Diblock copolymers, micelles, and shell-crosslinked nanoparticles containing poly(4-fluorostyrene): Tools for detailed analyses of nanostructured materials

Amphiphilic core-shell nanostructures containing F-19 stable isotopic label s located regioselectively within the core domain were prepared by a combin ation of atom transfer radical polymerization (ATRP), supramolecular assemb ly, and condensation-based crosslinking. Homopolymers and diblock copolymer s containing 4-fluorostyrene and methyl acrylate were prepared by ATRP, hyd rolyzed, assembled into micelles, and converted into shell-crosslinked nano particles (SCKs) by covalent stabilization of the acrylic acid residues in the shell. The ATRP-based polymerizations, producing the homopolymers and d iblock copolymers, were initiated by (1-bromoethyl)benzene in the presence of CuBr metal and employed N,N,N',N",N"-pentamethyldiethylenetriamine as th e coordinating ligand for controlled polymerizations at 75-90 degreesC for 1-3 h. Number-average molecular weights ranged from 2000 to 60,000 Da, and molecular weight distributions, generally less than 1.1 and 1.2, were achie ved for the homopolymers and diblock copolymers, respectively. Methyl acryl ate conversions as high as 70% were possible, without observable chain-chai n coupling reactions or molecular weight distribution broadening, when brom oalkyl-terminated poly(4-fluorostyrene) was used as the macroinitiator. Pol y(4-fluorostyrene), incorporated as the second segment in the diblock copol ymer synthesis, was initiated from a bromoalkyl-terminated poly(methyl acry late) macroinitiator. After hydrolysis of the poly(methyl acrylate) block s egments, micelles were formed from the resulting amphiphilic block copolyme rs in aqueous solutions and were then stabilized by covalent intramicellar crosslinking throughout the poly(acrylic acid) shells to yield SCKs. The SC K nanostructures on solid substrates were visualized by atomic force micros copy and transmission electron microscopy. Dynamic light scattering was use d to probe the effects of crosslinking on the resulting hydrodynamic diamet ers of nanoparticles in aqueous and buffered solutions. The presence of flu orine atoms in the diblock copolymers and resulting SCK nanostructures allo wed for characterization by F-19 NMR in addition to H-1 NMR, C-13 NMR, and IR spectroscopy. (C) 2001 John Wiley & Sons, Inc.