Prof. Mitchell A. Winnik 1.) "pH-responsive polymer nanoparticles designed for environmentally compliant coatings" 2.) "Crystallization-driven self-assembly of block copolymer micelles"

I will provide an overview of two quite different topics in the area of soft materials.

The first describes the synthesis and film-forming properties of two-component pH-responsive latex nanoparticles consisting of a high molecular weight polymer core and a carboxyl-rich oligomeric shell. These particles undergo a reversible transformation from a core-shell morphology at basic pH to a uniform (miscible polymer blend) morphology at acidic pH. Films formed from latex neutralized by ammonia have retarded coalescence because of the water-swollen shell around each particle. Upon drying, the ammonia evaporates. The carboxyl groups are protonated, and in this form, the oligomer promotes coalescence and polymer diffusion in the film. This approach may help overcome a longstanding problem with “open time” in waterborne coatings.

The second topic involves micelle formation in selective solvents by block copolymers in which polyferrocenylsilane (PFS) is the core-forming block. Unlike many other block copolymers, these polymers form long (up to 10 μm), thin (10 to 20 nm) rigid rod micelles, a process that we believe is associated with the semicrystalline nature of the PFS core. Sonicated micelles form small crystallite fragments that can be used to seed the growth of longer micelles when additional polymer is added to the solution. In this way one can get micelle samples very uniform in length. Recently we have begun experiments to measure the kinetics of micelle growth in supersaturated solutions of the unimer. Micelle growth appears to take place on two time scales, and interpreting the fast and slow steps remains a challenge. I would welcome ideas from the audience about how one might explain this unexpected result.