Interfacial Structure of Poly(methylmethacrylate) in Contact with Tetrahydrofuran-Water Mixtures

Polymer nanoparticles of controlled size and narrow polydispersity are highly desirable in biomedical applications. Solvent-shifting is one of the promising methods to produce nanoparticles free of impurities, which involves the addition of a non-solvent to a pre-synthesized polymer in solution for precipitating nanoparticles. The mechanism by which the particles are formed is not understood, particularly the initial nucleation process during which the polymer chain undergoes conformational changes. In the present study, we investigate the coil-to globule transition induced by water (non-solvent) addition to poly(methylmethacrylate) (PMMA) solution in Tetrahydrofuran (THF). Contrary to 2-step coil-to-globule transition in dilute solution induced by temperature-shifting, we observe the formation of intermediate multi-chain aggregates (lifetime ~ days to months) before complete collapse of the chains into nanoparticles. To understand this, we probe the interface between PMMA thin film and THF-water mixtures using interface-sensitive sum frequency generation spectroscopy. A model explaining the formation of these intermediate aggregates will be discussed along with the interfacial structure.