High resolution solid-state NMR and DSC study of poly(ethylene glycol) silicate hybrid materials via sol-gel process

Hybrid materials incorporating poly(ethylene glycol) (PEG) with tetraethoxysilane (TEOS) via a sol-gel process were studied for a wide range of compositions of PEG by DSC and high resolution solid-state C-13- and Si-29-NMR spectroscopy. The results indicate that the microstructure of the hybrid materials and the crystallization behavior of PEG in hybrids strongly depend on the relative content of PEG. With an increasing content of PEG, the microstructure of hybrid materials changes a lot, from intimate mixing to macrophase separation. It is found that the glass transition temperatures (T-g) (around 373 K) of PEG homogeneously embedded in a silica network are much higher than that (about 223 K) of pure PEG and also much higher in melting temperatures T-m (around 323 K) than PEG crystallites in heterogeneous hybrids. Meanwhile, the lower the PEG content, the more perfect the silica network, and the higher the T-g of PEG embedded in hybrids. An extended-chain structure of PEG was supposed to be responsible for the unusually high T-g of PEG. Homogeneous PEG-TEOS hybrids on a molecular level can be obtained provided that the PEG. content in the hybrids is less than 30% by weight. (C) 1998 John Wiley & Sons, Inc.

MICROSTRUCTURE ANALYSIS OF 3 SEGMENTED COPOLYMERS CONTAINING POLYDIMETHYLSILOXANE BY SOLID-STATE HIGH-RESOLUTION NMR

The microstructure of two bicomponent and one tricomponent segmented copolymers, based on polydimethylsiloxane, poly(p-hydroxystyrene) or/and polysulfone, were investigated using an extended Goldman-Shen pulse sequence, proton spin-spin relaxation measurements, and C-13 and Si-29 NMR spectra. The results indicate that there exist four phases with different sizes, components and morphological structure in the segmented copolymers studied in this work, i. e., a rigid-chain phase of very slow motion, a rigid-chain-rich phase of slow motion, a flexible-chain-rich phase of fast motion and a flexible-chain phase of faster motion. The sizes of different domains, calculated from the spin diffusion rates, are about 50-100 angstrom for the flexible-chain-rich phase of fast motion and 200-300 angstrom for the flexible-chain phase of faster motion. The relative quantities of polydimethylsiloxane in the flexible-chain phase of fast motion are slightly different in different kinds of segmented copolymers.

用~(29)Si固体核磁共振方法研究M—ZSM-5分子筛

杂原子ZSM-5分子筛对某些特定的催化反应具有很高的活性和选择性,因而杂原子在分子筛中的存在状态成为人们十分关注的问题,作者曾用许多结构研究方法对杂原子ZSM-5分子筛进行了表征。本文用~(29)Si MAS NMR方法研究了M-ZSM-5 (M=Ga、B、Zn、Ni)分子筛杂原子的存在状态。

A29 NMR spin-lattice relaxation study of paramagnetics -doped orthosilictes

A ~si MAS NMR study of spin-lattice relaxation behaviour in paramagnetic-doped crystalline silicates was undertaken, using synthetic magnesium orthosilicate (forsterite) and synthetic zinc orthosilicate (willemite) doped with 0.1% to 20% of Co(II), Ni(II), or CU(II), as experimental systems. All of the samples studied exhibited a longitudinal magnetization return to the Boltzmann distribution of nuclear spin states which followed a stretched-exponential function of time: Y=exp [- (tjTn) n], O

Tailoring surface properties and structure of layered double hydroxides using silanes with different number of functional groups

Four silanes, trimethylchlorosilane (TMCS), dimethyldiethoxylsilane (DMDES), 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS), were adopted to graft layered double hydroxides (LDH) via an induced hydrolysis silylation method (IHS). Fourier transform infrared spectra (FTIR) and 29Si MAS nuclear magnetic resonance spectra (29Si MAS NMR) indicated that APTES and TEOS can be grafted onto LDH surfaces via condensation with hydroxyl groups of LDH, while TMCS and DMDES could only be adsorbed on the LDH surface with a small quantity. A combination of X-ray diffraction patterns (XRD) and 29Si MAS NMR spectra showed that silanes were exclusively present in the external surface and had little influence on the long range order of LDH. The surfactant intercalation experiment indicated that the adsorbed and/or grafted silane could not fix the interlamellar spacing of the LDH. However, they will form crosslink between the particles and affect the further surfactant intercalation in the silylated samples. The replacement of water by ethanol in the tactoids and/or aggregations and the polysiloxane oligomers formed during silylation procedure can dramatically increase the value of BET surface area (SBET) and total pore volumes (Vp) of the products.

