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研究了丁二烯在苯中有四碘化钛-三异丁基铝催化剂的存在下的聚合。发现这一催化体系的活性取决于Al/Ti比和聚合温度。对每一四碘化钛用量出现一具有最高活性的“临界Al/Ti此”;低于这一Al/Ti比,活性完全消失;高于这一Al/Ti比则活性逐渐降低(图2)。 增加Al/Ti可以减慢聚合速度而不影响最终转化率(图3);因此,可以利用Al/Ti来控制这一聚合反应以防止反应混合物的积热现象(图4)。 这一催化体系的优点是不论在任何条件下,包括催化剂组成(例如Al/Ti)和聚合条件(例如温度),聚合物都不合凝胶,而顺-1,4-结构含量总能在90％以上(表2)。 聚合物的分子量取决于两个主要因素:四碘化钛用量和聚合温度;增加四碘化钛用量和升高聚合温度都降低分子量(图5和图6)。Al/Ti对分子量的影响则不甚明显(图6)。 用这种催化剂制得的顺-1,4-聚丁二烯的分子量分布很窄(图7);因此,虽然这是一个非均相催化体系,它的活性中心可能比较单纯,大概不会含有多种活性中心。
The polymerization of butadiene in the presence of a titanium tetra-titanium triisobutylaluminum catalyst in benzene was studied. The activity of this catalytic system was found to depend on the Al / Ti ratio and the polymerization temperature. A “critical Al / Ti” with the highest activity was present for every amount of titanium tetraiodide; below this Al / Ti ratio, activity disappeared completely; activity above this Al / Ti ratio decreased gradually (Figure 2 ). Increasing Al / Ti slowed the rate of polymerization without affecting the final conversion (Figure 3); therefore, Al / Ti could be used to control this polymerization to prevent the build-up of the reaction mixture (Figure 4). The advantage of this catalytic system is that the polymer will not gel and the cis-1,4-structure content will always be 90% whatever the conditions, including the catalyst composition (eg Al / Ti) and the polymerization conditions % Or more (Table 2). The molecular weight of the polymer depends on two main factors: the amount of titanium tetraiodide used and the polymerization temperature; increasing the amount of titanium tetraiodide and increasing the polymerization temperature both decrease the molecular weight (Figures 5 and 6). The effect of Al / Ti on the molecular weight is less pronounced (Figure 6). The cis-1,4-polybutadiene produced with this catalyst has a very narrow molecular weight distribution (Figure 7); therefore, although this is a heterogeneous catalytic system, its active site may be relatively simple, probably not Contains a variety of active centers.