A study of the influence of the synthesis conditions upon the catalytic properties of silicoaluminophosphate molecular sieves

The skeletal isomerization of 1butene was performed over a series of silicoaluminophosphate molecular sieves with AEL structure (SAPO11). The results were compared with those obtained over an aluminophosphate molecular sieve (AlPO₄11). The three SAPO11 samples, with different acidic properties, were synthesized by either varying the chemical composition of the synthesis gel or by varying the preparation time of the aforementioned gel. The catalytic results indicate that irrespective of how the acidity of the SAPO11 samples is changed (viz., independently of the method elected to modify the acidic properties of the samples), a close parallelism between the selectivity towards the skeletal isomerization and the number of (moderate + strong) Brønsted acid sites (sites retaining pyridine above 623 K) was observed for the SAPO11 solids. These results, definitively, indicate the participation of these acid sites in the skeletal isomerization process.     

可紫外光固化聚氨酯乳液的合成与性能研究

对可紫外光固化的芳香族水分散性聚氨酯的合成与性能进行了初步的探讨。利用聚醚多元醇，甲苯二异氰酸酯和丙烯酸羟丙酯合成了稳定的可紫外光固化的水分散和性聚氨酯乳液。发现随着光照时间延长和丙烯酸羟丙酯用量的增加，所得聚氨酯薄膜的拉伸强度增加，断裂伸长率下降，在有机溶剂中的溶胀度也下降。     

Effects of jet-cooking conditions upon intrinsic viscosity and flow properties of starches

This work examined the sensitivity of intrinsic viscosity values of jet-cooked waxy maize starch to initial pH conditions and the effects of jet-cooker steam pressure parameters upon the intrinsic viscosity and flow viscosity values of four jet-cooked starches. Flow viscosities of the 10 wt % cooked starches and intrinsic viscosities in 90% DMSO-H₂O were the lowest when mixing and turbulence during steam jet-cooking was increased (i.e., by adjusting steam line pressure vs. pressure within the cooking chamber to allow greater amounts of steam to flow through the apparatus). The percent decreases of the intrinsic viscosity caused by the most severe cooking conditions compared to gentle cooking conditions were 52, 45, 32, and 12, respectively, for waxy maize, waxy rice, normal maize, and 70% high amylose maize starches. Initial pH values, from 3 to 10.5, of waxy maize starch had minor effects upon the intrinsic viscosity of the jet-cooked material. © 1996 John Wiley & Sons, Inc.

1 This is a U.S. Government work and, as such, is in the public domain in the United States of America.

     

聚甲基丙烯酸甲酯-g-聚乙二醇单甲醚的合成及水溶液性质研究

采用主链接枝法合成了梳形表面活性剂聚甲基丙烯酸甲酯-g-聚乙二醇单甲醚(PMMA-g-MPEG).利用红外光谱(IR)、核磁共振氢谱(1HNMR)和凝胶渗透色谱(GPC)对其结构进行了表征.分别对PMMA-g-MPEG水溶液的浊点、表面活性及流变性质进行了研究.实验结果表明:其浊点大于90℃;25℃时,其临界胶束浓度为0.4 g/L,临界胶束浓度时的表面张力为48.7 mN/m;稀溶液近似为牛顿型流体,浓溶液具有强烈的剪切变稀的行为和黏弹性.     

Analysis of phenol-formaldehyde resols by gel permeation chromatography

The chromatographic analysis of resol solutions in tetrahydrofuran solvent, by means of a set of columns packed with crosslinked polystyrene gels, has been carried out with adequate resolving power for a clear-cut qualitative or semiquantitative differentiation between various types of resols to be practicable. The resulting chromatograms, which show the distribution of different constituents by molecular size, could be interpreted by the use of reference substance and by calibrating the system with a number of compounds of known structures. The method has been used to investigate the way in which various reaction parameters (nature of catalysts, proportion of starting material, treatments undergone by the resols) affect the composition of resols. Different commercial products have been thus characterized. It has also afforded an insight into the progress of the polycondensation reaction as a function of time and helped to state the reactivity of different groups and unblocked ring positions. Thus, an hydroxymethyl group appears to be more reactive in the para than in the ortho position. Otherwise the reactivity of unblocked ring positions would be enhanced by an hydroxymethyl group in the ortho rather than para position.     

Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions

The relationship between the shape memory properties and thermomechanical cyclic conditions was investigated with a type of shape memory polyurethane (SMPU). The thermal and dynamic mechanical properties of the polyurethane were examined by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the SMPU exhibited good shape memory effects (SMEs) at deformation temperatures ranging from T_g to T_g + 25 °C. The strain recovery ratios increased with the increase of deformation speed and with the decrease in maximum strain. The recovery ratios also increased with increasing fixing speed. Therefore, in practical applications, in order to obtain better SMEs, the SMPU should be cooled to its frozen state as soon as possible after being deformed at a high temperature. The ‘fixity’ dramatically increased with the decrease in fixing temperature. To obtain optimal SMEs, the polymer has to be reheated up to the temperature at which the polymer deformed. In addition, the recovery ratios of the SMPU could increase slightly with the increase of recovery time. Copyright © 2004 Society of Chemical Industry     

Dependence of the strength properties of oriented linear polyethylene on the orienting conditions during stretching

Conclusions An analysis of the strength characteristics and lifetime of film-based fibres from linear polyethylene which have been subjected to orientation stretching after the development of a neck under various subsequent stretching regimes has been carried out.A regime of multistage zone stretching, carried out in four stages with a slight increase in orienting stress (by 5 MPa) after each preceding stage, is optimum from the point of view of attaining high strength, lifetime, and reproducibility of material mechanical properties.With a more abrupt increase in orienting force, the number of stretching stages can be reduced to 2 or 3. Specimens drawn in this way are not inferior in strength to specimens drawn to the same extent by regime I, but they have a lower lifetime because of intense mechanical degradation which they undergo in the extension under the larger orienting stress. Such regimes are less reproducible.A nonidentical character of failure for specimens stretched under gradual and under abrupt loading has been noted.Translated from Khimicheskie Volokna, No. 5, pp. 40–42, September–October, 1985.     

Differential scanning calorimetry of phenol–formaldehyde resols

Differential scanning calorimetry was used on a range of synthesized phenol–formaldehyde (PF) resols to discover relationships between formulation parameters or physical properties of resols, and their thermal behavior during cure. The thermograms showed either one or two exothermic reactions. The lower exothermic peak temperature varied between 98 and 129°C with changes in the free formaldehyde content. This exotherm is caused by the addition of free formaldehyde to phenolic rings. The upper exothermic peak temperature varied from 139 to 151°C, with the higher temperatures occurring when the formaldehyde-to-phenol molar ratio was low or the total amount of sodium hydroxide relative to phenol was high. These two factors led to resins which contain a somewhat higher level of unreacted ortho or para aromatic ring positions and no free formaldehyde. Consequently, condensation is probably not solely by the faster self-condensation through hydroxymethyl groups, but also includes the slower condensation of hydroxymethyl groups with unreacted ring positions. Gel times show trends with changes of formulation parameters somewhat similar to trends of the upper exothermic peak temperatures.     

海藻糖合成双酶体系酶性质及酶反应条件的研究

通过对自筛出的一株微球菌 (Microccusroseus)进行海藻糖合成酶的性质及海藻糖合成的酶反应条件的研究 ,建立了使用粗酶不经纯化 ,直接进行酶反应的工艺流程 ,此工艺有可能进一步降低海藻糖的成本。研究得到了酶反应的一系列优化条件 :2 0 %细胞悬液 ,2 5℃下用 3 %甲苯处理 1h ;然后在 1 0 0mmol/L缓冲液中 ,pH值 8 0、30℃下与 5 %淀粉液化液进行酶反应2 4h ,得到海藻糖转化率达 75 %。研究了该酶体系的性质 ,发现该反应体系不存在底物和产物抑制 ,但存在对其产生抑制的金属离子 ,同时发现海藻糖对该酶体系有异常的激活作用     

不同结构水性聚氨酯分散体的合成与性能研究

用不同结构不同分子质量的聚酯多元醇合成一系列水性聚氨酯分散体,探讨了其力学性能、黏度、粘附力和贮存稳定性,还分析了结晶性、扩链剂和硬段含量对水性聚氨酯性能的影响.结果表明,用PBA和PHA合成的水性聚氨酯具有较好的性能,适度的结晶性有利于提高粘附力,扩链交联剂在一定的比例范围才能保持分散液的稳定性,40%～46%硬段含量可以保证水性聚氨酯既有较好的力学性能和黏度,又有满足使用要求的干燥速度.     

酮醛改性水性丙烯酸酯树脂的合成及性能研究

以丙烯酸、丙烯酸酯、甲基丙烯酸酯等为基料，在过硫酸铵引发下，加入醛酮树脂进行改性聚合，合成了几种不同的酮醛改性的水溶性丙烯酸树脂，将上述树脂加入颜料、消泡剂、分散剂等，制成水性油墨，经测定其成膜性、耐磨性、耐水性等性能均达到水墨在印刷上所要求的标准。     

Effect of synthesis conditions on properties of poly(N-isopropylacrylamide) gels

Properties of poly(N-isopropylacrylamide) gels—equilibrium degree of swelling, shear modulus, effective crosslink density and clarity—depend significantly upon the conditions of synthesis. While it is well known that monomer and crosslinker concentrations affect gel properties, other variables are shown here to have significant effects on the properties of the resulting gels. Initiator type and concentration, synthesis temperature, mold geometry and polymerization time all significantly affect the properties, including the swelling degree. Evidence suggests that the microstructure of these gels is particularly sensitive to these variables.     

