Quasiliving Carbocationic Polymerization. XVII. Synthesis Of Poly (Styrene-β-Isobutylene-β-Styrene)

Poly(styrene-b-isobutylene-b-styrene) has been synthesized by sequential carbocationic polymerization under quasiliving conditions at -90°C. The quasiliving synthesis was effected by first continuously and slowly condensing gaseous isobutylene (IB) to a bifunctional initiating system (p-dicumyl chloride/TiCl₄) dissolved in a hexane-methylene chloride (60:40 v/v) mixture. After the quasiliving polyisobutylene (PIB) sequence had reached a desired molecular weight, styrene (St) was continuously and slowly added to produce the polystyrene (PSt) sequence. The products consisted of the target triblock. However, due to initiation by impurities and possibly to chain transfer to both IB and St, it also contained diblocks and small amounts of homopolymers. While the latter could be removed by selective fractionation, the triblocks and diblocks could not be separated. The mechanism of quasiliving polymerization leading to PIB/PSt blocks is discussed.     

UHPLC‐ESI‐MS/MS determination and pharmacokinetics of pinoresinol glucoside and chlorogenic acid in rat plasma after oral administration of Eucommia ulmoides Oliv extract

This study aimed to develop a specific UHPLC‐ESI‐MS/MS method for simultaneous determination and pharmacokinetics of pinoresinol glucoside and chlorogenic acid in rat plasma after oral administration of Eucommia ulmoides . The chromatographic separation was achieved on a Hypersil GOLD column with gradient elution by using a mixture of 0.1% formic acid aqueous solution and acetonitrile as the mobile phase at a flow rate of 200 μL/min. A tandem mass spectrometric detection was conducted using multiple‐reaction monitoring via an electrospray ionization source in negative ionization mode. Samples were pre‐treated by a single‐step protein precipitation with acetonitrile, and bergenin was used as internal standard. After oral administration of 3 mL/kg E. ulmoides extract in rats, the maximum plasma concentrations of pinoresinol glucoside and chlorogenic acid were 57.44 and 61.04 ng/mL, respectively. The times to reach the maximum plasma concentration were 40.00 and 23.33 min for pinoresinol glucoside and chlorogenic acid, respectively. The intra‐ and inter‐day precision (RSD) values for the two analytes were <2.46 and 5.15%, respectively, and the accuracy (RE) values ranged from −12.76 to 0.00. This is the first study on pharmacokinetics of bioactive compounds in rat plasma after oral administration of E. ulmoides extract.     

Green synthesis of Ni‐Cu‐Zn ferrite nanoparticles using tragacanth gum and their use as an efficient catalyst for the synthesis of polyhydroquinoline derivatives

Ni_0.35Cu_0.25Zn_0.4Fe₂O₄ MNPs were synthesized using tragacanth gum as biotemplate and Metals nitrate as the metal source by the sol–gel method. The sample was characterized by powder X‐ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDX). The nanoparticles exhibit ferromagnetic behaviour at room temperature, with a saturation magnetization of 52.76 emu/g and a coercivity of 80.14 Oe. Thereupon, Ni‐Cu‐Zn ferrite nanoparticles as an efficient catalyst was used for the synthesis of polyhydroquinoline derivatives via multi‐component reactions under microwave irradiation. Simple work‐up, mild reaction conditions, short reaction times, use of an economically convenient catalyst, and excellent product yields are the advantageous features of this method. The catalyst could easily be recycled and reused few times without noticeable decrease in catalytic activity.     

La relation structure chimique–propriétés physiques des galactomannanes extraits de la caroube

Carob galactomannan fine chemical structure is closely related to the physical behavior developed in aqueous solution. Three elements of structural characterization are mainly described in the literature: the degree of galactose substitution, chain length, and galactose units distribution. This review article will attempt to highlight the impact of different structural features on physical properties such as solubility, viscosity, formation of hydrogels or gels in combination with other saccharides. The impact of industrial purification process on the structure and physical properties is also developed.     

黄原胶发酵生产工艺研究

本文研究} Xanthomonas Campestris XC-82. 5R5菌株的黄原胶最适发酵工艺条件.分析了不同碳源底物及溶氧水平对发醉过程的影响，确定了发酵最佳温度、初始pH值、菌龄，揭示了以菜油替代PPE作消泡剂的优点，同时认为不宜采用添加HZO:水的方式来改善发酵液的溶氧状况一实验表明，最佳摇瓶发酵工艺条件:蔗糖作碳源要优于葡萄糖，最适发醉温度’为28-32'C，接种菌龄为28hr，初始pH为7. 2;消泡剂为。.1%一。.2%菜油.     

新疆引种栽培杜仲和正品杜仲中微量元素含量比较研究

本文利用电感耦合等离子发射光谱仪分析了阿克苏栽培杜仲和正品杜仲中主要的微量元素,并比较了栽培杜仲和正品杜种中微量元素含量方面的差异。     

杜仲叶中绿原酸的协同增敏荧光光谱法测定

研究了四硼酸钠-阳离子表面活性剂十六烷基三甲基溴化铵(CTMAB)微乳液混合体系对绿原酸的协同荧光增敏作用.结果表明,单独存在的四硼酸钠和CTMAB对绿原酸的荧光强度无显著增敏作用,但四硼酸钠-CTMAB混合体系对绿原酸具有较好的协同荧光强度增敏作用.在优化条件下,绿原酸浓度在0.13～1.32μg·mL<-1>范围内...     

Polyelectrolyte complex materials consisting of antibacterial and cell-supporting layers

The characterization of a polyelectrolyte complex material comprised of two biopolymers, a chitosan upper layer and a gellan gum under layer, is reported. It is shown that the upper layer of chitosan with incorporated levofloxacin displays an antibacterial activity, while the under layer of a gellan gum/TiO(2) composite supports the growth of fibroblastic cells.     

Fabrication and Properties of Carbon Nanotube and Poly(vinyl alcohol) Composites

Dispersion of carbon nanotubes in a polymer matrix is one of the most critical issues in carbon nanotube/polymer composites. In this paper we discuss the considerable improvement in the dispersion of multiwalled carbon nanotubes (MWNTs) in poly(vinyl alcohol) (PVA) matrix that was attained through gum arabic treatment. The mechanical properties of these MWNT/PVA composites show that only 2 wt% nanotube loading increases the tensile modulus by more than 130%.     

Influence of molecular relaxation processes on mechanical properties of polyvinyl chloride in tensile experiments

The relation between the molecular relaxation processes and the results of tensile experiments has been studied for hard and toughened polyvinyl chloride (PVC). The relaxation spectra have been determined between 10^?4 and 10⁺⁴ sec by means of stress relaxation, flexural vibration experiments, and tensile tests. Yield stress, yield strain, rupture stress, rupture strain, and rupture energy have been determined at 23° and 50° C as functions of yield time or rupture time, respectively, over a time-range from 10^?2 to 10⁺⁴ sec approximately. It is shown that the molecular relaxation processes observed in the range of small deformations also influence the behavior in the nonlinear range, especially the elongation at rupture in tensile experiments. In addition, effects of the molecular processes on the yield stress, the rupture stress, and, consequently, the rupture energy have been observed. These effects are due to the time- and temperature-dependent decrease of the macroscopic stress and of the microscopic notch stresses by certain relaxation mechanisms. The most suitable characteristic parameters in tensile experiments are the yield stress and the rupture strain. It is pointed out that the usefulness of a single value of a mechanical property as determined in a standard “one-point” test is very restricted.