摘要/Abstract
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.
关键词: 烷基铝, 异戊二烯, 催化, 齐聚, 聚合行为
Alkylaluminium (AlR3), as co-catalyst component in Ziegler-Natta catalytic system, plays important roles in the alkylation, forming and changing the structure and concentration of active centers through the reduction and reversible adsorption-desorption reactions with the metal compound of the catalyst, acting as chain transfer agent, etc. However, the alkylaluminium itself do have the catalytic effect on the conjugated diene monomers. In this article, alkylaluminium with different structures such as triethylaluminium (AlEt3), triisobutylaluminium (Al(i-Bu)3), diisobutylaluminium hydride (AlH(i-Bu)2), diethylaluminium chloride (AlEt2Cl), ethylaluminium dichloride (AlEtCl2) were used to catalyze isoprene oligomerization and polymerization. The effects of the structure and concentration of alkylaluminiums (n(Al)/n(M)=7×10-5, 35×10-5, 350×10-5, 1050×10-5) on the catalytic behaviors of isoprene were studied. The microstructure (trans-1,4 and cis-1,4), molecular weight and molecular weight distribution of the products were characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC) and gas chromatography-mass spectrometry (GC-MS). It was found that alkylaluminium could initiate oligomerization and cationic polymerization of isoprene under the minor incorporation of H2O, which were affected greatly by the structure and concentration of alkylaluminium. Using AlEtCl2 led to the highest catalytic activity and produced products containing more linear polymers with mixed cis-1,4/trans-1,4 structures when n(Al)/n(M)=1050×10-5. The Al(i-Bu)3 and AlH(i-Bu)2 didn't have basically cation initiation ability, which led to isoprene oligomerization. The alkylaluminium with n(Al)/n(M) ≤ 350×10-5 had negligible influence on the isoprene polymerization and oligomerization. And lower or higher alkylaluminium concentration were not beneficial to obtain polyisoprene with high molecular weight. The catalytic mechanism of alkylaluminium on isoprene was discussed, which provided a further understanding on the catalytic behavior of alkylaluminium components in Ziegler-Natta catalyst and the effect of alkylaluminium on polymers.
Key words: alkylaluminium, isoprene, catalysis, oligomerization, polymerization behavior
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