Synthesis, micelle formation, and bulk properties of poly(ethylene glycol)-b-poly(pentafluorostyrene)-g-polyhedral oligomeric silsesquioxane amphiphilic hybrid copolymers

The synthesis, micelle formation and bulk properties of semifluorlnated amphiphilic poly(ethylene glycol)-b-poly(pentafluorostyrene)-g-cubic polyhedral oligomeric silsesquioxane (PEG-b-PPFS-g-POSS) hybrid copolymers is reported. The synthesis of amphiphilic PEG-b-PPFS block copolymers are achieved using atom transfer radical polymerization (ATRP) at 100 ?C in trifluorotoluene using modified poly(ethylene glycol) as a macroinitiator. Subsequently, a proportion of the reactive para-F functionality on the pentafluorostyrene units was replaced with aminopropylisobutyl POSS through aromatic nucleophilic substitution reactions. The products were fully characterized by 1H-NMR and GPC. The products, PEG-b-PPFS and PEG-b-PPFS-g-POSS, were subsequently self-assembled in aqueous solutions to form micellar structures. The critical micelle concentrations (cmc) were estimated using two different techniques: fluorescence spectroscopy and dynamic light scattering (DLS). The cmc was found to decrease concomitantly with the number of POSS particles grafted per copolymer chain. The hydrodynamic particle sizes (Rh) of the micelles, calculated from DLS data, increase as the number of POSS molecules grafted per copolymer chain increases. For example, Rh increased from 60 nm for PEG-b-PPFS to 80 nm for PEG-b-PPFS-g-POSS25 (25 is the average number of POSS particles grafted copolymer chain). Static light scattering (SLS) data confirm that the formation of larger micelles by higher POSS containing copolymers results from higher aggregation numbers (A agg), caused by increased hydrophobicity. The Rg/R h values, where Rg is the radius of gyration calculated from SLS data, are consistent with a spherical particle model having a core-shell structure. Thermal characterization by differential scanning calorimetry (DSC) reveals that the grafted POSS acts as a plasticizer; the glass transition temperature (Tg) of the PPFS block in the copolymer decreases significantly with increasing POSS content. Finally, the rhombohedral crystal structure of POSS in PEG-b-PPFS-g-POSS was verified by wide angle X-ray diffraction measurements.