Reversible addition fragmentation transfer (RAFT) polymerization of styrene in a miniemulsion: A mechanistic investigation

The RAFT polymerization of styrene in miniemulsion using 1-phenylethyl phenyl-dithioacetate (PEPDTA) as a RAFT agent was investigated, in attempt to reveal the mechanism for the often observed inferior performance such as low polymerization rate, broad molecular weight distribution and particle size distribution in the RAFT miniemulsion polymerization with regular levels of surfactant and co-stabilizer (1 wt% sodium dodecyl sulfate and 2 wt% hexadecane). It is strongly evident that a few of large oligomer particles consisting of oligomer, RAFT agent (RAFT agent refers to the original RAFT agent), and monomer would be formed in the early stage of the polymerization due to the superswelling of the first nucleated droplets. With the regular levels of surfactant and co-stabilizer, the observed low polymerization rate, broadened molecular weight distribution, slow conversion of the RAFT agent, lower N_p, and broadened particle size distribution could be well explained by the formation of these large oligomer particles and their prolonged existence. When the formation of the oligomer particles was suppressed by increasing surfactant and co-stabilizer levels and wise selection of types of RAFT agent, the molecular weight distribution could be narrowed to around 1.3 and particle size distribution could be close to that of the conventional non-living miniemulsion polymerization.     

Rheological study of poly(ethylene glycol)/poly(N‐isopropylacrylamide‐co‐2‐acrylamido‐2‐methylpropanesulphonic acid) semiinterpenetrating network formation

The formation of a series of semiinterpenetrating network (SIPN) hydrogels made by free‐radical copolymerization of N‐isopropylacrylamide (NIPA) and 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) with varying comonomer mole ratios, crosslinked with N,N′‐methylene‐bisacrylamide (MBAA) in the presence of poly(ethylene glycol) (PEG) with average molecular weight 6,000 g mol^?1 was studied via determination of complex viscosity, η*, using plate–plate rheometry. The isothermal time dependence of η* at various temperatures or the variation of η* with temperature of pregel solutions was utilized to detect the onset of gelation. The SIPN systems were compared with the corresponding gels made under the same conditions in the absence of PEG. The copolymer mainchain composition has a major effect on the time or temperature for onset of gelation and in particular gelation appears to be inhibited to some extent by MBAA when the AMPS/NIPA mole ratio in the pregel solution exceeds 0.5. The presence or absence of PEG in pregel solutions has a lesser effect on gelation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2083–2087, 2004     

TiO_2薄膜光催化降解甲基橙反应动力学研究

以甲基橙为模型污染物、TiO2薄膜为光催化剂,在自制的光催化反应器上进行了光催化降解反应实验,主要研究了甲基橙初始浓度(c0)和紫外光光照强度(I)对其光催化降解反应的影响。结果表明,该降解反应可用一级反应动力学方程进行描述,反应速率常数(k)与c0及光强I的关系分别为:k∝c0-1 4和k∝I0.65。     

Platinum particle size effect on the oxidative dehydrogenation of aqueous ethanol

The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m^–3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m^–3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity.     

外源紫杉醇作用下南方红豆杉细胞凋亡及其动力学研究

利用光学显微照相技术、细胞总DNA琼脂糖凝胶电泳和TUNEL标记等手段 ,研究了外源紫杉醇(Taxol)作用下南方红豆杉细胞的凋亡及其动力学。研究结果表明 ,外源紫杉醇能显著提高南方红豆杉细胞凋亡的速率和发生率 ,表明高浓度紫杉醇不利于细胞的生长。凋亡动力学研究对指导大规模植物细胞培养生产紫杉醇具有重要意义     

免水型生态卫生设施用降解菌的分离筛选

本文对免水型生态卫生设施中的生物填料及施有机肥农田的土壤进行了人类粪便降解菌的分离。筛选得到的各菌种在实验条件下，降解粪便效果较好，除臭除味，COD下降率在30％左右。其中在土壤中分离出来的9号菌，COD下降率达41％，全部菌种复合培养处理的下降率高达59％。结果表明，实验采用的分离筛选方法是比较有效的，筛选得到了具有较好降解效果的菌种，为降解菌的进一步试验打下了基础。     

甲醇羰基化法合成甲酸甲酯流程模拟

采用流程模拟的方法对甲醇羰基化法合成甲酸甲酯的进料条件及反应压力等工艺条件对反应强度、动力消耗等参数的影响给出了定量的分析结果 ,并提出了在过程设计和生产操作中根据甲酯产率及消耗确定适宜工艺参数的方法     

Rice husk ash filled natural rubber. I. Overall rate constant determination for the vulcanization process from rheometric data

Black rice husk ash (BRHA) and white rice husk ash (WRHA) were incorporated into natural rubber (NR) using a laboratory‐size two‐roll mill. A conventional vulcanization system (CV) was chosen and cure studies were carried out on a TI‐100 Curometer. The torque curves were obtained at 150, 160, 170, and 180°C. The overall rate and the apparent activation energy for the vulcanization process were calculated for each compound assuming that vulcanization follows first‐order kinetics. For comparison purposes, two commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N762), were also used. It was observed that addition of WRHA to NR compounds increased the cross‐linking rate and lowered the apparent activation energy more markedly than the other fillers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1194–1203, 2003