不同分子量聚丙烯腈的制备及其高压静电纺丝研究

采用DMSO/H2O混合溶剂法制备了5种不同分子量的PAN,并以PAN为原料,DMF为溶剂,配成纺丝溶液,通过高压静电纺丝技术制备超细纤维毡(UFFM)。研究表明,相同单体组成和浓度、相同反应条件情况下,通过聚合制备PAN,随着混合溶剂中水含量的增加,生成的PAN粘均分子量相应增加,其转化率也增加。聚合所得的不同分子量PAN的热重分析显示,随着PAN分子量的增加,热重曲线的剧烈失重区会越来越明显,剧烈失重区的失重率也呈增加的趋势;高压静电纺丝研究发现,PAN-4和PAN-5纺丝溶液由于分子量过高而不可纺;另外,研究还发现,较高的纺丝电压有利于纤维直径的减小,但相应的纺丝稳定性减小,导致纤维直径分布的离散度增加。     

高平均分子量聚丙烯腈的制备、性能和应用

介绍了高平均分子量聚丙烯腈的主要制备方法，如混合溶剂自由基聚合、水相悬浮聚合、反相浮液聚合、离子聚合、紫外光辐射聚合等。还根据高平均分子量聚丙烯腈的性能探讨了其在高性能碳纤维前驱体聚丙烯腈原丝和高强高模中空纤维过滤膜方面的应用。     

引发转移终止剂技术合成含有聚异戊二烯链段的三嵌段共聚物

含聚异戊二烯 (ＰＩＰ)链段的嵌段共聚物有着广泛的应用[1～ 3 ] ,有关它的合成、性能表征及应用方面的研究一直是学术及工业界的研究热点 .传统上 ,含有ＰＩＰ链段的嵌段共聚物用活性负离子聚合的方法来合成 ,例如 :聚苯乙烯 聚异戊二烯嵌段共聚物[3 ,4 ] .这是由聚合物增长链端的特殊活性所决定的 ,采用活性负离子聚合方法 ,不但能很好地控制共聚物的分子量和分子量分布 ,而且能控制共聚物中各组分的比例 .但是 ,负离子聚合通常需在较苛刻的条件下进行 ,如低温高真空、高纯度的单体和溶剂 ,而且能用于负离子聚合的单体也有限 .相对而言 ,…     

原子转移自由基聚合法合成聚丙烯腈的研究进展

聚丙烯腈纤维是一种具有优良的化学和物理性能的高分子材料,高分子量、高等规度的聚丙烯腈(PAN)是合成高性能聚丙烯腈纤维的必要要求,原子转移自由基聚合法(ATRP)可以预先确定相对分子量且分散系数低,操作简单、反应条件温和,被广泛应用于聚丙烯腈的合成。本文介绍了原子转移自由基聚合的基本原理及其合成聚丙烯腈的研究概况,探讨了不同溶剂对聚合速率的影响、不同种类过渡金属催化剂及相关配体在聚合反应中的应用、引发剂的选择及分类。     

丙烯腈-衣康酸基纳米纤维纱线的热稳定及碳化研究

碳纳米纤维主要以聚丙烯腈(PAN)作为前驱体,通过纺丝、热稳定、碳化等后处理工艺制备而得.但是,PAN基纳米纤维取向度低、致密性差,热稳定后环化度低,碳化后导电性差等缺点阻碍其在高性能碳纳米纤维领域的发展.因此,在PAN分子链中引入衣康酸(IA),通过溶液聚合法合成了P(AN-co-IA)共聚物并通过静电纺丝法制备了P...     

丙烯腈-衣康酸基纳米纤维纱线的热稳定及碳化研究

碳纳米纤维主要以聚丙烯腈(PAN)作为前驱体,通过纺丝、热稳定、碳化等后处理工艺制备而得.但是,PAN基纳米纤维取向度低、致密性差,热稳定后环化度低,碳化后导电性差等缺点阻碍其在高性能碳纳米纤维领域的发展.因此,在PAN分子链中引入衣康酸(IA),通过溶液聚合法合成了P(AN-co-IA)共聚物并通过静电纺丝法制备了P...     

