Synthesis of SBS thermoplastic block copolymers in cyclohexane in the presence of diethylether used as a structure modifier

Diethylether (DEE) was used as a structure modifier during the synthesis of linear styrene-butadiene block copolymers of poly A-block-polyB-block-polyA type (SBS). The microstructures of synthesized polymers were analyzed, and the effect of DEE on polymerization kinetics was studied. Addition of DEE at 2 wt% concentration results in the highest styrene polymerization rate, while addition at 6 wt% concentration gives the highest butadiene polymerization rate. The vinyl content of the polybutadiene portion increases from 14 to 47% with an increase in the DEE concentration from 500 ppm to 10 wt% while thetrans- l,4 andcis-1,4 isomers decrease. For SBS polymer synthesized via a sequential method, the addition of DEE as a structure modifier minimizes the crossover deficiency which would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymers made via a coupling method, the coupling efficiency appears to be constant in a range of DEE concentration from 500 ppm to 1 wt% before declining with a further increase in DEE.     

A kinetic study of the activated anionic polymerization of ε-caprolactam

The diversities existing among published kinetic studies on activated anionic polymerization of ε-caprolactam are closely examined. A kinetic model derived from a regular, linear reversible reaction mechanism is employed to explain the experimentally observed autocatalytic character of the polymerization system and to examine the dependence of the apparent activation energy on the experimental method. Several existing kinetic models tested with our experimental data show that the autocatalytic type rate equation best describes the polymerization process.     

Miscibility, crystallization and morphologies of syndiotactic polystyrene blends with isotactic polystyrene and with atactic polystyrene

Two-component blends of differing polystyrene (PS), one syndiotactic (sPS) and the other isotactic (iPS) or atactic (aPS), were discussed. The phase behavior, crystallization and microstructure of binary polystyrene blends of sPS/iPS and sPS/aPS with a specific composition of 5/5 weight ratio were investigated using optical microscopy (OM), differential scanning calorimetry, wide-angle X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM). Based on the kinetics of enthalpy recovery, complete miscibility was found for the sPS/aPS blends where a single recovery peak was obtained, whereas phase separation was concluded for the sPS/iPS blends due to the presence of an additional recovery shoulder indicating the heterogeneity in the molten state. These findings were consistent with OM and SEM observations; sPS/iPS exhibits the dual interconnectivity of phase-separated phases resulting from spinodal decomposition.Both iPS and aPS have the same influence on the sPS crystal structure, i.e., dominant β-form sPS and mixed α-/β-form sPS obtained for melt-crystallization at high and low temperatures respectively, but imperfect α-form sPS developed when cold-crystallized at 175 °C. Co-crystallization of iPS and sPS into the common lattice was not observed regardless the thermal treatments, either cold or melt crystallization. Due to its slow process, crystallization of iPS was found to commence always after the completion of sPS crystallization in one-step crystallization kinetics. Segregation of rejected iPS component during sPS crystallization was extensively observed from TEM and SEM images which showed iPS pockets located between sPS lamellar stacks within spherulites, leading to the interfibrillar segregation, which was similar with that observed in the sPS/aPS blends. The addition of iPS (or aPS) component will reduce the overall crystallization rate of the sPS component and the retardation of crystal growth rates can be simply accounted by a dilution effect, keeping the surface nucleation intact. The phase-separated structure in the sPS/iPS blend shows a negligible effect on sPS crystallization and the signature of phase separation disappears after sPS crystallization. Depending on the relative dimensions of the segregated domains and iPS lamellar nucleus, subsequent crystallization of iPS can proceed to result in a crystalline/crystalline blend, or be inhibited to give a crystalline/amorphous blend morphology similar with that of sPS/aPS blends.     

The adsorption of dyes from aqueous solution using diatomite

Raw diatomite was calcined at 450 °C for dyes removal from aqueous solution. SEM and FTIR analysis show that the raw diatomite contains organic impurities, which are removed after the calcination. The impurities removal decreases the specific surface area and increases the average pore diameter of raw diatomite, while improves its adsorption capability of dyes. The adsorption isotherm and kinetics experiments of methylene blue onto calcined diatomite were then carried out to investigate the adsorption property. It shows that the adsorption capacity of methylene blue is about 50 mg/g. The adsorption isotherm was fitted by the Langmuir, Freundlich and Redlich-Peterson models, which reveals that the Redlich-Peterson isotherm is the best one. Two kinetic models, pseudo-first order and pseudo-second order, were rearranged for expediently investigating the adsortpion mechanisms. Fitting results show that the pseudo-first-order model is better in describing the adsorption process.     

