A Zwitterionic ABC Triblock Copolymer That Forms a “Trinity” of Micellar Aggregates in Aqueous Solution
journal contributionposted on 21.09.2004, 00:00 by Yuanli Cai, Steven P. Armes
A PEO-based macroinitiator was used to first polymerize 2-(diethylamino)ethyl methacrylate (DEA) and then 2-hydroxyethyl methacrylate (HEMA) in a one-pot synthesis via ATRP in methanol at 20 °C. The resulting PEO−PDEA−PHEMA triblock copolymer precursors were successfully converted into the corresponding PEO−PDEA−PSEMA zwitterionic triblock copolymers by esterification of the hydroxy groups on the HEMA block using excess succinic anhydride in pyridine under mild conditions. A “trinity” of micellar aggregates was formed by these PEO−PDEA−PSEMA triblock copolymers in aqueous solution simply by adjusting the solution pH at ambient temperature. The driving forces for forming these three types of micelles were hydrogen-bonding, interpolyelectrolyte complexation, and hydrophobic interactions, respectively. The hydrogen-bonded PSEMA/PEO-core micelles that were formed at low pH were disrupted at higher temperatures or by addition of methanol, leading to PSEMA-core aggregates. The PSEMA/PDEA interpolyelectrolyte micelles formed at around the IEP were very sensitive to the ionic strength of the aqueous solution. Dilution of these solutions resulted in swollen micelles, and eventually dissociation occurred. As far as we are aware, the rich aqueous solution behavior of this new class of ABC triblock copolymers is unprecedented since, for the first time, three types of micelles are formed in aqueous solution by a single-component system.