Multi-arm star-branched polyisobutylene ionomers

A series of multi-arm star-branched polyisobutylenes was synthesized via living carbocationic polymerization. Arms with molecular weights ranging from 10,000 to 30,000 g/mol were prepared using the cumyl chloride/TiCl₄/pyridine initiation system in 60/40 (v/v) hexane/methyl chloride at − 80 °C and linked by sequential addition of divinylbenzene. The weight average number of arms per star polymer, N _w, scaled inversely with arm molecular weight and ranged from 32 to 5. Star-telechelic ionomers were produced by sulfonation of the aromatic initiator residue at the end of each arm, followed by neutralization. Sulfonation was quantitative as indicated by acid-base titration. Potassium ionomers were elastic solids which were marginally soluble in THF; the precursors were tacky and freely soluble in THF. Ionic modification did not alter the glass transition temperature (− 66 °C), but the thermal decomposition temperature in N₂ was increased from 375 to 400 °C. Received: 25 July 1997/Accepted: 27 August 1997     

Surface tensions of liquid polyisobutylenes

Measurements of surface tensions were carried out in the temperature range 25–120°C on seven different liquid polyisobutylenes with molecular weights ranging from 100 to 80,000. Relationships between the surface tenstion of polyisobutylene and other properties, such as the parachor, cohesive-energy density, and molecular weight are discussed.     

Synthesis and characterization of aldehyde-capped polyisobutylenes

Summary The synthesis and characterization of linear mono- and ditelechelic polyisobutylenes (PIBs) carrying terminal primary aldehyde groups are described. The synthesis starts by chlorine terminated PIBs (PIB−Cl and Cl−PIB−Cl) prepared by inifering or living carbocationic polymerization. These starting materials were dehydrochlorinated to vinylidene (∼CH₂−C(CH₃)=CH₂) terminated PIBs and hydroformylated with CO/H₂ in the presence of a rhodium catalyst. According to NMR (500 MHz) and GPC analyses, the transformations are selective and demonstrably quantitative. The structures of these novel polymers are: I view of the rich chemistry of the aldehyde group, these materials are valuable intermediates.     

超重力法制备高活性聚异丁烯工艺研究

将超重力技术与阳离子聚合技术有机结合,首次在旋转填充床(RPB)中制备了高活性聚异丁烯(HRPIB)产品,考察了旋转床转速、单体与催化剂流量比、单体浓度等操作条件对聚合反应单体转化率和聚异丁烯数均分子质量、分子质量分布、末端α-双键摩尔分数的影响规律。结果表明,通过调节操作条件,可以实现高活性聚异丁烯的可控生产。制备的聚异丁烯产品数均分子质量1 600~3 400 g/mol,分子质量分布为2.2~3.0,末端α-烯烃摩尔分数在85%左右,单程转化率最高可以达到84%,聚异丁烯产品的各项指标略优于传统工艺。该工艺使物料在反应器内的平均停留时间从传统工艺的20~300 min缩短至小于1 s,反应器的体积大大缩小,生产效率大幅度提高。     

Synthesis of functionalized polyisobutylenes on mono- and bifunctional catalytic systems

The possibility of synthesizing functionalized polyisobutylenes on mono- and bifunctional initiators in the presence of aluminum-containing Lewis acids was demonstrated. It was shown that addition of electron-acceptor solvating additives or sterically hindered electron donors, as well as the method of microdelivery of the monomer to the polymerization system decrease the probability of chain transfer reactions with the formation of a dead polymer.Moscow Institute of Precision Chemical Technology. Translated from Khimicheskie Volokna, No. 6, pp. 18–20, November–December, 1993.     

Influence of molecular weight on the creep behavior of undiluted polyisobutylenes

The elongational behavior in constant force experiments has been considered for three samples of commercial polyisobutylene. The results compare favorably with the predictions of two existing non-linear theories as long as the samples deform homogeneously. Some qualitative observations have been made with reference to the “failure point”, i.e., the point where a non-homogeneous deformation begins.     

Efficient Adaptive Randomization and Stopping Rules in Multi-arm Clinical Trials for Testing a New Treatment

Abstract

Motivated by applications to confirmatory clinical trials for testing a new treatment against a placebo or active control when the new treatment has k possible treatment strategies (arms)—for example, k possible doses for a new drug—we develop an asymptotic theory for efficient outcome-adaptive randomization schemes and optimal stopping rules. Our approach consists of developing asymptotic lower bounds for the expected sample sizes from the k treatment arms and the control arm and using generalized sequential likelihood ratio procedures to achieve these bounds. Implementation details of our design and analysis and comparative simulation studies are also provided.     

