of SiC, Si₃N₄, and amorphous phases, whose amount depended on N content.     

导流环倾角对汽轮机排汽缸气动性能影响的研究

以某300MW汽轮机为研究对象,应用Fluent软件对不同来流条件下的排汽缸进行三维数值模拟,分析导流环倾角变化对排汽缸性气动性能影响。结果表明:在扩压管导流环轴向长度不变的情况下,随着导流环倾角的不断增大,总压损失系数和静压恢复系数呈单调变化。导流环倾角在20~30°区间时,扩压管的性能处于平缓趋势。排汽缸来流有较大的旋流有利于提高排汽缸的气动性能,而较小的旋流则会带来一定的流动损失。     

Characterization of ethylene-1-butene copolymer by differential scanning calorimetry and 13C-NMR spectroscopy

Two kinds of ethylene-1-butene copolymers that were produced by the different procedures, that is, the slurry and the high-pressure polymerizations, were characterized by differential scanning calorimetry (DSC) and carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopy. The melting points of both copolymers were found to be different in spite of the same 1-butene content. It was deduced that this phenomenon depended upon the subtly different chain structures between these two copolymers from the tetrad monomer sequence analysis by ¹³C-NMR method. In addition, the behavior of the composition fractionation by temperature rising elution technique was also considered to be affected by the chain structures.     

用13C-NMR表征高乙烯含量乙烯-丙烯无规共聚物的结构与性能

采用淤浆聚合法,使用3种聚丙烯催化剂制备了高乙烯含量乙烯-丙烯无规共聚物,并采用核磁共振碳谱对共聚物结构和性能进行了表征。结果表明:在相同聚合条件下,使用二醇酯化合物作为内给电子体的ND催化剂同已商业化的两种Ziegler-Natta催化剂CAT1和CAT2聚合得到的乙烯-丙烯无规共聚物中的乙烯摩尔分数接近,为75%~78%;使用ND催化剂聚合得到的乙烯-丙烯无规共聚物链段中乙烯-丙烯单元序列分布更均匀;使用ND催化剂聚合得到的乙烯-丙烯无规共聚物中橡胶相相对含量高于采用CAT1和CAT2催化剂。     

1H-NMR/13C-NMR studies of branched structures in PVC obtained at atmospheric pressure

Summary The ¹H-NMR-spectra of raw poly (vinyl chloride) obtained at atmospheric pressure (U-PVC) have revealed the presence of high concentrations of branches. The content of labile chlorine was determined by reaction with phenole in order to estimate the branch points with tertiary chlorine. The branch length of reductively dehalogenated U-PVC by¹³C-NMR analysis have provided evidence for both short chain branches including chloromethyl groups and 2.4-dichloro-n-butyl groups and long chain branching. For a number of U-polymers the total amount of branching ranges from 7.5 to 13.5/1000 C. The ¹³C-NMR measurements point to a ratio of methyl/butyl branches of 1 1 and short chains/long chains of 6 1 .     

13C-NMR study of ethylene/1-hexene and ethylene/1-octene copolymers obtained using homogeneous catalysts

Summary This study employed the ¹³C-NMR spectroscopy to investigate the influence of the increase of the comonomer concentration on the microstruture of ethylene/1-hexene and ethylene/1-octene copolymers obtained by the use of MeSiCp₂ZrCl₂, Cp₂ZrCl₂, Et[Ind]₂ZrCl₂ and [Ind]₂ZrCl₂ catalysts. For both comonomers butyl or hexyl branches were isolated between ethylene blocks. As the -olefin concentration in the copolymer increased, butyl or hexyl branches became closer, some of them, separated by only one or two ethylene units. Incorporation of -olefin in the copolymer was higher for the bridged catalysts, MeSiCp₂ZrCl₂, and Et[Ind]₂ZrCl₂ than for the unbridged ones. The -olefin size did not seem to effect its reactivity towards ethylene.     

