水杨醛亚胺镍配合物催化的乙烯水相聚合

在含表面活性剂的水相体系中, 用一系列水杨醛亚胺镍配合物催化乙烯聚合, 得到了高分子量低支化度聚乙烯. 研究表明水杨醛亚胺镍配合物中苯环上取代基的电子效应和空间位阻对乙烯聚合活性和聚合物的分子量有所影响. 提高配合物酚氧环上取代基的吸电子性, 聚合活性相应增加, 但聚乙烯的分子量降低; 而增加苯胺环上取代基的空间位阻, 聚合活性和聚乙烯的分子量均增加. 粘度法测得由水相聚合得到的聚乙烯的分子量在10⁴～10⁵范围内. DSC测得该聚乙烯的结晶度在50%～70%之间, 熔点在115～137 ℃范围内. GPC分析表明用环辛二烯合镍Ni(COD)₂]助催化乙烯, 聚乙烯的分子量分布随酚氧环上取代基电负性增加而从双峰到单峰变化, 动态流变学研究进一步说明了聚乙烯分子量及其分布的变化.

Aqueous Catalytic Polymerization of Ethylene by Neutral Nickel(II) Complexes

Aqueous polymerizations of ethylene catalyzed by a series of neutral nickel(II) complexes coordinated with salicylaldimines have been performed in the presence of surfactants, and the lower branched high molecular weight polyethylene was obtained. The results showed that the catalytic activity of the catalysts and the properties of the polyethylene were influenced by the electronic and steric effects of the substituents attached on the benzene ring in the complexes. With increasing the electron withdrawing substituents in the phenoxy ring, the catalytic activity was increased, and the molecular weight of polyethylene decreased. Meanwhile, both of the catalytic activities and the molecular weights of polyethylene were increased with increasing the steric effect of the substituents in aniline. The molecular weights of the polyethylene obtained in an aqueous system were in the range of 10⁴～10⁵. The DSC analysis of the polyethylene indicated that the degrees of crystallinity and the melting points were 50%～70% and 115～137 ℃, respec-tively. The GPC results displayed that the molecular weight distribution of the polyethylenes cocatalyzed by bis(1,5-cyclooctadiene)nickello)Ni(COD)₂] presented bimodal to unimodal with the electronegativity of the groups attached on the phoenxy circle being increased. The variation of the molecular weight and polydispersity of the polyethylenes were further demonstrated by the dynamic rheological researches.