DNBP给电子体构象分析及在Ziegler-Natta丙烯聚合中作用机理研究

首次采用TINKER构象搜索和DFT结构优化相结合方法,基于对Ziegler-Natta丙烯聚合催化体系邻苯二甲酸正丁酯(DNBP)给电子体快速搜索出的1 023种构象,筛选出其优势构象,减少了给电子体初始稳定结构搭建模型的盲目性和随机性.采用DFT方法,对DNBP两种构象与MgCl2载体相互作用及丙烯插入立体选择性机理进行了研究.结果表明,DNBP构象影响其在MgCl2表面的吸附,s-顺、反式构象可以单齿、桥连和螯合方式吸附在MgCl2(110)表面;s-顺、顺式仅存在桥连吸附.双氯原子缺陷载体模型上TiCl4吸附的稳定性高于DNBP,成为可能的活性中心;给电子体对活性位的作用与其吸附方式有关,DNBP以桥连方式吸附在Ti的邻位,可将无规活性中心有效转化为等规活性中心,而螯合方式不能改善催化剂的立体结构和区域选择性.     

Modification of the (SiO<Subscript>2</Subscript>/MgO/MgCl<Subscript>2</Subscript>)·TiCl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Ziegler-Natta polyethylene catalysts using the third metal elements

Various (SiO₂/MgO/MgCl₂)·TiCl _x Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified (SiO₂/MgO/MgCl₂)·TiCl _x Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher α-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution (MWD) and the lowest average molecular weight (MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.     

程序升温反应法由纳米氧化铁制备纳米氮化铁

先以廉价的无机铁盐为主要原料,采用沉淀法和溶胶凝胶法制备纳米氧化铁粒子,由此得到粒径大小在10～20nm,20～40nm和40～60nm的氧化铁,在此基础上,以纳米氧化铁为前体,在氨气气氛下由程序升温反应法制备纳米氮化铁.研究发现,纳米氧化铁经程序升温反应氮化后,可以制备出纳米尺度的氮化铁.不同大小的氧化铁纳米粒子氮化后尺寸存在明显的差异,在一定范围内,小粒径的纳米氧化铁氮化后更容易长大;对于大小相近的γ相与α相纳米氧化铁粒子,γ氧化铁纳米粒子氮化后尺寸增大更为显著.制得的氮化铁的形貌与其氧化铁前体保持一致.     

掺钕石英光纤中的1.08μm超辐射

用Ar离子514.5nm激光泵浦,在掺钕石英光纤中产生了1.08μm的超辐射,产生的最大输出功率6mW,线宽3nm。实验结果和理论拟合较好。