用双官能团引发剂进行的基团转移嵌段共聚研究

本文用二种双官能团引发剂进行基团转移嵌段共聚研究,得到了一系列实测分子量和理论分子量相近、分子量分布较窄的A-B-A型嵌段共聚物。用GPC、~1H-NMR、DSC等手段对嵌段共聚物进行了表征,证明确是两相嵌段共聚丙烯酸酯。发现位阻较大的单体作为第二单体时不利于聚合。过高的催化剂用量使嵌段共聚的总转化率降低。使用极性较大的溶剂可缩短第一步聚合的诱导期,但不影响第二步聚合的诱导期,即极性较大的溶剂有利于催化剂的离解。单体浓度增大使共聚物的分子量减小,多分散性指数增大。可通过单体投料比改变共聚物的热形变温度。     

用于大分子定向自组装的新型嵌段共聚物的合成与表征

设计了具有高Flory-Huggins相互作用参数的嵌段共聚物聚(对叔丁基苯乙烯)-b-聚(甲基丙烯酸羟乙酯)(PtBS-b-PHEMA),并分别采用阴离子聚合和原子转移自由基聚合(ATRP)方式制备了不同嵌段比例、不同分子量的窄分子量分布的该嵌段共聚物。利用核磁共振分析了嵌段共聚物的组分,利用小角X射线散射(SAXS)分析了嵌段共聚物相分离后的尺寸及结构,对比研究了两种聚合方式对嵌段共聚物性能的影响。结果表明,采用阴离子聚合方式得到的嵌段共聚物分子量分布更窄,相同分子量下发生微相分离的尺寸更小,其在150℃真空烘箱中加热18h后可以形成尺寸为9.96nm的柱状相及8.42nm的层状相。     

自由基技术在α-烯烃均聚以及与功能性单体共聚中的应用进展

综述了自由基聚合在α-烯烃均聚及与功能性单体共聚制备功能化聚烯烃方面的研究进展。自由基聚合方法具有易操作、成本低等优点,特别是随着活性自由基聚合的发展,使对通过自由基聚合所得聚合物的结构进行精确调控成为可能。目前在α-烯烃均聚方面,通过选择适当的溶剂以及添加有机锂盐,使在相对温和条件下自由基引发α-烯烃合成高分子量聚合物成为可能。在共聚体系中,路易斯酸或布伦特斯酸的引入可以大幅提高共聚物中α-烯烃的含量。     

聚合反应介质对丙烯腈/衣康酸共聚物结构与性能的影响

利用混合溶剂沉淀聚合法研究了水/环丁砜(H_2O/TMS)等4种不同聚合反应介质对丙烯腈/衣康酸(AN/IA)共聚物的转化率、重均分子量(Mw)及分布(D)、表面微观形貌、竞聚率及链结构、聚合物热性能和纺丝性能的影响.结果表明,P(AN/IA)聚合物转化率随着混合溶剂中H_2O含量的增加,呈先升高后降低的趋势.P(AN/IA)的Mw与水/溶剂比例成线性增加的关系,其中,以H_2O/TMS作为混合反应介质所制备P(AN/IA)的Mw最大,D最小(小于2).AN与IA以H_2O/TMS为聚合介质时倾向于理想共聚,2IA链段分布几率仅为2.87%.以H_2O/TMS为聚合体系所制备P(AN/IA)结构疏松、颗粒粒径较小且易溶解,预氧化时环化反应放热速率低、放热区间宽,热稳定化阶段形成耐热梯形结构反应所需能垒小.P(AN/IA)/TMS纺丝溶液的表观黏度低,TMS为PAN的良溶剂.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.