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 coassembly 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 (similar to 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.

Automated summary

This study investigated the influence of hydrophobic terminal groups on the coassembly behavior of two oppositely charged double-hydrophilic block polyelectrolytes, showing that the terminal groups induced the formation of ordered aggregates. Modification of DHBPs with low-molecular-weight hydrophobic terminal groups is a simple route for preparing nanostructured networks of physically cross-linked nanoparticles with potential applications in encapsulation and delivery of multivalent ions.