Insertion polymerization of electron-deficient vinyl monomers

乙烯和丙烯的催化聚合是研究得最多的化学反应之一。与之形成鲜明对比的是，缺乏电子的极性取代乙烯基单体的插入聚合是一个长期存在的挑战。直到最近，乙烯与包括丙烯酸在内的多种单体的线性共聚才得以实现。在第一个资助期内，对控制插入链生长和催化剂失活的因素获得了全面的了解。催化剂设计先进，新型高分子材料不断发展。我们现在专注于克服极性乙烯基单体插入（共）聚合的固有限制。游离单体官能团的配位，特别是插入产生的重复单元的配位，可逆地阻断配位位点并阻碍催化作用。为了克服这个问题，在催化剂中选择性地结合官能团到适当的位置。在中性Pd（II）催化剂的双齿配体中，单体的官能团与精心放置的互补氢键基序的相互作用有利于烯烃配位，而不是进入的单体官能团的结合。将这一概念扩展到已经结合的单体的极性基团，目的是将它们的结合从螯合配位阻断活性位点转移。解决这一问题的另一种方法——也可能提供新的共聚物微观结构——是乙烯插入链生长与极性单体段自由基生长的结合。Monteil （Macromolecules, 2011, 44, 3293）认为中性Ni（II）水杨酸醛配合物可使乙烯和甲基丙烯酸甲酯（MMA）聚合成（多）嵌段共聚物。我们的初步研究证实，乙烯的插入链生长和甲基丙烯酸甲酯的自由基聚合是同时发生的，这两个反应是相互依存的。为了阐明此处的作用机制并设计插入/自由基“穿梭”聚合的一般概念，将结合聚合物端基分析，研究（13C标记的）ni -芳基和ni -甲基前体的聚合。此外，金属在产生和清除自由基中的作用将通过为此目的制备的（水杨醛缩）Ni(I)物种的研究来阐明。这包括它们在聚合条件下的反应性以及与插入链生长的活性物质的化学计量反应。为丙烯建立的空间填充排斥相互作用的立体控制不适用于此。我们已经设计了一个不对称取代适度体积的p供体毗邻结合烯烃作为控制丙烯酸酯插入的概念。这可以作为一个起点，通过远程刚性连接器开发立体规则链生长。在进一步的过程中，前面提到的吸引相互作用的概念可以发挥作用。

Catalytic polymerization of ethylene and propylene is one of the most well-studied chemical reactions. By stark contrast, an insertion polymerization of electron deficient polar-substituted vinyl monomers is a long-standing challenge. Only recently, linear copolymerizations of ethylene with a scope of monomers including even acrylic acid have been realized. In the first funding period a comprehensive picture was gained of factors governing insertion chain growth and catalyst deactivation. Catalyst design was advanced and novel polymeric materials evolved. We now focus on overcoming the identified intrinsic limitations of insertion (co)polymerization of polar vinyl monomers.Coordination of the functional group of the free monomer, and in particular of the repeat units gener¬ated by insertion, blocks coordination sites reversibly and hinders catalysis. To overcome this problem, a selective binding of the functional groups to appropriate sites in the catalyst is pursued. An interaction of functional groups of the monomer with carefully placed complementary hydrogen-bonding motifs in the bidentate ligand of neutral Pd(II) catalysts is sought to favor olefin coordination over binding of the incoming monomers functional groups. In extension of this concept also to the polar groups of already incorporated monomer, a diversion of their binding away from chelating coordination blocking the active sites is aimed for. An alternative approach to resolve this problem - potentially also providing new copolymer microstructures - is a combination of ethylene insertion chain growth with free-radical growth of polar monomer segments. Monteil (Macromolecules 2011, 44, 3293) suggested that neutral Ni(II) salicylaldiminato complexes polymerize ethylene and methyl methacrylate (MMA) to (multi)block copolymers. Our preliminary studies confirm that an insertion chain growth of ethylene and radical polymerization of MMA occur simultaneously, and both reactions are interdependent. To unravel the mechanisms operative here and devise generic concepts to insertion/radical 'shuttling' polymerizations, polymerizations with (13C labeled) Ni-aryl and Ni-methyl precursors will be pursued, combined with polymer endgroup analysis. Further, the role of the metal in generating and scavenging radicals will be illuminated by studies of (salicylaldiminato)Ni(I) species prepared for this purpose. This comprises their reactivity under polymerization conditions as well as stoichiometric reactions with the active species of insertion chain growth.Stereocontrol by space-filling repulsive interactions, established for propylene, is not applicable here. We have devised an asymmetric substitution of moderate bulk at a P-donor adjacent to the bound olefin as a concept to control acrylate insertion. This serves as a starting point to develop stereoregular chain growth via remote rigid linkers. In further course, the aforementioned concepts of attractive interactions can come into play.