Preparation and characterization of surfactant-free nanoparticles composed of stereoregular poly(methyl methacrylate)s.

Surfactant-free nanoparticles composed of isotactic (it), syndiotactic (st), and atactic (at) poly(methyl methacrylate)s (PMMAs) with fairly narrow size distributions were prepared by adding water into PMMA solutions of tetrahydrofuran (THF), and subsequently evaporating THF. Particle sizes and morphologies from obtained nanoparticles were characterized by scanning electron microscopy and dynamic light scattering. The particle size was unexpectedly dependent on PMMA stereoregularity. Under the same preparation conditions, the at-PMMA nanoparticle showed the largest size, while the it-PMMA showed the smallest. The particle size generally increased by increasing the initial PMMA concentration and the THF/water volume ratio. Attenuated total reflection infrared and wide-angle X-ray diffraction measurements revealed it- and st-PMMAs formed characteristic helical structures in nanoparticles. Based on these observations, a possible mechanism for the formation of particles composed of stereoregular PMMAs was proposed. As a novel finding, we show herein that the formation of helical nanostructures during particle preparation results in a decrease in particle size.