一步法络合型催化剂丙烯聚合反应动力学

<正> 丙烯聚合络合催化剂一般是由钛的氯化物和有机铝化合物及给电子体组成。Solvay型络合催化剂是用所谓三步法合成。我们采用烷基铝-醚络合物还原Ticl_4的一步法合成催化剂,不仅制备步骤简单,而且其性能也有所不同。三步法络合催化剂丙烯聚合动力学研究国内外已有报道。本文报道一步法络合催化剂的丙烯聚合动力学、聚合速率     

丁二烯在NdCl_3·2Phen-HAl(i-Bu)_2催化体系下的聚合动力学

氯化稀土的某些配合物与烷基铝组成的双烯烃定向聚合催化剂用于丁二烯聚合时,大多得到分子量较高的产物。最近我们报道了可在较宽范围内改变聚丁二烯分子量的三氯化钕邻菲啰啉配合物(NdCl_3·2Phen)与氢化二异丁基铝[HAl(i-Bu)_2]所组成的新的二元氯化稀土定向聚合催化剂。本文报导该体系下的丁二烯聚合动力学,测定了聚合反应速率对     

丙烯聚合用TiCl_4/MgCl_2催化剂的研究——聚合温度和烷基铝的影响

研究了不同助催化剂和不同聚合温度对催化剂TiCl4/MgCl2/9,9-双(甲氧基甲基)芴(BMMF)丙烯聚合性能的影响.研究结果发现该催化剂在高温(100℃)聚合时,采用还原能力和络合能力较弱的烷基铝(Hex3Al)为助催化剂可以得到高的立构选择性(97%)和高活性.100℃聚合时不同的助催化剂对催化剂得到的聚丙烯结构有重要影响.助催化剂为Me3Al聚合得到的中等等规聚丙烯含量比其他烷基铝高.助催化剂为Et3Al聚合得到聚丙烯链结构中含有少量乙烯共聚单元;而助催化剂为Me3Al,iBu3Al和Hex3Al聚合得到聚丙烯链结构中没有发现共聚单元.     

稀土定向聚合络合催化剂的研究

定向聚合所用的络合催化剂,过去只限于元素周期表中带有d电子的Ⅳ—Ⅷ族过渡金属元素。经过多年的探索研究,我们发现了新的一类定向聚合稀土络合催化剂。稀土络合催化剂在双烯烃的均聚和共聚中具有相当高的催化活性,特别良好的定向效应,所得聚丁二烯、聚异戊二烯及其共聚物的顺-1,4结构的含量达94％以上,并且性能优良。本文叙述了稀土络合催化剂的组成,稀土元素、烷基铝和第三组分等的变化对稀土络合催化剂的活性和定向性的影响,以及稀土络合催化聚合的某些机理。     

聚合温度对负载型Ziegler-Natta催化剂催化丁二烯-异戊二烯共聚合的影响

非均相TiCl₄/MgCl₂-AlR₃型Ziegler-Natta(非均相Z-N)催化剂是聚烯烃工业最重要的催化剂,经烷基铝活化的非均相Z-N催化剂具有复杂的活性中心结构,改变聚合温度、聚合时间、烷基铝种类及浓度等均会影响活性中心结构与催化性能.本文研究了不同聚合温度下TiCl₄/MgCl₂-AlEt₃(三乙基铝)催化丁二烯(Bd)和异戊二烯(Ip)的共聚合动力学,研究发现,随着聚合时间的延长,聚合活性先升高然后降低,在50℃聚合活性最高.采用核磁共振波谱(¹H NMR)、紫外荧光定硫仪和凝胶渗透色谱(GPC)研究了共聚物的微观结构、活性中心数和分子量及其分布,发现随着聚合时间的延长及聚合温度的升高,活性中心数、共聚物中反式-1,4-结构、分子量及分子量分布均发生不同规律的变化.本文研究结果可为进一步理解非均相Z-N催化剂在不同聚合温度下催化共轭二烯烃聚合的动力学及其关键影响因素提供参考.     

