Effect of Monomer Solubility on the Evolution of CopolymerMorphology during Polymerization-Induced Self-Assembly in AqueousSolution

摘要

Polymerization-induced self-assembly (PISA) has become a widely used technique for the rational design of diblock copolymer nano-objects in concentrated aqueous solution. Depending on the specific PISA formulation, reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization typically provides straightforward access to either spheres, worms, or vesicles. In contrast, RAFT aqueous emulsion polymerization formulations often lead to just kinetically-trapped spheres. This limitation is currently not understood, and only a few empirical exceptions have been reported in the literature. In the present work, the effect of monomer solubility on copolymer morphology is explored for an aqueous PISA formulation. Using 2-hydroxybutyl methacrylate (aqueous solubility = 20 g dm^–3 at 70 °C) instead of benzyl methacrylate (0.40 g dm^–3 at 70 °C) for the core-forming block allows access to an unusual “monkey nut” copolymer morphology over a relatively narrow range of target degrees of polymerization when using a poly(methacrylic acid) RAFT agent at pH 5. These new anisotropic nanoparticles havebeen characterized by transmission electron microscopy, dynamic lightscattering, aqueous electrophoresis, shear-induced polarized lightimaging (SIPLI), and small-angle X-ray scattering.