On-Off Switching of Dynamically Controllable Self-Assembly Formation of Double-Responsive Block Copolymers with Tunable LCSTs

We report here a reversible self-assembly formation system using block copolymers with thermo-tunable properties. A series of double-responsive block copolymers, poly(N-isopropylacrylamide (NIPAAm))-block-poly(NIPAAm-co-N-(isobutoxymethyl) acrylamide (BMAAm)) with two lower critical solution temperatures were synthesized by one-pot atom transfer radical polymerization via sequential monomer addition. When dissolved in aqueous solution at room temperature, the block copolymers remained unimeric. Upon heating above room temperature, the block copolymers self-assembled into micellar structures. The micelle formation temperature and the resulting diameter were controlled by varying the BMAAm content. 1 H Nuclear Magnetic Resonance, dynamic light scattering, field-emission scanning electron microscopy, and fluorescence spectra revealed the presence of a monodisperse nanoassembly, and demonstrated the assembly formation/inversion process was fully reversible. Moreover, a model hydrophobic molecule, pyrene, was successfully loaded into the micelle core by including pyrene in the original polymer solution. Further heating resulted in mesoscopic micelle aggregation and precipitation. This dual micelle and aggregation system will find utility in drug delivery applications as a thermal trigger permits both aqueous loading of hydrophobic drugs and their subsequent release. VC 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4393-4399, 2010