一种用于气液间传质的新型轴流式叶轮

一种用于气液间传质的新型轴流式叶轮黄庆民林齐浩李启恩（华南理工大学化学工程研究所，广州５１０６４１）关键词气液传质轴流式叶轮１前言在液体搅拌器中，轴流式叶轮由于功耗较小且泵吸量较大而被广泛采用。在气液两相搅拌器中，由于轴流式叶轮有气泛问题，一般均采...     

High temperature polymerization of propylene catalyzed by MgCl2‐supported Ziegler–Natta catalyst with various cocatalysts

Four cocatalysts, referred to as ethylaluminoxanes, were synthesized by the reaction between triethylaluminium (AIEt₃) and water under various molar ratios of H₂O/Al at ?78°C. Aluminoxanes were used as cocatalysts for a MgCl₂‐supported Ziegler–Natta catalyst for propylene polymerization at temperatures ranging from 70 to 100°C. When the polymerization was activated by AlEt₃, the activity as well as the molecular weight and isotacticity of the resulting polymer gradually dropped as the temperature varied from 70 to 100°C. When ethylaluminoxane was employed as the cocatalyst, good activity and high molecular weight and isotacticity were obtained at 100°C. Furthermore, when the cocatalyst varied from AlEt₃ to ethylaluminoxane, the atactic fraction and polymer fraction with moderate isotacticity decreased and the high isotactic fraction slightly increased, which indicated that the variation of the cocatalyst significantly affects the isospecificity of active sites. It was suggested that the reactivity of the Al‐Et group and the size of the cocatalyst were correlated to the performance of the Ziegler–Natta catalyst at different temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1978–1982, 2006     

A novel high-performance counter electrode for dye-sensitized solar cells

A novel Pt counter electrode for dye-sensitized solar cells (DSC) was prepared by thermal decomposition of H₂PtCl₆ on NiP-plated glass substrate. The charge-transfer kinetic properties of the platinized NiP-plated glass electrode (Pt/NiP electrode) for triiodide reduction were studied by electrochemical impedance spectroscopy. Pt/NiP electrode has the advantage over the platinized FTO conducting glass electrode (Pt/FTO electrode) in increasing the light reflectance and reducing the sheet resistance leading to improve the light harvest efficiency and the fill factor of the dye-sensitized solar cells effectively. The photon-to-current efficiency and the overall conversion efficiency of DSC using Pt/NiP counter electrode is increased by 20% and 33%, respectively, compared to that of using Pt/FTO counter electrode. Examination of the anodic dissolution and the long-term test on the variation of charge-transfer resistance indicates the good stability of the Pt/NiP electrode in the electrolyte containing iodide/triiodide.     

Presumed joint probability density function model for turbulent combustion

A presumed joint probability density function (pdf) model of turbulent combustion is proposed in this paper. The turbulent fluctuations of reactant concentrations and temperature are described using a presumed joint pdf of three-dimensional Gaussian distribution based on first and second-order moments of reactant concentration and temperature. Mean reaction rates in both premixed and diffusion combustion are obtained by mean of integration under the presumed joint pdf. This model is applied to predict turbulent premixed combustion of sudden-expansion flow and turbulent jet diffusion methane/air flame. For turbulent premixed combustion, the predicted results of temperature distribution and maximum temperature using the proposed model agree better with the experiment than that using the conventional eddy-breakup (EBU)-Arrhenius model. For the turbulent jet diffusion methane/air flame, the predicted results of velocity, temperature and species concentrations using the proposed model, the Arrhenius, EBU-Arrhenius, and laminar flamelet models are compared with experiment data. Results obtained with the presumed pdf model and that obtained by the laminar flamelet model both agree well with experiments, while results using the other models have a significant difference. The presumed joint pdf model is used to predict the NO formation process, which also agrees well with the experiment data. A unified turbulent combustion model, in which both effects of turbulent diffusion and chemical dynamics are considered, is established for both premixed and diffusion combustion, especially for the process of NO formation.     

高热稳定性和可逆交联性质的含新型偶氮发色团电光聚合物的研究

制备了两种新型的分别含有以三苯胺为电子给体的偶氮类发色团作为特征活性官能团和3-呋喃甲酸及受保护的马来酰亚胺的可交联型聚合物体系．通过研究表明利用该制备方法，发色团在聚合物中的含量得到了极大的提高，分别达到32．1％（NLO1_P1）和44．4％（NLO1_P2）．该聚合物体系以“DielsAlder”[4＋2]环加成反应作为其交联特征，具有高温非交联、低温交联的特点，其过程与以往的热交联型聚合物相反，可解决传统电光交联聚合物中存在的热交联对极化效率影响的问题并用热失重分析法（TGA）和差示扫描量热法（DSC）分析了这一过程．此外DA交联型聚合物，不需要引入额外的助交联剂，克服了传统热交联聚合物分离难的问题，最大程度的保证了材料的纯度．