Synthesis of Various Block Copolymers via Precision Polymerizations with Application to Nano-Organizations

• Published in: KOBUNSHI RONBUNSHU Vol. 69; no. 10; pp. 567 - 579
• Main Author: SUGIHARA, Shinji
• Format: Journal Article
• Language: Japanese
• Published: The Society of Polymer Science, Japan 01.10.2012
• Subjects: Atom Transfer Radical Polymerization; Block Copolymer; Dispersion Polymerization; Latex; Living Cationic Polymerization; Micelle; Nano-Organization; Reversible Addition Fragmentation Chain Transfer; Self-Assembly; Vesicle
• ISSN: 0386-2186; 1881-5685
• DOI: 10.1295/koron.69.567

This comprehensive paper reviews recent topics which are related to the “Synthesis of Various Block Copolymers via Precision Polymerizations with Application to Nano-Organizations” of our research group. The recent development of precision polymerization has provided us with versatile tools for the synthesis of a wide range of functional block copolymers with well-defined structures. The molecular dimensions influence the self-assemblies and dictate their products, such as micelle, nanocage, and vesicle. Thus, we have prepared appropriate block copolymers for such nano-organizations without regard to polymerization fashion. Firstly, we describe the metal-free living cationic polymerization for vinyl ethers using HCl·Et2O without a complex metal catalyst. This allowed us to prepare the biocompatible/biodegradable block copolymer, polyvinyl alcohol-b-poly(ε-caprolactone). Secondly, the transformation of living cationic vinyl polymerization to reversible addition fragmentation chain transfer (RAFT) polymerization mediated by a carboxylic RAFT agent was investigated in order to prepare the novel block copolymers with both vinyl ether and a different block. The living cationic polymerization is initiated from a proton derived from the carboxylic RAFT agent, then, the RAFT group as a counteranion is recovered to propagating carbocation, followed by the RAFT polymerization. Using the transformation process, we prepared novel double thermoresponsive diblock copolymers, which formed micelles in water within a given temperature range. Thirdly, as an example of the robust nano-organization, shell cross-linked (SCL) micelles were prepared via either such a living cationic vinyl polymerization or atom transfer radical polymerization. In particular, if the target degree of cross-linking is sufficiently low, SCL nanocages can be obtained. For soft nanocapsules like the nanocage, we next investigated the RAFT dispersion polymerization. Macromolecular amphiphiles are known to form a wide range of nanostructures such as spheres, worms, and vesicles in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dilute copolymer solutions (<1%). We show that diblock copolymer self-assembly is precisely controlled by sequential reorganization during in situ polymerization in concentrated aqueous solutions. The final particle morphology is controlled not only by the block ratio but also by the total solids concentration. The RAFT dispersion polymerization was applied to the synthesis of anisotropic particles, namely lumpy rods. In this review, these four subjects were highlighted.