烷基铝对球形MgCl_2负载的茂金属催化剂催化乙烯聚合的影响

以甲基铝氧烷(MAO)为助催化剂的茂金属催化剂虽然具有催化活性高、分子量分布窄、聚合物化学组成均匀等优点,但其极高的Al/Zr比和聚合物颗粒形态差等缺点限制了其工业化应用,因此对茂金属催化剂的负载化成为近年来的研究热点.在众多的载体中,球形MgCl2是研究得很少的一类载体,文献中曾采用先负载主催化剂茂金属配合物,聚合时再加入助催化剂MAO的方法[1],由于加入的MAO与主催化剂的络合能力很强,会使部分载上的主催化剂溶解下来,成为均相聚合[2,3],导致聚合物颗粒形态差,且粘釜现象严重.我们则采用相反的思路,即先将助催化剂MAO负载在球形MgCl2上,制得MgCl2/MAO,在聚合前再将MgCl2/MAO与Et[Ind]2ZrCl2混合陈化,并立即在少量烷基铝活化下引发乙烯聚合[4],实验结果表明,该催化剂聚合活性高、聚合物的颗粒形态好、且不粘釜,是一种新型的载体催化剂.由于烷基铝的加入可使催化剂的活性大幅度提高,所以本文将烷基铝也称作助催化剂,来研究其对该载体催化剂催化乙烯聚合的影响.     

稀土配位催化合成聚乳酸

本文开发了合成聚乳的一类新型催化剂, 它是由稀土化合物-三烷基铝-水组的配位催化剂。试验表明稀土配位催化剂可以使丙交酯在甲苯溶液中以高转化率聚合, 得到分子量可控的聚乳酸。并研究了稀土元素种类、不同配位基团及聚合条件变化对丙交酯开环聚合的影响。     

丙烯聚合用TiCl_4/MgCl_2催化剂的研究——内给电子体的作用

采用相同制备工艺 ,制备分别以邻苯二甲酸二异丁酯 (DIBP)和 9,9 双 (甲氧基甲基 )芴 (BMMF)为内给电子体和不加入内给电子体 3种催化剂 .研究了它们在无外给电子体时聚合性能 ,以及合成的聚丙烯的等规度 ,分子量及其分布 .并采用CRYSTAF和1 3C NMR对聚丙烯沸腾庚烷不溶部分结晶性能和序列结构进行分析 ,结果表明内给电子体对聚丙烯分子链序列结构有很大影响 ;BMMF催化剂、DIBP催化剂和无内给电子体催化剂合成的聚丙烯规整性依次下降 .对BMMF催化剂 ,当烷基铝为Et3Al时 ,铝钛比增加 ,等规度和活性明显下降 .当烷基铝i Bu3Al时 ,铝钛比增加 ,等规度略微下降而活性增加 ;但是1 3C NMR研究发现其 (铝钛比为 3 0 0时 )庚烷不溶物的规整性与DIBP催化剂的庚烷不溶物的规整性一致 .这表明内给电子体在聚合中的作用不在于是酯还是醚 ,在于它与氯化镁的络合强度 .络合越强 ,得到的聚丙烯分子链越规整     

不同结构烷基铝催化异戊二烯齐聚与聚合行为研究

烷基铝（AlR₃）作为Ziegler-Natta催化剂体系的助催化剂组分,起到烷基化、还原主金属化合物、参与活性中心形成与演变、链转移剂等重要作用.然而烷基铝自身对二烯烃单体也具有催化作用.本工作采用不同结构烷基铝如三乙基铝（AlEt₃）、三异丁基铝（Al（i-Bu）₃）、氢化二异丁基铝（AlH（i-Bu）₂）、一氯二乙基铝（AlEt₂Cl）、二氯一乙基铝（AlEtCl₂）,研究了烷基铝的种类和浓度对异戊二烯催化行为的影响.采用核磁共振氢谱（¹H NMR）、凝胶渗透色谱（GPC）、气相色谱-质谱联用（GC-MS）等对产物的微观结构（顺式-1,4-和反式-1,4-含量）和分子量及分布等进行了表征,探讨了不同结构烷基铝的催化行为.发现烷基铝不仅可以催化异戊二烯齐聚,与微量水作用后还可以引发异戊二烯阳离子聚合,得到顺反混合结构的线性聚合物.烷基铝浓度对其催化行为有较大影响.当n（Al）/n（M）=1050×10^-5时,AlEtCl₂的催化活性显著提高,产物主要为线性聚合物;而其他结构烷基铝的催化活性较低.当n（Al）/n（M）≤350×10^-5,烷基铝自身催化异戊二烯齐聚及聚合能力极弱.过低和过高的烷基铝浓度都不利于获得高分子量聚合物.这为深入理解Ziegler-Natta催化剂体系烷基铝组分的催化作用及其对聚合物的影响提供依据.     

