Thermally responsive interactions between the PEG and PNIPAAm grafts attached to the PAAc backbone and the corresponding structural changes of polymeric micelles in water

Graft copolymers comprising poly(acrylic acid) (PAAc) as the backbone and poly(N-isopropylacrylamide) (PNIPAAm) and monomethoxy poly(ethylene glycol) (mPEG) as the grafts were prepared and characterized. These copolymers with the AAc residues in the negatively charged state underwent self-assembling into large polymeric aggregates in water in the range 32-35 degrees C due to the formation of the multicore structure (comprising several solidlike hydrophobic PNIPAAm cores surrounded by the liquidlike interfacial layers) and the intercore PEG connections. These rather labile intercore PEG connections were partially destroyed due to the continual dehydration and solidification of the liquidlike interfacial layers with increasing temperature, thereby leading to fragmentation of the original aggregates into smaller particles with the more distinct core/shell structure. The final particle size was virtually governed by the structure of the hydrophobic PNIPAAm microdomains in response to the effects of the PNIPAAm concentration and temperature on the intercore PEG connections.