Synthesis and Reactions of Strained Molecules and Polymers

加州大学欧文分校化学系的Kenneth Shea教授因研究应变分子和聚合物的合成和反应而得到有机合成计划的支持。烷基硼烷引发了二甲基亚砜的聚合，形成了具有极窄多分散指数的完美线性聚亚甲基。调整叶立德与烷基硼烷的初始比例可以控制生成的聚亚甲基的分子量，而多同系烷基硼烷碳-硼键的化学转化允许引入各种末端官能团。将这种多同系物化学扩展到更复杂的烷基硼烷引发剂，可以获得新型的聚亚甲基结构，包括星形、梳状和超支化聚合物。该化学也可用于形成嵌段共聚物，该嵌段共聚物将聚亚甲基与不相容的聚硅氧烷和聚乙二醇共价连接。发展对聚合物的形成和结构的控制是聚合物化学科学和技术领域的一个中心问题。聚合物是由小分子衍生的化学连接的重复单元组成的大分子。Kenneth Shea教授利用了一类不寻常的形成聚合物的化学反应，在这种反应中，单个碳原子一次一个地添加到不断增长的聚合物链中。这种化学提供了合成一系列三维聚合物结构的途径，包括圆形、梳状和星形材料，从而可以确定这种不寻常的结构基元对聚合物材料的内在和整体性质的影响。其他研究涉及嵌段共聚物(两种或两种以上相互化学连接的不同聚合物)的形成，其中连接的聚合物显示出截然不同的性质。这种结合预计会产生不寻常的物理和化学性质，包括形成可以随着环境的变化而改变其形状和/或性质的材料。

Professor Kenneth Shea, of the Department of Chemistry at the University of California, Irvine, is supported by the Organic Synthesis Program for his studies of the synthesis and reactions of strained molecules and polymers. Alkyl boranes initiate the polymerization of dimethylsulfoxonium methylide, resulting in the formation of perfectly linear polymethylene with an extremely narrow polydispersity index. Adjustment of the initial ratio of ylide to alkyl borane permits control of the molecular weight of the resulting polymethylene, while chemical transformations of the carbon-boron bonds of polyhomologated alkyl boranes allow the introduction of a variety of terminal functionalities. Extension of this polyhomologation chemistry to more complex alkyl borane initiators affords access to novel polymethylene architectures, including star, comb, and hyperbranched polymers. The chemistry may also be adapted to the formation of block copolymers which covalently link polymethylene with the incompatible polysiloxanes and polyethylene glycols. Development of control over the formation and structures of polymers, macromolecules comprised of chemically-linked repeating units derived from smaller molecules, is a central issue in the scientifically and technologically vital area of polymer chemistry. Professor Kenneth Shea exploits an unusual class of polymer-forming chemical reactions, wherein individual carbon atoms are added to a growing polymer chain one at a time. This chemistry affords synthetic access to a range of three-dimensional polymer structures, including circular-, comb-, and star-shaped materials, and will thereby permit the determination of the effects of such unusual structural motifs on the intrinsic and bulk properties of polymeric materials. Additional studies address the formation of block copolymers (two or more distinct polymers chemically linked to one-another) in which the linked polymers display drastically different properties. Unusual physical and chemical properties are expected to arise from such unions, including the formation of materials which can change their shapes and/or properties as a function of their environment.