Crystallization behavior of blends of high-density polyethylene with novel linear low-density polyethylene

Blends of high-density polyethylene (HDPE) with novel linear low-density polyethylene (LLDPE) samples in the whole range of compositions were investigated by means of differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The LLDPEs are ethylene/octene-1 copolymers prepared with a single-site catalyst, with a narrower distribution of branches compared to Ziegler-Natta type polymers. It was found that cocrystallization or separate crystallization in the blends profoundly depends on the content of branches in the LLDPE, while the critical branch content of the novel LLDPE for separate crystallization is much lower than that of commercial LLDPE (prepared with Ziegler-Natta catalysts). This implies that the miscibility of linear and branched polyethylene is also affected by the distribution of branches. The marked expansion of the unit cell in cocrystals, which are formed by HDPE with the novel LLDPE, indicates that the branches are included in the crystal lattice during the cocrystallization process. The result is very helpful to understand the phenomenon that the unit cell dimensions of commercial branched polyethylene are larger than those of linear polyethylene.

TiCl_4／SiO_2－MgCl_2载体催化剂下的乙烯／己烯－1共聚反应

ＴｉＣｌ_４／ＳｉＯ_２－ＭｇＣｌ_２载体催化剂下的乙烯／己烯－１共聚反应陈辉，张学全，黄葆同王展望，杨永然（中国科学院长春应用化学研究所长春１３００２２）（辽阳化纤公司化工三厂辽阳）关键词乙烯，己烯，共聚，Ｚｉｅｇｌｅｒ－Ｎａｔｔａ催化剂乙烯／α－烯?..

不对称取代钛茂/甲基铝氧烷催化体系丙烯聚合立构控制

利用一种新合成途径制备了单取代钛茂化合物(η~5-环戊二烯)[η~5-(1-(4-甲氧基苯基)环已烯基)环戊二烯]二氯化钛(Ⅰ),以衍射法确定其晶体结构属正交晶系,空间群P2_12_12_1,晶胞参数a=0.9680(5)nm,b=1.2846(5)nm,c=1.6944(6)nm,Z=4,R=0.066.详尽考察了不同聚合温度条件下Ⅰ/甲基铝氧烷(MAO)催化体系对丙烯聚合的立体化学控制,发现随着聚合温度的变化,能够生成等规、无规、间规三种不同立构取向的聚丙烯;其中等规、间规聚丙烯是由对映结构活性中心及链末端共同控制生成,而无规聚丙烯则受Bernoullian生成方式控制.

Nd-Al双金属活性体对异戊二烯的溶液聚合

近年来,对于稀土Ziegler-Natta催化剂活性体的研究比较活跃。使用催化剂活性体可以消除剩余烷基铝等因素对聚合反应的影响,比以前所用的多组分混合物的催化体系更客观地反映出聚合过程。我们在以前工作的基础上,从体系中分离出Nd-Al双金属活性体,并用于引发异戊二烯溶液聚合,探讨不同聚合条件下异戊二烯溶液聚合的规律,以利于对稀土催化聚合反应的深入了解。

Nd-Al双金属活性体的组成及其对共轭双烯烃的聚合

稀土Ziegler-Natta催化剂活性体对双烯烃配位聚合的研究已有很多报道。作者曾从NdCl_3·3P_(350)~(**)-Al(i-Bu)_3体系分离出Nd-Al双金属活性体。本文从NdCl_3·3P_(350)-HAl(i-Bu)_2和Al(C_2H_5)_3反应体系中分离出一系列Nd-Al双金属活性体,用元素分析方法研究了这些活性体的组成,并综合考察了在无助催化剂AlR_3存在下从不同烷基铝获得的活性体本身对共轭双烯烃的定向聚合能力。 单体、溶剂、HAl(i-Bu)_2、Al(C_2H_5)_5及活性体的合成,聚合方法,聚合物表征均按文献[4]。

NdCl_3·3P350-AlR_3二元催化体系对双烯烃的定向聚合

由氯化稀土的不同种类磷酸酯配合物与三烷基铝组成的Ziegler-Natta催化剂对双烯烃聚合的研究已有报道,其中聚合活性最高的NdCl_3·3P350—AlR_3二元催化体系对丁二烯溶液聚合及异戊二烯本体聚合的详细研究尚未见报道,本文考察了该体系对双烯烃的定向聚合能力,通过二元体系与相应的催化剂活性体聚合规律的对比,提高对稀土催化聚合反应过程的认识。

一种均相稀土催化剂反应过程的初步研究

稀土元素组成的Ziegler-Natta型催化剂,其相态常受体系中Cl/Nd克原子比所制约,仅在Cl/Nd≤2克原子比时呈均相态。最近发现一类新型催化体系,可在较宽Cl/Nd下保持均相态,如以Me_2SiCl_2(二甲基二氯硅烷),烯丙基氯等为第三组份所组成的体系。

