Search

Two graft copolymers comprising acrylic acid (AAc) and 2-methacryloylethyl acrylate (MEA) units as the backbone and either poly(N-isopropylacrylamide) (PNIPAAm) alone or both PNIPAAm and monomethoxypoly(ethylene glycol) (mPEG) as the grafts were synthesized. These copolymers in the aqueous phase (pH 5.0) underwent thermally induced self-assembly into micelles. For the copolymer containing PNIPAAm grafts only, extensive interactions between un-ionized AAc residues and PNIPAAm segments occurred, thereby rendering polymer backbones partially embedded within the hydrophobic cores of thermally induced micelles. This then led to bulk (core/shell) cross-linking of micelles upon radical polymerization of the MEA units within the micellar assemblies in the aqueous phase. By contrast, with mPEG being incorporated into the copolymer, association of the backbones with PNIPAAm is greatly retarded. As a result, three-layer onion-like polymeric micelles consisting of hydrophobic PNIPAAm cores surrounded by AAc-rich shel...

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 °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 conce...