Controlled combustion synthesis and properties of fine-particle NASICON materials

Fine-particle NASICON materials, Na1+xZr2P3-xSixO12 (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5), have been prepared by controlled combustion of an aqueous solution containing stoicthiometric amounts of sodium nitrate, zirconyl nitrate, ammonium perchlorate, diammonium hydrogen phosphate, fumed silica and carbonohydrazide. Formation of NASICON has been confirmed by powder XRD, Si-29 NMR and IR spectroscopy. These NASICON powders are fine (average agglomerate size 5-12 mum) with a surface area varying from 8 to 30 m2 g-1. NASICON powders pelletized and sintered at 1100-1200-degrees-C for 5 h achieved 90-95% theoretical density and show fine-grain microstructure. The coefficient of thermal expansion of sintered NASICON compact was measured up to 500-degrees-C and changes f rom -3.4 x 10(-6) to 4.1 x 10(-6) K-1. The conductivity of Sintered Na3Zr2PSi2O12 compact at 300-degrees-C is 0.236 OMEGA-1 cm-1.

Stable ordered mesoporous silica materials templated by high-temperature stable surfactant micelle in alkaline media

Ordered hexagonal mesoporous silica material (JLU-30) has been successfully synthesized in alkaline media at high temperature (> 160 degreesC, using cationic (1,3-dimethyl-2-imidazolidin-2-ylidene)hexadecylmethyl-ammonium bromide (DIHAB) as a template, and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, differential thermal analysis (DTA), and thermogravimetric analysis (TG), as well as Al-27 and Si-29 nuclear magnetic resonance (NMR) spectroscopy. Mesoporous JLU-30 shows much higher hydrothermal stability than MCM-41. Si-29 NMR spectra indicate that the pore walls of JLU-30 samples synthesized at high temperature (160 degreesC) are fully condensed, giving a Q(4)/Q(3) ratio as high as 6.2. In contrast, MCM-41 synthesized at relatively low temperature (100 degreesC) shows the Q(4)/Q(3) + Q(2) ratio at 1.1. Such unique structural feature might be responsible for the observed highly hydrothermal stability of the mesoporous silica materials (JLU-30).

Conductive polyaniline/silica hybrids from sol-gel process

A hybrid material with a conductive organic network in an inorganic matrix has been prepared by in-situ hydrolysis/polycondensation of TEOS in an aqueous solution of a solubilized polyaniline. Due to intense hydrogen bonding (indicated by Si-29 NMR and FTIR) the conductive polymer is very well dispersed in the silica matrix. The Figure shows SEM images of a 46/54 wt.-% hybrid at two temperatures (left 20 degreesC, right 100 degreesC).

非碱性介质中全硅分子筛的合成与表征

在非碱性介质中,F-离子存在下,采用水热方法研究了全硅分子筛的合成。以三丙胺、胆碱、三亚乙基二胺和哌嗪为模板剂,合成出具有MFI结构(ZSM-5型)的全硅分子筛。全硅Theta-1和ZSM-39的模板剂分别为1,6-已二胺和四甲基溴化铵。~(29)Si MAS NMR研究结果表明,该体系得到的全硅分子筛具有结晶度高和缺陷少的特点。

甲基氢硅氧烷/二甲基硅氧烷二元共聚物及其齐聚氧化乙烯接枝物的合成

本文采用质子酸催化剂合成出含Si-H键的线型聚(甲基氢硅氧烷/二甲基硅氧烷)中间体。讨论了体系中微量水、封端剂用量及产物处理方法对聚合物分子量的影响。将此中间体与α-烯丙基齐聚乙二醇甲醚反应,NMR和IR结果均表明得到了带有氧化乙烯结构侧链的硅氧烷接枝共聚物。

