Synthesis and Post-functionalization of Well-defined Star Polymers via 'Double' Click Chemistry

摘要

Star polymers have attracted a lot of research interests due to their unique solution properties in particular their relationship between arm number, arm molecular weight and solvent viscosity. Star polymers can be seen as singular well-defined and structurally complex nanoparticles. In general well-defined star polymers have been prepared via two different routes; arm first approach or core first approach. In the core first approach, the synthesis of a suitable macro- initiator bearing a defined number of initiating groups is used to obtain star polymers. The approach was initially demonstrated using ionic polymerization techniques which are ideally suited to this star syntheses procedure as bimolecular termination (especially coupling) is not present, and therefore star-star coupling by-products are not produced. With the later discovery of living radical techniques, all three main living radical polymerization have been exploited to make multi-arm star polymers using this approach. However all these mechanisms suffer from radical intermediate termination reactions and therefore the optimization of the reaction conditions to minimize these becomes an important consideration for generating narrow polydispersities. In the unique case of RAFT polymerization, the star- star coupling problem can be addressed in a limited fashion by using a Z-group approach rather than a R-group approach to arm growth.