合成工艺条件对UFC性能的影响

以U(尿素)和高浓度F(甲醛)为反应原料,合成了UFC(脲醛树脂预缩液),并考察了反应原料配比、反应温度和反应时间对UFC性能的影响。研究结果表明:反应原料配比与UFC的稳定性密切相关,当n(F)∶n(U)≥5.0∶1.0时,可得到性能稳定的UFC;改变反应温度或反应时间,UFC的游离F含量和耐冷冻性波动较大;提高反应温度或延长反应时间对UFC的结构组成、分布基本上具有同等效应。     

Influence of the synthesis conditions on the properties of thermoplastic polyurethane elastomers

Thermoplastic polyurethane elastomers (TPUs) of constant composition were prepared by using the prepolymer method and by changing the reaction conditions (prepolymerization and chain‐extension time) to study the influence of these conditions on the final TPU properties. The TPUs were characterized by gel permeation chromatography, differential scanning calorimetry, strain–stress measurements, and contact‐angle measurements. To test the adhesion properties of the TPUs, poly(vinyl chloride) strips were bonded to each other by using TPU solutions and the T‐peel strength of the adhesive joints was measured. It was found that provided a threshold is crossed, the prepolymerization time markedly influences the final properties of the TPUs (viscosity of solutions, molecular weight, mechanical and adhesive behavior), whereas the chain extension time does not. Therefore, it is possible to prepare TPUs with specific properties by playing with the prepolymerization conditions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1590–1595, 2000     

Dependence of properties of swollen and dry polymer networks on the conditions of their formation in solution

A marked difference between the properties of networks first crosslinked and then swollen, and those synthesized in a solvent medium, has been shown. The present investigation was carried out using two different types of regular networks, polysiloxane and polyisocyanurate networks, which had different chain flexibilities, crosslinking densities, and intermolecular interactions. The concentration at which the network is formed v₀ and the quality of the solvent were varied over a wide range. It was found that with a decrease of v₀ from 1-0.05, the elastic modulus of both gels and dry networks obtained from these gels after removing the solvent decreased by a factor of 2–4 and equilibrium swelling decreased a few times.     

Dependence of carbon fiber morphology with deposition conditions

Carbon fibers with different morphologies including carbon nanotubes, short crossed carbon fibers, carbon nanofiber network structures, and nodular carbon fibers covered with carbon microbeads were synthesized using a floating catalyst method by changing the flow rate of xylene solution containing ferrocene, the concentration of ferrocene in xylene, and carrier gas. The general tendency is: Higher flow rate of xylene solution contributed to the formation of short crossed carbon fibers and deteriorated the graphitic crystalline of carbon fibers, which might play a critical role in their connection. Lower ferrocene concentration in xylene solution improved the graphitization of carbon nanofibers and changed the connection way of carbon nanofibers. Nodular carbon fibers covered with microbeads were obtained in N₂ ambience. Carbon nanotubes with well graphitic crystal were prepared with the concentration of ferrocene in xylene 1.5 g/100 ml, the flow rate of xylene solution 0.12 ml/min and hydrogen 150 ml/min.     

The effect of synthesis conditions on the physicochemical properties of magnesium aluminate materials

Magnesium aluminate-based materials were prepared by applying different methods: (i) mechanochemical milling of the initial mixture of magnesium and aluminium nitrate powders (in appropriate stoichiometric amounts) followed by heat treatment at temperatures of 650 °C and 850 °C and (ii) melting of the mixture of nitrate precursors at 240 °C followed by thermal treatment at 650 °C, 750 °C and 850 °C. The effect of synthesis method on the structure and morphology of the obtained solids was studied by using various techniques such as: nitrogen adsorption-desorption isotherms, powder XRD, IR spectroscopy and SEM. It was shown that the mechanochemical milling performed before calcination procedure leads to obtaining of nanocrystalline magnesium aluminate spinel phase at lower temperature of 650 °C in comparison with the method using thermal treatment only (at 750 °C). The obtained nanomaterials exhibit mesoporous structure.     

Effect of synthesis conditions on the rheological properties of styrene butyl acrylate copolymers

The chemical and physical properties of synthetic polymers depend strongly on the polymerization process. This fact is even more determinant when dealing with copolymers. Styrene/butyl acrylate copolymers were synthesized using an emulsion copolymerization process. The amount of initiator, emulsifier, and transfer agent were varied in a systematic way in order to establish the relationship between polymerization conditions and rheological properties of the molten copolymers. Rheological and molecular weight results show that the different polymerization conditions have important effects on the properties of the final copolymers mainly through the development of different sequence distributions of the monomeric units in the copolymer chain. These results have been interpreted in terms of the kinetic mechanisms that explain the emulsion copolymerization processes. Furthermore, the rheological characterization is used as an additional tool in establishing the different structure of the resulting copolymers.