摘要
研究钨系催化剂合成1,2-聚丁二烯的紫外可见光谱特征的结果表明,在紫外可见光区,WCl_6-C_4H_9OH体系存在W(V)特征吸收峰,加入烷基铝使该峰减弱、消失,在还原型吸收封线区内,体系具有聚合活性;烷基铝上引入CH_3PhO^-或RO^-基团,其还原能力降低;体系中加入丁二烯陈化,有助于W(V)的还原。
The activity of tungsten catalyst system for polymerization of butadiene (Bd) into 1,2 -polybutadiene was studied by ultraviolet -visible ( UV - Vis) spectrometry . Figure 1 showsthe UV -Vis absorption spectra of WC16-C4H9OH-Al(i-Bu)3 .Curve a is the spectrum of WCl6-C4H9OH in hydrogenated gasoline .The characteristic absorption bands of W (V) complex are based on the principle of ligand theory , two bands , at 625 nm and 910 nm , should be asigned to the d- d spin - allowed transition of W (V ) located in the center of the irregular octahedron ; and the band at 400 nm is related to the charge transfer band between ligand C4H9O- and W(V), also called σ-σ transition .In WCl6-C4H9OH-Al(i-Bu)3 system ,the spectra ( Figure 1) shown curves from b to g for different molar ratio of Al /W indicate that with the increase of Al/W one of the characteristic bands ofW(V),i .e.,the peak at 625 nm ,turns out to be a high shoulder - shape until disappearance , when Al/W> 1.5 ,another peak at 910 nm is also vanished .The curves from f to g are called redox curve , the results of polymerization tests confirm that in the region of the redox curve for Al/W>2.5 ,the catalyst system shows rather high activity of polymerization .From the comparasion of the spectra inWCl6-C4H9OH-Al(i-Bu)3 system with those in WC16 - C4H9OH - AlEt3 , - AlEt2Cl , or - Al(i-Bu)2 H systems ,the order of the reductive ability of aluminium alkyls is shown as : Al( i - Bu)3 > AlEt3 > AlEt2Cl > Al (i - Bu )2H From the comparison of the polymerization activity of WC16 - C4H9OH - Al (i - Bu )3 system with that of WCl6-C4H9OH-Al(i-Bu)2OPhCH3 system , it can be found that the range of Al/W in respect to the catalytic activity in WC16-C4H9OH- Al( i-Bu )2OPhCH3 system is broadended due to presence of function group CH3PhO-, forming more stable active center complexes .The absorption spectra of WCl6-C4H9OH-Bd-Al(i-Bu)3 system are shown in Figure 2, the variation of spectra is analogous to that in Figure 1, but the value of peak at 625 nm increases more rapidly ,this is owing to the presence of Bd in the system , but it disappears as soon as Al/W > 1 ,which is considered that the reduction of W (V) complexes might be improved in the system .
出处
《合成橡胶工业》
CAS
CSCD
北大核心
1992年第3期164-168,共5页
China Synthetic Rubber Industry
基金
国家自然科学基金
关键词
聚丁二烯
催化剂
六氯化钨
烷基铝
tungsten hexachloride
aluminium alkyls
ultroviolet - visible spectrometry
1,2 - polybutadiene
Ziegler - Natta catalyst