Characterization of LLDPE/LLDPE-g-AA Blends by Contact Angle and FT-IR Methods

Abstract

Blends of linear low density polyethylene (LLDPE) and linear low density polyethylene-grafted-acrylic acid (LLDPE-g-AA) were prepared by melt mixing. The surface of films with different content LLDPE-g-AA were characterized through contact angle measurements and FT-IR spectroscopy. The contact angles of water and glycerol on films surfaces of LLDPE/LLDPE-g-AA blends decrease with increase of LLDPE-g-AA. From FT-IR spectra of the blends, the carbonyl peak strength on the films surface was calculated. It was found that larger the carbonyl peak strength, the lower the value contact angle for LLDPE/LLDPE-g-AA blends.     

用元素和光谱(FTIR和13C-NMR)分析研究橄榄渣与谷物秸秆废弃物堆肥生成的黄腐酸特性

利用元素分析、官能团分析和光谱(FTIR,13C-NMR)分析的方法,研究了以橄榄渣和谷物秸秆为原料堆肥过程中生成的黄腐酸,旨在跟踪堆肥的成熟度。由堆肥中萃取的黄腐酸的总氮、酸性官能团和酚羟基的含量很高,这一特性可能来源于原料的高度腐殖化并形成了缩合度较高的腐植酸复合物。FTIR,13C-NMR分析结果表明,原料中醇羟基和脂肪结构减少而芳香结构增加了,证实了上述推论。研究结果表明,堆肥在12个月后最终产品的组成达到稳定,而黄腐酸的含量可以作为堆肥成熟程度及其农业应用价值的评价指标。     

低汽气比高温变换催化剂的表征及应用

通过对ICI71－4和LB型低汽气比高温变换催化剂在侧线试验装置上使用前后的结构进行测定，探讨适用于低汽气比合成氨工艺流程的催化剂的表征特性。     

Separation and Structural Characterization of Lignin from Hybrid Poplar Based on Complete Dissolution in DMSO/LiCl

In this paper, the physicochemical properties and structural features of six lignin preparations separated with a total dissolution of ball-milled wood in dimethyl sulfoxide and lithium chloride (DMSO/LiCl) followed by extraction with ethanol/water were investigated. These isolated lignin fractions were characterized using wet chemical analysis, FT-IR, and ¹H and¹³C-NMR techniques. Experimental results showed that separated lignin preparations were relatively free of associated polysaccharides. These lignin fractions were classified as guaiacyl-syringyl lignin type: mainly composed of guaiacyl units with noticeable amounts of syringyl units and fewer p-hydroxyphenyl units. The molar ratio of non-condensed guaiacyl units to syringyl units (G/S) decreased as the ratio of LiCl to poplar weight increased. The results also showed that these lignin preparations consisted mainly of β-O-4 ether bonds combined with small quantities of β-β′ and β-5 carbon-carbon linkages. Furthermore, considerable amounts of esterified p-hydroxybenzoic acids and minor amounts of esterified p-coumaric acid were also detected in these lignin fractions.     

Molecular Level Characterisation of the Surface of Carbohydrate-Functionalised Mesoporous silica Nanoparticles (MSN) as a Potential Targeted Drug Delivery System via High Resolution Magic Angle Spinning (HR-MAS) NMR Spectroscopy

Atomistic level characterisation of external surface species of mesoporous silica nanoparticles (MSN) poses a significant analytical challenge due to the inherently low content of grafted ligands. This study proposes the use of HR-MAS NMR spectroscopy for a molecular level characterisation of the external surface of carbohydrate-functionalised nanoparticles. MSN differing in size (32 nm, 106 nm, 220 nm) were synthesised using the sol-gel method. The synthesised materials displayed narrow particle size distribution (based on DLS and TEM results) and a hexagonal arrangement of the pores with a diameter of ca. 3 nm as investigated with PXRD and N₂ physisorption. The surface of the obtained nanoparticles was functionalised with galactose and lactose using reductive amination as confirmed by FTIR and NMR techniques. The functionalisation of the particles surface did not alter the pore architecture, structure or morphology of the materials as confirmed with TEM imaging. HR-MAS NMR spectroscopy was used for the first time to investigate the structure of the functionalised MSN suspended in D₂O. Furthermore, lactose was successfully attached to the silica without breaking the glycosidic bond. The results demonstrate that HR-MAS NMR can provide detailed structural information on the organic functionalities attached at the external surface of MSN within short experimental times.     

