pH- and thermo-responsive solution behavior of amphiphilic, linear triblock terpolymers

We report on the synthesis and self-assembly in aqueous media, of novel amphiphilic double-responsive (temperature and pH) linear triblock terpolymers having the chain structure poly(n-butyl acrylate-b-N-iso-propylacrylamide-b-2-(dimethylamino) ethyl acrylate) (PnBA-b-PNIPAM-PDMAEA). The terpolymers were synthesized by sequential RAFT polymerization and molecularly characterized by SEC, H-1 NMR and FT-IR spectroscopy. The tertiary amine groups of the PDMAEA block were quaternized and converted to strong cationic block polyelectrolytes. Light scattering along with electron and atomic force microscopy observations, revealed that PnBA-b-PNIPAM-b-PDMAEA terpolymers form micelles with PnBA cores and mixed coronas in aqueous solutions. The micelles present strong tendency for intermicellar aggregation, probably a result of corona-corona interactions through hydrogen bonding. Increase in temperature above the LCST of PNIPAM results to further aggregation and decrease in the overall size of the polymeric aggregates, due to shrinking of the PNIPAM blocks. The quaternized terpolymers have been found to form spherical micelles with lower intermicellar aggregation phenomena.