Reversible "Self-Locked" Micelles from a Zwitterion-Containing Triblock Copolymer

The versatility of aqueous reversible addition-fragmentation chain transfer (RAFT) process utilizing a trithiocarbonate chain transfer agent and monomers with zwitterionic, anionic, and neutral functionability that can be polymerized in water without protecting groups was demonstrated. The molecular weights and polydispersities of the co-polymer were determined using a Wyatt Technologies aqueous size exclusion chromatography (ASEC). The formation of 'self-locked' micelles is induced by first lowering solution pH below the pK a of the AMBA block at a salt concentration, removing the salt by dialysis. The reversible cross-links from the interaction of the zwitterionic groups are readily broken by the addition of electrolyte, resulting in a micelle disassembly into unimers. The cross-linking method for forming polymeric micelles from a well-defined ABC triblock polymer synthesized in water does not require the addition of an external cross-linking agent.