Poly(N-isopropyl acrylamide)-block-poly(n-butyl acrylate) thermoresponsive amphiphilic copolymers: Synthesis, characterization and self-assembly behavior in aqueous solutions

Abstract

We report on the synthesis of poly(N-isopropyl acrylamide)-block-poly(n-butyl acrylate) (PNIPAm-b-PnBA) amphiphilic block copolymers and their temperature-responsive self-assembly behavior in aqueous solution. Well-defined PNIPAm-b-PnBA copolymers have been synthesized by a two-step RAFT polymerization scheme. The self-assembly behavior was studied by means of static and dynamic light scattering, 1H NMR and fluorescence spectroscopy and transmission electron microscopy. The results show that already below the lower critical solution temperature (LCST) of PNIPAm, association of the PNIPAm blocks with hydrophobic dodecyl end groups of the charge transfer agent leads to the formation of loose aggregates of PNIPAm-b-PnBA micelles, the size and density of which increase with the increasing length of the PNIPAm block. The collapse of the PNIPAm blocks above the LCST leads to the decrease of the aggregates’ size and the increase of their density, but the collapsed PNIPAm chains do not allow for interpenetration of the micellar shells and no further aggregation occurs.