摘要
H_2对烯烃聚合活性的影响是由于"β-agostic"作用,使聚合中形成的基团Ti—CH(R)CH_3(R为H,CH_3)相对稳定,称为休眠的活性位,在H_2存在下,可以使其重新活化,生成Ti—H。对于丙烯聚合,丙烯1,2插入Ti—H,生成Ti—CH_2—CH_2—CH_3,使其活化,提高丙烯聚合活性。在丙烯聚合过程中,催化剂的氢调敏感性的影响因素和机理较为复杂,与聚合过程中丙烯的区域不规则2,1插入的发生几率有关,以二醚为内给电子体的催化剂发生2,1插入的可能性大,所以氢调敏感性高。另外,研究证实,H_2是以原子的形式起链转移作用,在催化剂合成中加入微量的氢解离剂,可以加速H_2的解离,提高催化剂的氢调敏感性。
The influence of hydrogen on polymerization activity is exerted through β-agostic interaction between hydrogen atoms of one of its CH3 groups and Ti, which makes the Ti-CH（R）CH3（R=H or CH3） groups formed in polymerization be relatively stable and be regarded as ＂dormant active center＂. In the presence of hydrogen this center can be activated again and form Ti-H bond. In the case of propylene polymerization, once a propylene molecule inserts into the Ti-H bond, an active Ti-CH2-CH2-CH3 comes into being and the polymerization activity ofpropylene increases due to the activation of this group. In the process of propylene polymerization, the influential factors and action mechanism of hydrogen response of the catalyst seem to be rather complicated, concerning probability of regioirregular 2,1 insertions in propylene polymerization. The catalyst with diether as internal electron donor has a good hydrogen response because of the higher possibility of 2,1 insertions in the growing polymer chain. In addition, the relevant studies confirm that only the hydrogen in the form of atom can play a role in the chain transfer reaction. Adding a trace amount of dissociation agents in the synthesis of catalysts can accelerate the dissociation of hydrogen molecules, thereby improving the hydrogen response of the catalyst.
出处
《合成树脂及塑料》
CAS
北大核心
2011年第6期64-69,共6页
China Synthetic Resin and Plastics
