Iron and aluminum phosphido complexes for the sterocontrolled synthesis of biodegradable polymer brushes and stars

绿色化学是一套化学理想，推动许多化学家走向可持续和环保的操作。这些概念包括：(i)原子经济，理想情况下，放入反应容器的原子100%最终会进入产品；（ii）降低毒性，用可生物吸收的替代品交换有毒试剂；（iii）可再生原料，用可持续资源取代耗尽的石油基产品；（iv）催化，可以在不浪费化学计量试剂的情况下进行专门的转化。特别是，在生产塑料和聚合物时使用基于石油的不可再生资源，以及有关废物对环境的影响，都需要研究替代办法。聚乳酸（PLA）是一种具有商业意义的、无毒的、可生物降解的热塑性塑料，它很容易通过一种叫做丙交酯的化学物质的开环聚合生产出来。这种乳酸单体也是可再生的，因为它最终产生的乳酸来源于农业副产品的发酵。对聚乳酸的研究使其处于生物可降解聚合物研究的前沿，但其应用仍然局限于服装和包装行业。扩大聚乳酸的使用需要化学家改进和调整聚合物的性质。正如我们的左手和右手不能重叠一样，许多分子也具有典型的手性。通过控制这些手或立体异构体如何在聚合物链中结合在一起，我们可以改善聚合物的性能：随机排列产生粘性玻璃，交替排列产生白色固体，而期望的立体配合物形式的PLA提供增强的热性能。本课题设计了立体控制聚合丙交酯的新型催化剂。这些催化剂将以廉价的金属为基础，包括铁和钒，并由新型磷配体支撑。立体控制也将被整合到更大的聚合物结构中，包括类似刷子和星星的形状，以生产新的增值产品。这些新材料的生产将扩大环保生物可降解聚合物的应用，造福社会。

Green chemistry is a set of chemical ideals that drive many chemists towards sustainable and environmentally friendly operations. These concepts include: (i) atom economy, where ideally 100% of the atoms you put into a reaction vessel end up in the product, (ii) reduced toxicity, where toxic reagents are exchanged for bioassimilable alternatives, (iii) renewable feedstocks, replacing depleting petroleum-based products with sustainable resources, and (iv) catalysis, where specialized transformations can be performed without the wasteful use of stoichiometric reagents. In particular, the use of petroleum-based non-renewable resources in the production of plastics and polymers and the environmental impact of the associated waste necessitates research into alternatives. Poly(lactic acid), or PLA, is a commercially relevant, non-toxic and biodegradable thermoplastic which is readily produced through the ring-opening polymerization of a chemical called lactide. This lactide monomer is also renewable, as the lactate from which it is ultimately produced is derived from the fermentation of agricultural by-products. Research into PLA has placed it at the forefront of biodegradable polymer research, however applications remain limited to the clothing and packaging industries. Expanding the use of PLA requires chemists to improve and tune the properties of the polymer. Just as our left and right hands cannot be overlain, many molecules also have a characteristic handedness. By controlling how these hands, or stereoisomers, fit together in a polymer chain, we can improve polymer properties: a random arrangement gives a sticky glass, an alternating arrangement gives a white solid, while the desired stereocomplex form of PLA offers enhanced thermal properties. This project designs new catalysts for the stereocontrolled polymerization of lactide. These catalysts will be based on inexpensive metals including iron and vanadium supported by novel phosphorus ligands. Stereocontrol will also be incorporated into larger polymer architectures, including shapes resembling brushes and stars to produce new value-added products. Production of these new materials will expand the applications of environmentally friendly biodegradable polymers to the benefit of society.