Samuel Kyeremateng - Effect of Hydrophilic Block-A Length Tuning on the Aggregation Behavior of α,ω-Perfluoroalkyl End-Capped ABA Triblock Copolymers in Water

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      Macromolecules, 2010, 43 (5), pp 2502-;2511


      The tremendous influence of hydrophilic block length tuning on   the  aggregation behavior of novel water-soluble triphilic   (i.e.,  hydrophilic, lipophilic, and fluorophilic)   α,ω-perfluoroalkyl end-capped  symmetric ABA triblock   copolymers is demonstrated. The hydrophilic A  and   lipophilic B blocks are comprised of poly(glycerol   monomethacrylate)  (PGMA) and poly(propylene oxide) (PPO),   respectively. The fluorophilic  component consists of two   “clicked” perfluoroalkyl segments (C9F19)   at the ends of the block copolymers. Two of the different block   copolymers synthesized, namely   F9-PGMA24-PPO27-PGMA24-F9  (PB1) and   F9-PGMA42-PPO27-PGMA42-F9  (PB2), differ only in the degree of polymerization of the   hydrophilic  PGMA blocks. Their critical micelle   concentrations in water are  determined from surface tension   measurements. The aggregation behavior  in aqueous medium   studied by 19F NMR spectroscopy reveals  that the   fluorocarbon component forms part of the micelle corona of   PB1,  while in PB2 it aggregates to form part of the core.   Furthermore, the  aggregation behavior studied in aqueous   medium by temperature-dependent 1H NMR spectroscopy   and DLS measurements showed that PB1 forms only spherical   micelles with hydrodynamic radius, Rh, of   18   nm in solution at all temperatures while PB2 forms mainly   aggregate of micelles with Rh of 40 nm at 25   °C. The aggregates disintegrate into compact single “flowerlike”   micelles with Rh of 17    nm at high temperatures. AFM and TEM investigations of the   structures  formed on solid supports after solvent   evaporation also confirm the  aggregation behavior of the   two block copolymers. The marked difference  in the   aggregation behavior is a result of the inability of the   shorter  PGMA blocks of PB1 to loop during micellization and   is explained based  on random coil statistics.

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