The polymerization of acrylonitrile in miniemulsions: "Crumpled latex particles" or polymer nanocrystals

Stable dispersions of polyacrylonitrile (PAN) nanoparticles in the size ran ge between 100 nm < d < 180 nm were made by polymerization in miniemulsion and characterized by dynamic light scattering, transmission electron micros copy (TEM), and wide angle X-ray scattering (WAXS). Due to the insolubility of the polymer in its monomer, such particles are not accessible by classi cal emulsion polymerization. The pure PAN particles are composed of ca. 10 nm large polymer nanocrystals, i.e., the formed polymer precipitates and cr ystallizes direct after formation. As a consequence, the final latexes do n ot adopt spherical shape, but show a well defined, narrowly distributed bou lder-like phenotype which is called "crumpled latexes". Copolymerization wi th styrene results in a continuous transition between the crumpled and a sm ooth spherical morphology, which is again related to a decreased degree of crystallinity.