降冰片烯及其衍生物开环易位聚合的研究进展

A Review of the Ring-opening Metathesis Polymerization Involving Norbornene or Its Derivatives

环烯烃开环易位聚合(ROMP)是指在金属催化剂存在下,环烯烃中的碳碳双键断裂并重新结合形成新的分子,得到的聚合物中留有不饱和双键,具有活性聚合的特点。ROMP是改造碳碳双键最有效的手段之一,极具特色且广泛应用于高分子材料与有机分子的合成。关于环烯烃ROMP研究早在20世纪50年代就已开始,当时的研究主要集中在以Ti、Re、W、Mo等过渡金属配合物组成的Ziegler-Natta催化体系引发环烯烃ROMP。20世纪80年代中期以后,研究则以亚烷基类或卡宾型类催化剂为主,其引发环烯烃ROMP的机理更加清晰。随着结构明确、稳定高效的环烯烃ROMP催化剂的开发与完善,该领域的研究焦点开始转向环烯烃ROMP适用单体的拓展以及所得聚合物的应用。在环烯烃ROMP研究中,降冰片烯及其衍生物是研究最多和应用最广的一类单体,这是因为它们的反应活性较高,来源丰富,价格也不昂贵。除研究拓展ROMP适用单体外,研究者主要从降冰片烯基单体的空间位阻、化学构型、侧基极性以及与其他环烯烃或降冰片烯基单体共聚改性等方面不断进行尝试,同时充分发挥环烯烃ROMP优势,与其他聚合方法联用,不断改善所得聚合物的性能并将其应用于不同研究领域。降冰片烯及其衍生物ROMP在阻燃材料、交换膜、纳米材料、生物医药等领域已取得一系列研究成果,其中在阻燃材料领域研究最早且许多产品已经工业化。在交换膜领域,由于降冰片烯基聚合物膜的热稳定性、耐酸碱性和电导率均较好,目前的研究主要是探索如何在燃料电池中获得应用。纳米材料是近年来最热门的研究领域之一,降冰片烯基纳米金属聚合物材料和纳米磁性聚合物材料等已有初步应用。在生物医药领域,降冰片烯及其衍生物极具发展前景,目前的研究主要集中在药物传输材料,已有初步的研究成果,但要实现工业化尚待进一步研究。此外,基于降冰片烯及其衍生物的接枝聚合物、嵌段聚合物、液晶聚合物、导电聚合物等也获得人们越来越多的关注。本文简要介绍了降冰片烯及其衍生物ROMP的反应机理,以及ROMP催化剂从多组分到钼、钨系再到钌系等几个发展阶段,详细综述了降冰片烯及其衍生物ROMP在上述若干领域的研究进展,并在此基础上简要探讨了今后研究与开发应用的新方向。

Ring-opening metathesis polymerization(ROMP)of cyclic olefins,a well-established reaction,is one of the most effective means to transform carbon-carbon double bonds and has been widely used in polymer science and organic chemistry.ROMP of cyclic olefins occurs in the presence of a metal carbene catalyst which breaks the carbon-carbon double bonds of the cyclic olefins and connects them into new unsaturated polymers.The research over the cyclic olefins metathesis polymerization was initiated in the 1950s,focusing originally on the catalytic polymerization of cyclic olefins using Ziegler-Natta catalytic systems consisting of transition metal complexes mainly based on Ti,Re,W,Mo,etc.Since the middle of the 1980s,the investigations were concentrated on the polymerization mechanism and alkylidene or carbene catalysts.With the establishment of well-defined,stable and efficient catalysts,the researchers’concern has been turned to new applications of cycloolefin polymers,and also to developing new cycloolefin ROMP monomers.For the ROMP reaction,norbornene and its derivatives have been studied extensively since they are highly reactive,easily accessible and relatively low-cost.Besides the expansion of the monomer species available for ROMP,continuous research endeavors have been made to enhance the ROMP resultant polymers’performance and application potential,mainly from the aspects of the steric hindrance,chemical configuration,pendant polarities of norbornene-based monomers,and the copolymerization of other cyclic olefins or norbornene-based monomers,as well as conjunction with other polymerization methods.The ROMP of norbornene and its derivatives also made certain advances in the fields of flame retardancy,ion exchange or proton exchange membranes,nanomaterials,biomedical materials and so on,in which flame retardant materials made from norbornene or norbornene derivatives have long been researched and broadly achieved industrialization.In the field of exchange membranes,researchers concentrate on applying norbornene-based polymer membranes to fuel cell due to their thermal stability,acid and alkali resistance,and electrical conductivity.Nanomaterials is one of the most popular research fields in recent years,and nano-metal/polymer composites and magnetic polymer nanocomposites have realized tentative application.The biomedical materials especially drug delivery systems which involve norbornene derivatives have displayed impressive potential,though the industrialization and commercialization still deserve further exploration.Additionally,the norbornene-derivative-based graft polymers,block polymers,liquid crystal polymers,and conductive polymers have also drawn researchers’attention.We herein briefly describe the reaction mechanism of ROMP with norbornene and its derivatives as monomer,as well as the ROMP catalysts’multistage development,i.e.multi-component catalytic systems,molybdenum-or tungsten-based catalytic systems,and ruthenium-based catalytic systems.Moreover,the paper mainly focuses on the recent research progress of ROMP process and products with respect to the norbornene species in the above mentioned fields,and ends with a prospective discussion over the expected new directions of this emerging research topic.