晋北高岭石及其热产物的矿物物理学研究

通过对晋北地区高岭石及其热产物的研究，笔者主要得到了以下几点结论：1、晋北煤矸石是一种优质的高岭石，Fe、Ti含量低，结晶度高，晶体主要呈片状形态，具有较好的开发前景，应打破仅仅局限于陶瓷工业的局面。而P-1高岭石因Fe、Ti含量高，质量差。2、在高岭石受热脱羟过程中，部分羟基一直到850℃才完全脱失。3、在高岭石-莫来石反应系列中，存在SiO_2与Al_2O_3的分凝，SiO_2与Al_2O_3反应生成莫来石是莫来石的主要形成途径，Al-Si尖晶石与SiO_2反应生成莫来石只是一个次要途径。4、在高岭石热处理产物的研究中首次测到了-70ppm附近的Al-Si尖晶石的~(29)Si MAS NMR谱峰，Al-Si尖晶石是一个不稳定相，存在的温度范围大约为850-1000℃，随着温度升高，它将转变为莫来石。5、高岭石的980℃放热峰归因于在高岭石受热相变过程中，莫来石、方英石、γ-Al_2O_3的晶出。6、在煤矸石中，Fe主要以Fe~(2+)置换Al~(3+)形式存在，其次是部分Fe~(2+)被吸附在高岭石表面；而在P-1高岭石中，Fe主要以Fe~(3+)、Fe~(2+)置换Al~(3+)及杂质氧化物的形式存在。7、以前国内一些学者提出的所谓新矿物—“偏岭石”，笔者认为很可能是高岭石受煤自然烘烤形成的变高岭石。

Textural and structural properties of bioactive glasses in the system CaO-SiO2

Gel-derived CaO-SiO2 binary glasses of CaO mole fractions 0. 2, 0.3 and 0. 4 have been prepared and characterised. Pore diameter specific pore volume, skeletal density and porosity were found to increase with increasing CaO-content, whereas a concomitant decrease in specific surface area was observed. Si-29 NMR indicated that the 0.2 CaO mole fraction glass consisted of higly polymerized Q(4) and Q(3) silicate species, with some Q(2) units. With increasing CaO mole fraction, these silicate species became progressively depolymerised such that isolated SiO4 tetrahedra were detected within the 0.4 CaO glass matrix. Unusually, the glasses retained a proportion of Q(4) and Q(3) species as the CaO mole fraction was increased. All glass formulations exhibited in vitro bioactivity. The rate of hydroxyapatite precipitation followed the order 0.2 CaO > 0.4 CaO > > 0.3 CaO, an effect that is attributed to differences in the rate of dissolution of calcium from these glasses. This, in turn, appears to be dependent upon the proportion of Ca 21 participating in the formation of the glassy network.

Polytypism and Silicon carbide : a solid state nuclear magnetic resonance study

A survey of predominantly industrial silicon carbide has been carried out using Magic Angle Spinning nuclear magnetic resonance (MAS nmr); a solid state technique. Three silicon carbide polytypes were studied; 3C, 6H, and 15R. The 13C and 29 Si MAS nmr spectra of the bulk SiC sample was identified on the basis of silicon (carbon) site type in the d iff ere n t pol Y t Y pes • Out to 5.00 A fro mac en t r a lsi 1 i con (0 r carbon) atom four types of sites were characterized using symmetry based calculations. This method of polytype analysis was also considered, in the prelminary stages, for applications with other polytypic material; CdBr 2 , CdI 2 , and PbI 2 " In an attempt to understand the minor components of silicon carbide, such as its surface, some samples were hydrofluoric acid washed and heated to extreme temperatures. Basically, an HF removable species which absorbs at -110 ppm (Si0 2 ) in the 29 Si MAS nmr spectrum is found in silicon carbide after heating. Other unidentified peaks observed at short recycle delays in some 29 Si MAS nmr spectra are considered to be impurities that may be within the lattice. These components comprise less than 5% of the observable silicon. A Tl study was carried out for 29 Si nuclei in a 3C ii polytype sample, using the Driven Equilibrium Single-Pulse Observation of T1 (DESPOT) technique. It appears as though there are a number of nuclei that have the same chemical shift but different T1 relaxation times. The T1 values range from 30 seconds to 11 minutes. Caution has to be kept when interpreting these results because this is the first time that DESPOT has been used for solid samples and it is not likely in full working order. MAS nmr indicates that the 13C and 29 Si ~sotropic chemical shifts of silicon carbide appear to have a reciprocal type of relationship_ Single crystal nmr analysis of a 6H sample is accordance with this finding when only the resultant isotropic shift is considered. However, single crystal nmr also shows that the actual response of the silicon and carbon nuclear environment to the applied magnetic field at various angles is not at all reciprocal. Such results show that much more single crystal nmr work is required to determine the actual behavior of the local magnetic environment of the SiC nuclei.