边臂策略在聚烯烃催化剂设计中的应用

Sidearm Approach to the Synthesis of Catalysts Used in Olefin Polymerization

提出用"边臂"策略设计和改造烯烃聚合催化剂,以钛、镍等配合物为模型,系统研究了边臂基团对配合物的配位模式、配合物的稳定性,对乙烯均聚活性以及乙烯与α-烯烃、环烯烃以及极性单体共聚合的活性和对聚烯烃的结构与性能的影响.研究结果表明通过边臂基团可以调节催化中心的空间形状和电子特性,实现对催化物种性质的控制与调节,调控烯烃聚合活性和聚烯烃的结构与性能.

Catalyst design for single-site olefin polymerization is of great scientific and industrial importance, and has attracted much attention since the pioneering work of Ziegle-Natta. ＂Sidearm strategy＂ developed in the last decades has been used successfully for designing homogenous catalyst. By which, a ＂sidearm＂ group is introduced to a basic unit, and the performance of the active center could be improved readily by modulate its shape and/or the electronic properties. This review article discloses the application of sidearm strategy in olefin polymerization catalyst design. Modification of a simple bidentate salicylaldeminate by a coordination group（OR, SR, Se R, PPh2） induced the coordination pattern variation. Of the newly-designed salicylaldiminato titanium trichlorides, both steric and electronic properties of the active species were proved to be readily tunable. Sidearm effect was obviously seen. For example, hard and small oxygen as a donor atom in sidearm induced moderate catalytic activity（104 g PE/mol（Ti）·h·atm） when it was used to polymerize ethylene in the presence of MMAO, whereas the complexes with soft and large S, Se, and P atoms as donor atom showed much higher activity（106 g PE/mol（Ti）·h·atm）. The sidearm effect on thermostability of the complexes was also observed. In addition, the capability of catalyzing ethylene/comonomers（α-olefin, cycloolefin） copolymerization was also sidearm dependent. Both the activity and the incorporation of a comonomer could be improved by replacing the sidearm from bulky ―Si Pr to ―Sn Pr. The newly designed titanium trichloride complexes was proved to have good polar group tolerance. Consequently, ω-alkenol, ω-alkenoic acid, and ω-alkenoic ester etc. could be incorporated into PE backbone efficiently. By this way, PPh2― and AsPh2― were zipped on polyethylene efficiently, which was proved to be efficient in catalytic [3 ＋ 2] cycloaddition and Wittig reaction, separately. This is a simple way for the preparation of readily recovered and reused PE-supported organocatalyst. The strategy was also extended to the modification of SHOP-type catalysts, and nickel complexes bearing an alkyloxyl group as a sidearm were synthesized. The distance between Ni and O（R） is shorter than the sum of van der Waals radii of Ni and O（2.985 A versus 3.15 A）, indicating a weak interaction between O（R） and Ni atoms. Further studies showed that the introduction of alkoxyl group improved the activity and thermostability. Based on the optimized metal complex, heterogeneous titanium catalyst was developed and used in production of ultra-high molecular weight polyethylene（UHMWPE）, which is highly linear and readily processible.