Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

A family of cobalt(II) complexes supported on tridentate dibenzimidazolyl ligands having a general formula: [N(CH₃)(CH₂)₂(Bm-R)₂]CoCl₂ (where Bm = benzimidazolyl, R = H; -Me; -Bz), have been prepared by the condensation of o-phenylene diamine with methyliminodiacetic acid. The Co(II) complexes exhibited high activities for the polymerization of 1,3-butadiene, on activation with ethylaluminum sesquichloride (EASC), to yield predominantly cis-1,4 microstructure. The polymers are characterized by high molecular weight with polydispersity values between 2.35 and 3.37. The ligand modification shows remarkable influence on polymerization activity. The stereospecificity of the catalysts is consistent for a wide range of reaction conditions, except temperature. The electronic influence of ligand structure towards metal center is investigated by using cyclic voltammetric analysis and the generation of cationic active centers is identified via UV-vis spectroscopic analysis of the catalyst system.     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Ultra high cis polybutadiene by monomeric neodymium catalyst and its tensile and dynamic properties

The monomeric Nd-catalyst composed of Nd(neodecanoate)₃·(neodecanoic acid)(NdV4)/AlEt₂Cl/Al(iBu)₃ showed a high activity (2.0×10⁶ g/Nd mol h), and the monomeric active-center was proposed through density functional calculations (B3LYP/CEP-31G). The microstructure of polybutadiene was controlled by chain-transfer with NdV4, catalyst composition and phosphine compounds. As with increase in Nd concentration, increase in branchness and decrease in cold-flow were observed. A series of phosphine compounds was employed to control the microstructure of polybutadiene, and ultra high cis polybutadiene with over 99% cis content was obtained in the presence of tri-p-fluorophenyl phosphine.The vulcanized properties of different microstructured polybutadienes were measured. Linear polymer, Nd-BR1, showed excellent tensile and dynamic properties such as low heat build-up and high abrasion resistance. However, poor processibility in view of high compound viscosity and hardness was obtained. Nd-BR2, designed to compromise both processibility and physical properties, exhibited improved processibility in terms of low compound viscosity with good tensile and dynamic properties.     

复合调节体系对聚丁二烯反应动力学及微观结构的影响

以正丁基锂为引发剂、环己烷为溶剂,采用阴离子聚合工艺进行了丁二烯的均聚.考察了不同复合结构调节体系(SDBS/THF,SDBS/TMEDA)对聚合反应动力学和聚合物微观结构(1,2结构含量)的影响.结果表明,采用复合结构调节体系可加快聚合反应,缩短聚合时间,同时可在较大范围内调节聚合物的1,2结构含量.     

聚合釜的密封改造

乙烯顺丁橡胶装置聚合釜因其介质关系,对密封的使用及性能提出了较高的要求,实际应用与试验证明,一般填料密封不适合聚合釜使用。以填料密封与波纹管机械密封的组合形式,可解决聚合釜密封的泄漏问题,延长密封的检修时间,为装置增加较好的效益。     

聚苯醚/聚丁二烯共混物及其复合材料的性能研究

采用DMA和SEM等手段研究了聚苯醚(PPO)与聚丁二烯(PB)共混体系的相容性,测试了共混物的流变性能,玻璃纤维增强复合材料的介电性能、力学性能、耐溶剂性和吸水率.结果表明:在聚苯醚与聚丁二烯的共混切中加入相容剂可以有效的提高共混物的相容性,共混物的溶解温度宜控制在50～60℃;复合材料层压板具有优异的介电性能、较好的力学性能、良好的耐溶剂性能和低的吸水率.PPO/PB共混物与玻璃纤维之间具有良好的界面粘结性能.聚苯醚的含量对共混体系的介电性能有一定的影响.随着PB的加入,使得复合材料的耐溶剂性能得到很大的改善.     

