ATRP synthesis and association properties of thermo responsive anionic block copolymers

Thermosensitive anionic block copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and N-isopropylacrylamide (NIPAAM) with different block lengths were prepared by atom transfer radical polymerization (ATRP). Controlled polymerization was achieved by using ethyl 2-chloropropionate (ECP) as initiator and CuCl/CuCl2/tris(2-dimethylaminoethyl)amine (Me6TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 °C. Blocks lengths ranging from 36 to 98 repeating units were obtained. The association properties in aqueous solutions at different NaCl ionic strengths were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy and energy-filtered transmission electron microscopy. The block copolymers with a higher pNIPAAM/pAMPS ratio formed spherical core-shell type micelles independently of the ionic strength. The block copolymers with lower pNIPAAM/pAMPS ratio formed core-shell type micelles at high ionic strength. Larger particles were observed at low ionic strength which could be due to the formation of vesicles or compound micelles/micellar clusters.