Tuning Nanostructure Morphology and Gold Nanoparticle “Locking” of Multi-Responsive Amphiphilic Diblock Copolymers † Paper No. 138 in a series on Water Soluble Polymers.

Reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to prepare multiresponsive, self-assembling amphiphilic poly[( N, N -dimethylaminoethyl methacrylate) x - b -( N -isopropylacrylamide) y ] (DMAEMA x - b -NIPAM y ). Controlling block lengths, solution pH, and NaCl concentration to elicit changes in the hydrophilic mass fraction resulted in specific morphological changes upon thermally induced assembly. At y = 102 (68 wt % DMAEMA), DMAEMA 165 - b -NIPAM 102 copolymers self-assemble into simple core−shell micelles (58 nm). Increasing y to 202 (48 wt % DMAEMA) leads to a mixture of spherical micelles (78 nm) and worm-like micelles ( D = 50−100 nm, L = 400−500 nm). Further increasing y to 435 (36 wt % DMAEMA) produces vesicular structures (179 nm). Significantly, reversible assembly of these nanostructures from the present stimuli-responsive diblock copolymers can be accomplished directly in aqueous media without the necessity of dialysis or manipulation with cosolvents. Additionally, the associated nanostructures can be shell cross-linked above the critical aggregation temperature via the in situ formation of gold nanoparticles yielding assemblies with long-term aqueous stability.