星形聚合物的发展近况

综述了采用负离子聚合技术合成的星形聚合物的结构与性能的关系、合成路线及应用。新开发的星形聚合物,如ＳＳＢＲ,ＬＣＢＲ,ＭＶＢＲ,ＨＶＢＲ,ＳＩＢＲ等,运用高分子分子设计的方法来合成,因而具有更佳的综合性能,如高的抗湿滑性及低的滚动阻力等。     

星形聚合物的研究与应用进展

回顾了结构性能独特且应用颇为广泛的非线性星形聚合物研究现状;介绍了星形聚合物的特点、应用,以及通过活性聚合制备星形聚合物的不同合成方法,比较了各种合成方法的优缺点;综述了星形聚合物用作研究聚合物的支化模型、简化树形聚合物复杂的支化结构、获得聚合物支化信息的研究进展。     

A cost-effective process for highly reactive polyisobutylenes via cationic polymerization coinitiated by AlCl3

The initiating system consisting of AlCl₃ with dialkyl ether such as di-n-butyl ether or diisopropyl ether has been successfully developed for providing a cost-effective process of synthesis of highly reactive polyisobutylenes (HRPIBs) with large proportion of exo-olefin end groups up to 93 mol% at temperatures ranging from −20 to +20 °C. The above dialkyl ethers played very important roles in promoting the directly rapid β-proton elimination from -CH₃ of the growing chain ends to create exo-olefin end groups and decreasing or even suppressing the carbenium ion rearrangements to form the double bond isomers. Very importantly, the highly reactive PIBs with 80-92 mol% of exo-olefin end groups, having low M_ns of 1300-2300 g mol⁻¹ and monomodal molecular weight distribution (M_w/M_n = 1.7-2.0) could be achieved at 0-20 °C. These results are comparable to those of commercial HRPIBs produced industrially by the best BF₃-based initiating system at far below 0 °C.     

星形聚合物的最新研究进展

星形聚合物作为一种非线性聚合物,具有广阔的理论研究意义和工业应用前景,其结构、形态、合成与功能都是高分子科学领域中的热点问题。本文主要综述了均臂星形聚合物、杂臂星形聚合物、树状或支化结构星形聚合物的最新研究进展。     

多臂星形聚乙二醇的合成

聚乙二醇(PEG)经与丁二酸酐发生酯化后,在两末端引入羧基,再与氯化亚砜反应得到聚乙二醇二酰氯,此产物再分别与丙三醇、季戊四醇或D-山梨醇等多元醇反应,可分别得到三臂、四臂和六臂星形PEG。用傅里叶变换红外光谱和核磁共振氢谱等对各产物进行了表征,端基分析法得到三臂、四臂和六臂PEG的数均分子量平均值分别为3 794,4 738,6 432,表明采用上述合成路线可成功得到末端为羧基的多臂星形PEG。     

中国陶瓷机械业的又一颗新星

广东佛山新景泰陶瓷机械有限公司在陶瓷行业的激烈竞争中,逐渐脱颖而出成为陶瓷机械行业内一颗求实、创新的新星,受到国内外陶瓷业界人士的格外关注,这完全得益于新景泰人善于在产品创新及营销上做出差异化发展的文章.     

星形聚合物微凝胶的合成及其研究进展

星形微凝胶是1种具有特殊结构的聚合物微凝胶,具有广阔的应用前景。活性聚合(如阴离子活性聚合、阳离子活性聚合、氮氧稳定自由基聚合及原子转移自由基聚合(ATRP))是星形微凝胶合成的最常用且最有效的方法。对该方法在星形微凝胶合成方面的应用及其研究进展进行了综述。     

星型抗氧剂的合成与表征

将3,5-甲酯制成3,5-丙酰氯,接枝到树状大分子聚酰胺-胺(PAMAM)骨架上,得粗产品,并对粗品的精制工艺进行了探索。讨论了乙醇和水用量对产品质量及收率的影响,最佳处理条件为:2 g粗产品用25 mL乙醇溶解,用120 mL水析出。并对除酸剂进行了筛选,得出环己烷为最佳除酸剂。红外光谱和元素分析表明,合成的分子结构与目标设计的分子结构基本相符。对合成的星型抗氧剂进行了抗氧化性能评价,以PP(T30S)作为基体,以抗氧剂3114作为对比参照物,测试了氧化诱导期(OIT),测试结果表明,星型树状酚类抗氧剂具有抗氧化性能,且其抗氧化性能优于抗氧剂3114。     

Rheology of core cross-linked star polymers

The rheological characterization for a set of structurally diverse core cross-linked star (CCS) polymers is presented. The influence of arm molecular weight (M_w(arm)) and CCS polymer molecular weight (M_w(CCSP)) on the steady- and dynamic-shear properties determined by plate rheometry will be discussed. Both these parameters dramatically affect the CCS polymer solution properties and determine its “molecular softness”; a key feature of star polymers. Data from light scattering and capillary viscometry analysis are also presented to relate the dimensional configuration of the CCS polymers to their rheological properties. The methodology for tuning the structure of the CCS polymer is provided and the implications on solution properties are discussed.