多核Nd-Al双金属配合物对丁二烯的聚合——Ⅱ.聚合的一般规律

在从均相稀土Ziegler-Natta催化剂中分离出有双烯聚合活性的Nd-Al双金属配合物的基础上,利用该配合物可在无助催化剂烷基铝存在下单独引发丁二烯聚合的特性,详细研究了活性体、外加烷基铝、单体浓度,温度及时间等变量对聚合的影响;对比了活性体引发聚合与一般Ziegler-Natta催化聚合在一般规律上的异同。以更客观的实验事实论证了烷基铝在聚合过程中的作用,通过聚合产物的GPC测定讨论了活性体聚合中存在的键转移反应,确认外加烷基铝的键转移能力最强。所得结果有助于对稀土催化定向聚合过程的深入了解。

稀土-其它过渡金属混合催化剂用于共轭双烯烃的聚合——Ⅱ烷基铝对丁二烯聚合及产物微观结构的影响

某些过渡金属组成的Ziegler-Natta催化剂聚合共轭双烯烃,所得聚合物的微观结构易随聚合条件和主催化剂配体的改变而异.具有d电子的钴、钛催化体系聚合丁二烯,既可得cis-1,4结构聚丁二烯,又可得1,2结构的聚丁二烯;而具有f电子的稀土催化剂聚合共轭双烯烃,无论怎样改变其聚合条件和配体,一般皆得高顺式聚合物.一般认为:这种定向性的特征是由单体向活性中心上配位、插入时的环境及活性中心的本质所决定的.在第一报中作者利用同一种配位体,使具有d电子的过渡金属Fe和具有f电子的稀土

Isospecific polymerization of styrene with modified ziegler-type catalysts

Effects of various kinds of additives as well as aging of the catalyst on the polymerization of styrene catalyzed by TiCl4/MgCl2-AlEt3 system have been studied. Experiments show that in toluene the isotacticity of polystyrene can be up to 83% for aged catalyst, whereas when the catalyst is not aged. non-stereospecific polymer is the main product. When PCl3 is used as an additive, the catalyst system gives high activity and isotacticity. The use of a mixture of AlEt3/H2O (1: 1 mole ratio) as a cocatalyst is also efficient. The catalyst [TiCl4-PCl3/MgCl2-AlEt3/H2O] displays high activity and product isotacticity (94%) with an average molecular weight up to 2 X 10(-6). When Co(acac)(3) is added to to [TiCl4/MgCl2-AlEt3] catalyst after it was aged, the isotacticity can be up to 97%. (C) 2001 Elsevier Science Ltd. All rights reserved.

Kinetic and Size Control of Polystyrene and Polyacrylic Octadecyl Ester Lattices Via Polymerization in O/W Microemulsions

The kinetic studies of the acrylic octadecyl ester and styrene polymerization in microemulsion systems, (1) cetyl pyridine bromide (CPDB)/t-butanol/styrene/water; (2) CPDB/t-butanol/toluene + acrylic octadecyl ester (1:1, w/v)/ water; (3) cetyl pyridine bromide/styrene/formamide, were made by using dynamic laser light scattering techniques (DLS). The mechanisms of nucleation of latex particles were discussed. The most possible nucleation location of the styrene and acrylic octadecyl ester microlatex particles in aqueous microemulsion system is in aqueous phase via homogeneous nucleation. Meanwhile, parts of microlatex particles are possibly produced via swollen micelles (microemulsions) and monomer droplets nucleation. On the other hand, the most possible nucleation location of the styrene microlatex particles in nonaqueous microemulsion system is inside monomer droplets. The relationship between the amount of monomer and the size of microlatex was also investigated. It has been found that the size of microlatex particles could be controlled by changing the amount of monomer. (C) 2002 Elsevier Science B.V. All rights reserved.

Preparation of pH-sensitive polymer by thermal initiation polymerization and its application in fluorescence immunoassay

A fluorescence immunoassay for human IgG (Ag) was developed using a pH-sensitive polymer prepared by thermal initiation or redox initiation polymerization as a carrier. In the competitive immunoassay, appropriate quantity of Ag was immobilized on the polymer and the standard Ag (or sample) solution, and a constant amount of fluorescein isothiocyanate labeled goat anti-human IgG antibody (Ab-FITC) was added. Immobilized Ag and the standard (or sample) Ag competed for binding to the Ab-FITC in 37 C in homogeneous format. After changing the pH to separate the polymer-immune complex precipitate, it was re-dissolved and determined by fluorescence method. The results showed that the immobilization efficiency, immunological reaction activities of immobilized Au and phase transition pH range were improved as Ag was immobilized by thermal initiation instead of redox initiation polymerization. Under optimum conditions, the calibration graphs for the Ag in both methods, thermal initiation and redox initiation, were linear over the concentration range of 0.0-1000 ng mL(-1), with detection limits 8 (thermal initiation) and 12 ng mL(1) (redox initiation), respectively. Moreover, some pH-sensitive polymer prepared only in organic solvent or under high temperature could also be used as an immunoreaction carrier by thermal initiation polymerization. Thermal initiation polymerization was a better immobilization mode. (C) 2004 Elsevier B.V. All rights reserved.

Polymerization of ionic liquid-based microemulsions: A versatile method for the synthesis of polymer electrolytes

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