Self‐assembly of ABA triblock copolymers based on functionalized polydimethylsiloxane and polymethyloxazoline |
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| Authors: | Luke Theogarajan Hangsheng Li Karsten Busse Salil Desai Jörg Kressler Carmen Scholz |
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| Affiliation: | 1. 4123 Harold Frank Hall, University of California Santa Barbara, CA, USA;2. Naturwissenschaftliche Fakult?t II/Institut für Chemie, Martin‐Luther‐Universit?t Halle‐Wittenberg, Germany;3. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA;4. Department of Chemistry, University of Alabama in Huntsville, AL, USA |
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| Abstract: | This study describes the responsive behavior of modified amphiphilic ABA triblock copolymers of polymethyloxazoline‐block‐poly(methylhydrosiloxane‐co‐dimethylsiloxane)‐block‐polymethyloxazoline (PMOX‐b‐P(MHS‐co‐DMS)‐b‐PMOX) when subjected to compression on the water surface or to ions in the water bulk phase. The hydrophobic middle block was functionalized with spacers bearing methyl 2‐hydroxybenzoate (Bz) or 18‐crown‐6 ether (Ce) groups. The behavior at the air–water interface was studied by measuring surface pressure versus mean molecular area (π–mmA) isotherms, and atomic force microscopy (AFM) was employed to investigate the morphology of Langmuir–Blodgett (LB) films after transfer to solid supports. Ion‐responsive self‐assembly was followed using light microscopy and can be understood on a molecular level by employing 1H NMR spectroscopy. The π‐mmA isotherm of PMOX‐b‐P(MHS‐co‐DMS)‐b‐PMOX‐44Bz at the air–water interface had an extended pseudo‐plateau at a surface pressure of ca 22 mN m?1 reflecting the coil to loop transformation of the hydrophobic middle block which was absent for the crown ether‐functionalized triblock copolymer. AFM images of LB films of PMOX‐b‐P(MHS‐co‐DMS)‐b‐PMOX‐44Bz showed dewetting effects of the polymer film after transfer to a silicon wafer. LB films of PMOX‐b‐P(MHS‐co‐DMS)‐b‐PMOX‐8Ce formed surface micelles having a size of ca 50–100 nm on the solid support. The ion sensitivities of the crown ether‐derivatized copolymers in solution were investigated by exposing polymeric vesicles to potassium, sodium and magnesium ions. Exposure to K+ and Na+ led to vesicle rupture and the formation of micro‐tubular structures, while Mg2+ had no effect on the vesicular structures as confirmed using light microscopy. Specific interactions between the crown ether‐derivatized polymer and ions were further elucidated from 1H NMR experiments that indicated that K+ coordinated with the crown ether causing the dense packing to subside and leading to solubilization of the polymer in water. Copyright © 2010 Society of Chemical Industry |
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| Keywords: | polymethyloxazoline‐block‐poly(methylhydrosiloxane‐co‐dimethylsiloxane)‐block‐polymethyloxazoline self‐assembly atomic force microscopy (AFM) transmission electron microscopy (TEM) nuclear magnetic resonance (NMR) spectroscopy |
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