丁二烯在某些钕催化剂体系中聚合活性中心数的测定和动力学的研究Ⅱ.聚合链增长、链转移及链终止过程的研究

本文应用氚醇淬灭法和动力学方法研究了丁二烯在钕化合物-烷基铝催化体系中的聚合动力学.结果表明,聚合速度与单体浓度和活性中心浓度的一次方成正比.对烷基铝的链转移反应进行了研究,测定了用几种不同的钕化合物和烷基铝所组成的催化剂时的链转移速度.链终止反应速度与活性中心浓度的二次方成正比.计算了在不同聚合条件和各种催化剂组成时的链增长、对烷基铝链转移及链终止反应的速度常数.     

THE BIMODAL MOLECULAR WEIGHT DISTRIBUTION OF cis-POLYBUTADIENE POLYMERIZED WITH LANTHANIDE COMPLEX CATALYSTS

The variation of the molecular weight and molecular weight distribution of cis-polybutadiene in the course of polymerization catalyzed by lanthanide complex composed of triisobutyl aluminium or diisobutyl aluminium hydride was investigated by osmometry, viscometry and size exclusion chromatography. By analyzing the experimental data, the reasons of the appearance of himodal molecular weight distribution were elucidated and the possible mechanisms of polymerization were discussed.     

稀土催化聚合的顺式聚丁二烯的单分散粘度方程

对十一个未经分级的多分散稀土顺丁橡胶试样作了渗透压和粘度的测量,计算得到的数均分子量_n及特性粘数[<η>]列于表中。     

The effect of the nature of organoaluminium compound and the catalytic system preparation procedure on molecular characteristics of 1,4-Cis-polybutadiene

This study investigated the effect produced by the preparation procedure of a 2-component lanthanide catalytic system and by the nature of organoaluminium compound on 1) the molecular characteristics of 1,4-cis-polybutadiene (PB), 2) the regularities of its average molecular weight (MW), and 3) molecular weight distribution (MWD). The kinetic parameters of the polymerization process were calculated. The principal regularities of variations in PB molecular characteristics with respect to the polymerization conditions, i.e., OAC and monomer concentrations and temperature, are retained with different procedures of the lanthanide catalytic system, and those present distinctive features of the catalytic complexes studied in this article. But as for differences in MW and its patterns of dependence on monomer conversion rate and OAC nature, these are due to changes in kinetic parameters of the polymerization, which occur with the use of the catalyst prepared by a different procedure. © 1994 John Wiley & Sons, Inc.     

含反式-1,4和间规-1,2链节的聚丁二烯X-射线衍射谱分析

<正> 近年来陆续出现在顺式-1,4聚丁二烯分子链中引入室温下可结晶的反式-1,4及间规-1,2聚丁二烯链节,以期改善顺丁橡胶的抗撕裂性和抗弯曲性等。有关这方面的结构表征工作尚很少报道。本工作用广角X-射线衍射(WAXD)方法,对钒、钴催化体系合成的含反式-1,4及钴催化体系合成的含间规-1,2的顺丁橡胶进行了结构表征。     

Sol‐Gel Preparation and Characterization of Codoped Yttrium Aluminium Garnet Powders

A sol‐gel method has been developed to prepare lanthanide‐codoped yttrium aluminium garnet (Y₃Al₅O₁₂, YAG) ceramic samples. The XRD patterns of the polycrystalline Y₃Al₅O₁₂:Nd,Ho and Y₃Al₅O₁₂:Nd,Er powders sintered at 1000 °C showed the formation of monophasic garnet materials. A homogeneous distribution of rare‐earth dopants in the YAG lattice was achieved in both cases. The morphological characterization of lanthanide‐codoped YAG by scanning electron microscopy (SEM) showed the formation of highly agglomerated nanocrystalline samples. The luminescence properties of sol‐gel derived doubly activated yttrium aluminium garnet samples were also investigated in the present study.     

