Layer-by-layer assembly of pH-responsive, compositionally controlled (co)polyelectrolytes synthesized via RAFT

Homo- and block copolyelectrolytes that have well-defined structures and are responsive to pH were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization and employed to produce layer-by-layer (LBL) films. Acrylamido monomers with carboxylate, sulfonate, and amine functionality were utilized to provide both strong and weak homopolyelectrolytes and mixed strong/weak copolyelectrolyte systems. Multilayer films were prepared under specified conditions of pH and ionic strength and analyzed via atomic force microscopy and ellipsometry to study the effects of changes in the local molecular environment on film morphologies. The pH responsiveness and integrity of the multilayer assemblies were investigated by exposing films to solutions of varying pH in a fluid cell and performing in situ AFM analysis. The multilayer dimensions, morphology, and integrity were found to depend on the molecular architecture of the polyelectrolytes, with changes in segmental type and repeating unit distribution producing dramatic differences in film characteristics. These results suggest the possibility of producing LBL assemblies of precisely controlled dimensions and properties by specifically tailoring copolymer structure. To our knowledge, this is the first report of LBL assembly of RAFT-synthesized homo- and copolyelectrolyte multilayer complexes.