功能化聚乙烯高性能导向的镍钯催化剂与极性单体双重开发

Coordination copolymerization of polar monomers with ethylene is an efficient and crucial method to directly achieve the functionalization and high-performance of polyethylene commonly-used material. The lower oxophilic and more functional group tolerant late-transition metal nickel and palladium complexes are one of the most promising catalysts for catalyzing this type copolymerization. However, as one of the frontier topics in polymer science, a long-standing challenge in this field is how to increase the polymerization activity and enhance the polymer molecular weight that is a prerequisite for preparing high-performance functionalized polyethylene with adjustable incorporation of polar monomer. In this project, dual exploitation on both novel nickel and palladium catalysts chelated by phosphine sulfonates and polar monomers will be performed for the first time. For the catalysts, three efficient strategies such as introducing suitable bulky substituents into the ligand framework, building the weak interaction of ligand with metal center, and building the interaction of polar monomer with metal center are employed; and for the polar monomers, 1,5-, 1,6-, 1,7-di-substituted polar di-vinyl monomers with or without cross-linkable moieties are designed. The aim is to improve these notorious intrinsic limitations such as chelation of functional group, sluggish chain growth, and rapid beta-H elimination in the copolymerization reaction of ethylene with polar monomers. As a result, not only the copolymerization activity will be increased but also the molecular weight of copolymer with adjustable incorporation will be enhanced, which can realize the synthesis of high-performance functionalized polyethylene. Based on both the stoichiometric insertion reaction of polar monomers, kinetic analysis, isolation of active species and the density function theory (DFT) calculation, the plausible mechanism of polymerization reaction will be elucidated and the relationship of catalyst-monomer-polymer structure-polymer property will also be revealed.

极性单体与乙烯配位共聚合是直接实现聚乙烯通用材料功能化、高性能化的重要途径。亲氧性更弱和极性基团容忍度更高的后过渡金属镍钯配合物催化该类共聚反应具有前途。如何提高聚合活性与共聚物分子量，制备单体插入率可调的高性能功能化聚乙烯是高分子科学的前沿课题和聚烯烃领域长期存在的难题。本项目率先从设计开发膦磺酸镍钯催化剂(采用合适大位阻取代基策略、配体与中心金属作用策略、极性单体与中心金属作用策略)与极性单体(采用1,5-、1,6-、1,7-、含可交联基团的极性二乙烯基单体)双重手段入手，旨在同时改善乙烯与极性单体共聚合反应中存在的极性基团螯合、链增长慢、beta-H消除快等限制问题，实现聚合活性的提高、共聚物分子量的提高、以及极性单体插入率的可调，进而实现功能化聚乙烯的高性能化。借助单体定量插入反应动力学、活性种分离和DFT计算，阐明聚合反应机理，揭示催化剂-单体-共聚物结构-共聚物性能四者关系。

高性能聚烯烃材料（包括功能化聚烯烃、聚烯烃弹性体与超高分子量聚乙烯）是国家十四五规划的重大需求化工材料。如何发展新催化剂、新单体、新方法，创制高性能聚烯烃材料是学术界与工业界长期关注的研究方向，也是高分子学科领域的重要方向。本项目聚焦后过渡金属催化乙烯聚合及乙烯与极性单体共聚合领域的链行走、链转移、极性单体问题关键科学问题，设计合成了多类新型[P,O]、[N,N]与[N,O]镍钯催化剂，开发了多种极性烯烃单体，采用了新聚合方法，制备出差异化的高性能聚烯烃材料；并通过实验与理论计算相结合，阐明聚合反应机理，揭示催化剂-单体-聚合物结构与性能之间关系。项目取得的关键突破与重要的学术价值凝练如下：（1）发展精准控制链行走的镍系催化剂，在国际上首次实现乙烯作为唯一单体在工业条件下（30-90度）精准制备乙丙弹性体（选择性>99%，支化数达220/1000C）；学术上解决了过去25年链行走聚合支化不可控难题，工业上避免了共聚单体的使用与简化了反应工艺。（2）发展温度耐受性达200度纪录值的镍催化剂，将烯烃活性聚合温度窗口大幅提升到130度，并制备半结晶超高分子量聚乙烯（>100万），解决了烯烃聚合70余年的高温快速链转移难题；发展了乙烯聚合活性达10的9次方纪录值的镍催化剂，媲美工业应用上的茂与非茂金属催化剂。（3）发展高效共聚的镍钯催化剂，精准（>99%）创制主链官能化超高支化乙烯/丙烯酸酯与乙烯/醋酸乙烯酯共聚物；采用极性添加剂作为链结构调节剂，精准合成嵌段(无定型超高支化乙烯/丙烯酸甲酯共聚物)-(半结晶轻度支化乙烯/丙烯酸甲酯共聚物)；首次在常压1bar温和条件下，创制功能化超高分子量聚乙烯（>100万）；首次将乙烯、丁二烯、二氧化碳3种大宗工业单体同时嵌入至聚合物链段中，制备功能化聚乙烯；为极性单体问题的解决与可控链结构功能化聚烯烃的合成提供了新思路与新方法。