ИСТИНА

Controlled self/co-assembly of multicomponent polymer systems into structures of defined morphology is an important field of macromolecular research, especially regarding sequential switching of micellar structures via stimuli-sensitive polymer blocks. An attractive and straightforward way to generate micellar structures is co-assembly of oppositely charged polyelectrolytes. As a model system, the spontaneous formation of an interpolyelectrolyte complex formed between a linear diblock copolymer poly(vinyl sulfonate)31-b-poly(N-isopropyl acrylamide)27 (PVS31-b-PNIPAM27) and a star-shaped heteroarm quaternized polymer made of poly(ethylene oxide)114-(poly(2-(dimethylaino)ethyl methacrylate)17)4 (PEO114-(qPDMAEMA17)4) was investigated. Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) studies were performed with aqueous 0.3 M NaCl solutions to ensure dynamic exchange of the polyions in the system. The scattering results indicate that colloidally stable micellar interpolyelectrolyte complexes (IPECs) are formed showing different hydrodynamic radii Rh and aggregation numbers at temperatures below and above the lower critical solution temperature (LCST) of PNIPAM (= 32C). This is explained with the partial dehydration of PNIPAM above its LCST and consequent agregation processes caused by hydrophobic interactions. Further X-ray scattering experiments provide an indication of structural changes of the micellar complexes showing reversibility upon crossing the LCST. Results of SAXS measurements performed at 60C suggest the formation of spherical particles. We propose an onion-like micellar structure with collapsed PNIPAM chains and IPEC in the core and the shell, surrounded by a corona of soluble PEO chains. At 20C, PEO as well as PNIPAM are both water-soluble suggesting the formation of a core-corona structure with the insoluble IPEC domain surrounded by a mixed PEO/PNIPAM corona.