Narrow band thermoluminescence of auer mantles containing neodymium,holmium, erbium or thulium in mixed oxides

The emission spectra of the mixed oxides (zirconium and thorium oxides, sesquioxides and lanthanide aluminium or gallium perovskites) correspond mainly to hypersensitive pseudoquadrupolar transitions in the partly filled 4f shell of trivalent lanthanides. The influence of quadrivalent cerium, praseodymium and terbium is discussed.     

Separation of some burn-up monitors from the UO2−Al nuclear fuel

The separation of caesium, cerium, neodymium, europium and uranium from the UO₂?Al fuel samples has been studied. Experiments were carried out with unirradiated and irradiated fuel samples. The dissolved samples contained a large excess of aluminium with respect to uranium (the molar ratio Al∶U was ～17∶1). The presence of aluminium particularly disturbed the chromatographic separation of the lanthanide burn-up monitors. The latter were separated from uranium and aluminium and from one another using the precipitation method with a cerium carrier, followed by extraction with HDEHP and a column separation with the same extractant. Aluminium and uranium first were determined together as precipitates with 8-hydroxychinoline, and then the uranium contribution was independently assayed potentiometrically with a K₂Cr₂O₇ solution.     

镍催化体系合成顺式聚丁二烯的研究——Ⅴ.探讨活性中心上镍的价态

本文用ESR方法结合聚合实验,说明镍催化体系在合成顺式聚丁二烯上的活性中心是Ni~0和Ni~+,并且二者在反应中是共存的。     

Polyethylene with bimodal molecular weight distribution synthesized by 2,6-bis(imino)pyridyl complexes of Fe(II) activated with various activators

Polyethylenes with bimodal molecular weight distribution (MWD) were synthesized by 2,6-bis(imino)pyridyl complexes of Fe(II) combined with different activators, which were prepared from alkylaluminium. It is found that the molecular weight (MW) and MWD was influenced by not only iron complexes but activators as well. The activator plays key important role in determination of the MW and MWD of final polymer and the MWD shape could be regulated by selection of various activators and polymerization conditions. The study on the variation of the MWD with the polymerization time and fitting of bimodal MWD with two Flory distributions suggests that bimodal MWD is caused by chain transfer reaction to activator or two active sites.     

ON THE ORIGIN OF STRESS PEAK IN UNI-AXIAL STRETCHING OF AMORPHOUS POLYMERS

Rubber of high molar mass, like cis-polybutadiene, shows a stress peak on theenineering stress-strain curve during stretching at room temperature. In this work cis-polybutadiene samples were swollen in a poor solvent, CHCl_3/EtOH (1/1 v/v), for differenttimes. It was found that both the initial modulus and the stress peak on stretching de-creased in magnitude with increasing swelling time and the peak disappeared entirely after1 hour of swelling. On further swelling the initial modulus increased somewhat and a smallstress peak re-appeared after swelling for 2 h. The disappearance of the stress peak afterswelling is interpreted as the result of disruption of cohesional entanglements present in theinitial rubber sample. The re-appearance of a small stress peak and the increase of modu-lus on further swelling are interpreted as being of the same nature as the phenomenon ofanti-plasticization. It is the result of forming some new cohesional entanglements of largerbinding energies through longer range chain segmental motions excited after the disruptionof the previously existing cohesional entanglements in the rubber. Thus an understand-ing of the stress peak on stretching a high molar mass rubber and the phenomenon ofanti-plasticization on molecular level has been put forward.