Modification of the Co-assembly Behavior of Double-Hydrophilic Block Polyelectrolytes by Hydrophobic Terminal Groups: Ordered Nanostructures with Interpolyelectrolyte Complex Domains

We report here the influence of hydrophobic terminal groups from RAFT chain transfer agent 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl]­pentanoic acid on the co-assembly behavior of two oppositely charged double-hydrophilic block polyelectrolytes (DHBPs), poly­{[2-(methacryloyloxy)­ethyl]­trimethyl ammonium iodide}-b-poly­(N-isopropyl acrylamide) (QPDMAEMA-PNIPAm), with the dodecyl group at the end of the PNIPAm block, and poly­(acrylic acid)-b-poly­(N-isopropyl acrylamide) (PAA-PNIPAm). The co-assembly process was investigated using dynamic light scattering (DLS), differential scanning calorimetry (DSC), time-resolved small-angle X-ray scattering (SAXS), and cryo-transmission electron microscopy (TEM). The terminal dodecyl group of QPDMAEMA-PNIPAm induced hydrophobic association of PNIPAm coronas of QPDMAEMA-PNIPAm/PAA-PNIPAm core–corona particles into micrometer-sized aggregates. In ca. 2 s after mixing the DHBPs, the aggregates formed an ordered structure with constant distances (∼30 nm) between interpolyelectrolyte complex cores of the core–corona particles. This paper thus shows that a modification of double-hydrophilic block polyelectrolytes by low-molecular-weight hydrophobic terminal groups is a simple route for preparation of nanostructured networks of physically cross-linked nanoparticles with potential application as containers for encapsulation and delivery of multivalent ions.