Atom transfer radical polymerization synthesis and association properties of amphiphilic pullulan copolymers grafted with poly(methyl methacrylate)

Amphiphilic copolymers of pullulan grafted with poly(methyl methacrylate) (PMMA) were synthesized by atom transfer radical polymerization under homogeneous mild conditions without using protecting group chemistry. The hydroxyl groups of pullulan were reacted with 2-bromoisobutyryl bromide to prepare pullulan macroinitiators with various degrees of substitution. Kinetic study showed that the polymerization was first order. The copolymers were characterized using (1)H NMR spectroscopy and gel permeation chromatography. The molecular weights of the grafted chains were controlled and polydispersities were low. Association properties in aqueous solution were studied using (1)H NMR spectroscopy, dynamic light scattering and transmission electron microscopy. Spherical nanoparticles with size and size distribution significantly affected by the number and length of the grafted chains were formed. Graft copolymers with a degree of substitution of 5.3% and length of PMMA grafted chains from 5 to 35 repeating units formed well-defined quite monodisperse spherical nanoparticles with hydrodynamic diameters in the range 20-40 nm. This means that nanoparticle size can be tuned by changing the length of the grafted chains for this degree of substitution. Less control of aggregate size was obtained for a degree of substitution of 1.0%. (C) 2010 Society of Chemical Industry