Insertion polymerization of electron-deficient vinyl monomers

乙烯和丙烯的催化聚合是研究最充分的化学反应之一。与此形成鲜明对比的是，缺电子极性取代的乙烯基单体的插入聚合是一个长期存在的挑战。直到最近，乙烯与甚至包括丙烯酸的一系列单体的线性共聚才得以实现。在第一个供资期内，获得了控制插入链增长和催化剂失活的因素的全面情况。催化剂的设计是先进的，新的聚合物材料的发展。我们现在专注于克服极性乙烯基单体的插入（共）聚合的固有局限性。游离单体的官能团的配位，特别是通过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。为了克服这个问题，寻求官能团与催化剂中的适当位点的选择性结合。寻求单体的官能团与中性Pd（II）催化剂的双齿配体中小心放置的互补氢键基序的相互作用，以有利于烯烃配位超过引入单体官能团的结合。在扩展这一概念也已纳入单体的极性基团，其结合偏离螯合配位阻断活性位点的目的。解决这个问题的替代方法-也可能提供新的共聚物微结构-是乙烯插入链增长与极性单体链段的自由基增长的组合。Monteil（Macromolecules 2011，44，3293）提出中性Ni（II）水杨醛亚胺络合物将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，乙烯的插入链增长和MMA的自由基聚合同时发生，这两个反应是相互依赖的。为了解开这里的机制和设计通用概念插入/自由基的“穿梭”聚合，聚合（13 C标记）Ni-芳基和Ni-甲基前体将追求，结合聚合物端基分析。此外，金属在产生和清除自由基的作用将照亮为此目的制备的（水杨醛亚胺）镍（I）物种的研究。这包括它们在聚合条件下的反应性以及与插入链增长的活性物种的化学计量反应。通过空间填充排斥相互作用建立的丙烯的立体控制在这里不适用。我们已经设计了一个不对称取代的适度散装在P-供体相邻的绑定烯烃作为一个概念，以控制丙烯酸酯插入。这作为通过远程刚性连接体发展有规立构链生长的起点。在进一步的过程中，上述有吸引力的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.