Atom Transfer Reactions: Implications for Polymerization Catalysis

Robert M. Waymouth博士，斯坦福大学化学系，受到化学系无机、生物无机和有机金属化学项目的支持，致力于开发Ti（III）氧化态下明确定义的钛配合物的化学，研究在非极性介质中介导Ti（III）和Ti（IV）可逆相互转化的原子转移反应。并开发基于钛配合物的新型催化体系，在催化过程中改变氧化态。这些研究是针对苯乙烯的共聚催化剂，以及为苯乙烯和非共轭烯烃的嵌段共聚物的生产开发新的催化剂系统。对苯乙烯双极性聚合的机理研究将集中在明确定义的苯乙烯聚合前驱体的反应性上。将进行苯乙烯和乙烯均聚实验和苯乙烯/乙烯共聚实验，以测试Ti（III）和Ti（IV）配合物对苯乙烯和乙烯聚合活性的能力。钛配合物与稳定的氮氧化物如2,2,6,6-四甲基哌啶- n-氧（TEMPO）的配位化学将作为在非极性溶剂中可逆互转化Ti（III）和Ti（IV）的策略进行。Ti-TEMPO配合物的合成和ti -氮氧化物键的键能将通过热裂解和氮氧化物交换平衡进行研究。研究钛配合物与其他金属卤化物之间原子转移平衡的动力学和热力学，为金属卤素键能量学提供基础信息。这些研究将指导选择合适的原子转移氧化还原伙伴来介导Ti（III）和Ti（IV）配合物的相互转化。聚烯烃和聚苯乙烯是两类重要的聚合物。这项研究旨在开发一种催化剂系统，可以产生既含有聚烯烃又含有聚苯乙烯碎片的聚合物。如果可以控制每个单独组分的组成和“块”的大小，这种“块共聚物”的性质可以被精确地设计。在这个项目中，将开发新的钛催化剂，当钛带3+电荷时可以聚合苯乙烯，当钛带4+电荷时可以聚合烯烃。通过改变金属电荷，可以控制嵌段共聚物的组成。

Dr. Robert M. Waymouth, Chemistry Department, Stanford University, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division to develop the chemistry of well-defined titanium complexes in the Ti(III) oxidation state, to investigate atom transfer reactions that mediate the reversible interconversion of Ti(III) and Ti(IV)in non-polar media, and to develop new catalytic systems based on titanium complexes that change oxidation state during catalysis. These studies are directed at catalysts for the syndiospecific polymerization of styrene as well as the development of new catalyst systems for the production of block copolymers of styrene and non-conjugated olefins. Mechanistic studies of syndiospecific styrene polymerization will focus on the reactivity of well defined Ti(III) precursors for styrene polymerization. Styrene and ethylene homopolymerization experiments and styrene/ethylene copolymerization experiments will be carried out to test the competence of both Ti(III) and Ti(IV) complexes for styrene and ethylene polymerization activity. The coordination chemistry of titanium complexes with stable nitroxides such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) will be carried out as a strategy for reversibly interconverting Ti(III) and Ti(IV) in non-polar solvents. The synthesis of Ti-TEMPO complexes and the bond energies of the Ti-nitroxide bonds will be investigated by thermolysis and nitroxide exchange equilibria. The kinetics and thermodynamics of atom-transfer equilibria between titanium complexes and other metal halides will be investigated to provide fundamental information on metal-halogen bond energetics. These studies will guide the choice of appropriate atom-transfer redox partners to mediate the interconversion of Ti(III) and Ti(IV) complexes. Polyolefins and polystyrenes are two important classes of polymers. This research seeks to develop a catalyst system that can produce a polymer that contains both polyolefin and polystyrene fragments. The properties of such "block co-polymers" can be precisely engineered if the composition and the size of the "blocks" of each individual component can be controlled. In this project, new titanium catalysts that will polymerize styrene when the titanium has a 3+ charge and olefins when it bears a 4+ charge will be developed. By altering the metal charge the composition of the block copolymer can be controlled.