Studies on Mechanical,Thermal, and Flame Retarding Properties of Polybutadiene Rubber (PBR) Nanocomposites

An effect of nanosize CaCO₃ on physical, mechanical, thermal and flame retarding properties of PBR was compared with commercial CaCO₃ and fly ash filled PBR. CaCO₃ at the rate of 9, 15, and 21 nm were added in polybutadiene rubber (PBR) at 4, 8 and 12 wt.% separately. Properties such as swelling index, specific gravity, tensile strength, Young's modulus, elongation at break, modulus at 300% elongation, glass transition temperature, decomposition temperature, flame retardency, hardness, and abrasion resistances were determined. The swelling index decreased and specific gravity increased with reduction in particle size of fillers in PBR composites. There was significant improvement in physical, mechanical, thermal and flame-retarding properties of PBR composites due to a reduction in the particle size of fillers. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt.% of filler loading. This increment in properties was more pronounced in 9 nm size CaCO₃. The results were not appreciable above 8 wt.% loading of nano fillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider some thermodynamically aspects of resulting system. The cross-linkage density has been assessed by Flory-Rehner equation in which free energy was increased with increase in filler content.     

From Cross‐linking to Plasticization – Characterization of Glycerin/HTPB Blends

Usually, a plasticizer is a relatively low‐viscosity liquid ingredient that is added to improve the mechanical properties and the processing properties of a propellant, such as a lower viscosity for casting or a longer pot life of the mixed, but uncured propellant. The effects of many plasticizers on the performance of the composite propellant have been studied in detail. Glycerin is a triol, a low viscosity material, and inexpensive. It seems that the processing properties and the mechanical properties of the HTPB binder would be improved by the addition of glycerin. The curing behavior, the mechanical properties, and the thermal decomposition of a glycerin/HTPB blend have been investigated in this study. The viscosity of the glycerin/HTPB blend and the increasing ratio of the viscosity versus the elapsed time are lower than those of only HTPB. The mechanical properties are improved by the addition of glycerin, even for a low quantity of glycerin. The thermal decomposition behavior of the blend occurs at lower temperatures when compared to that of HTPB.     

聚丁二烯胶乳的辐射硫化

用60Co辐射硫化聚丁二烯胶乳(Polybutadiene latex,PBL)制备全硫化粉末橡胶(Fully vulcanized polybutadiene rubber particles,FVBR),并研究胶乳的交联行为.用动态激光光散射仪和原子力显微镜(Atomic force microscopy,AFM)观测粒径尺寸、粒径分布与形貌,并用力学和动态力学(Dynamic mechanical analysis,DMA)测试仪分析了交联对宏观力学及其动态力学性能的影响.结果表明,辐射交联使胶乳粒子体积收缩,并随吸收剂量增加胶膜的体积溶胀倍率(Qv)和交联点间平均分子量(Mc)减小;而交联密度(Ve)和凝胶含量增大.随着交联密度的增加,抗张强度和断裂伸长率降低,杨氏模量(E)和硬度(Shore A)则增大;其弹性模量(Er)增加,而动态损耗峰(Tan δ)变窄.PBL辐射交联行为在吸收剂量低于200kGy范围内符合Charlesby-Pinner关系式,为无规交联.     

THE IMPORTANCE OF SOLVENT COMPOSITION AND ADSORPTION EFFECTS ON THE FLOW PROPERTIES OF

Capillary rheometry data are presented for concentrated solutions of polybutadiene dissolved in mixed volatile solvent systems composed of benzene, butadiene, and butene 1. Unusual flow phenomena, associated with polymer adsorption at capillary tube walls, are observed for polybutadiene in a solvent composed of benzene and butene 1, but not observed at the same polymer concentration in a pure benzene solvent or for a mixed binary solvent where the butene 1 is replaced by butadiene. The unusual flow phenomena include a diameter dependency in the viscosity measurements when end effects are eliminated, and a diameter dependency in the end correction itself. Correction of the diameter dependent viscosity data is successfully made by postulating an effective negative slip velocity (polymer adsorption). The thickness of the polymer adsorbed layer relative to the tube diameter is of the same order as observations for other polymer solutions both in capillary and packed bed flows. It is argued that the flow phenomena observed in the polybutadiene-benzene-butene 1 solutions and not observed in the polybutadiene-benzene-butadiene solutions of identical composition is related to the solvent system itself—benzene and butadiene being a good mixed solvent for polybutadiene relative to benzene and butene 1 in the same ratio. The work was initiated and completed in response to material handling problems encountered in a commercial process for the manufacture of polybutadiene.