CO/FTIR Spectroscopic Characterization of Pd/ZnO/Al2O3 Catalysts for Methanol Steam Reforming

An as-synthesized 8.8wt% Pd/ZnO/Al₂O₃ catalyst was either pretreated under O₂ at 773 K followed by H₂ at 293 K or under H₂ at 773 K to obtain, respectively, a supported metallic Pd° catalyst (Pd°/ZnO/Al₂O₃) or a supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃). Both catalysts were studied by CO adsorption using FTIR spectroscopy. For the supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃), exposure to a mixture of methanol and steam, simulating methanol steam reforming reaction conditions, does not change the catalyst surface composition. This implies that the active sites are PdZn alloy like structures. The exposure of the catalyst to an oxidizing environment (O₂ at 623 K) results in the break up of PdZn alloy, forming a readily reducible PdO with its metallic form being known as much less active and selective for methanol steam reforming. However, for the metallic Pd°/ZnO/Al₂O₃ catalyst, FTIR results indicate that metallic Pd° can transform to PdZn alloy under methanol steam reforming conditions. These results suggest that PdZn alloy, even after an accidental exposure to oxygen, can self repair to form the active PdZn alloy phase under methanol steam reforming conditions. Catalytic behavior of the PdZn/ZnO/Al₂O₃ catalyst also correlates well with the surface composition characterizations by FTIR/CO spectroscopy.     

Preliminary Characterization of Gel Precursors and Their High-Temperature Products by 27Al Magic-Angle Spinning NMR

The environment of the Al atom in alumina gels, single-phase and diphasic mullite gels, and their transformation products was studied by ²⁷Al magic-angle spinning nuclear magnetic resonance (MASNMR). Alumina gels made from inorganic and organic precursors showed exactly the same ²⁷Al MASNMR spectra. Heat treatment of gels at 500°C caused artial conversion of octahedral Al to tetrahedral Al. The Al in single-phase mullite gel appears to be highly ordered compared to that in diphasic mullite gel.     

玉米秸秆木质素降解过程的CP/MAS 13CNMR和SEM表征

利用黄孢原毛平革菌对玉米秸秆木质素进行降解处理,通过CP/MAS 13 CNMR和SEM研究降解过程中木质素的结构变化。CP/MAS 13 CNMR结果表明:玉米秸秆木质素降解过程中,作为木质素结构单元主要连接方式的β-O-4键基本上没有被降解;木质素单位苯环的甲氧基含量稍有增加;S/G值降低,推断反应过程中紫丁香基优先参与反应。SEM结果表明:降解后的木质素空穴增多且增大、颗粒物质减少,主要是由于酶解木质素中大量碳水化合物的降解所致;比木质素更容易降解的纤维素和半纤维素也存在于样品中。CP/MAS 13 CNMR为木质纤维原料结构的定性和初步定量提供了可能,是传统定量表征手段的有力补充,具有一定的研究意义。     

天然竹纤维的固态核磁共振谱表征

利用固态核磁共振碳谱分析研究了天然竹纤维的结晶结构,并与常规的天然纤维素纤维苎麻、亚麻和棉纤维进行了比较。研究表明竹纤维的结晶度、晶粒尺寸与苎麻相似,大于棉纤维和亚麻纤维。利用13C NMR分析计算出了竹纤维中纤维素的晶型含量,结果显示,竹纤维的晶型与棉纤维、苎麻和亚麻相似,纤维素Ⅰβ占优势。利用核磁共振谱计算的几种纤维素纤维的结晶度和晶粒尺寸小于利用X射线衍射计算的结果,只有对于高结晶度的纤维如竹纤维和苎麻偏差才比较小,主要原因在于NMR分析对小范围的有序更为敏感,只有晶区内的材料才能看作结晶区。