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    Synthesis and Organization of Three-Arm-Star PIB-PEO Block Copolymers at the Air/Water Interface: Langmuir- and Langmuir-Blodgett Film Investigations

    Year: 2010

    Journal: Macromolecular Chemistry and Physics (2010), 211(2), 204-214, 20121205

    Authors: Rother, Marko; Barqawi, Haitham; Pfefferkorn, Dirk; Kressler, Joerg; Binder, Wolfgang H.

    Organizations: Faculty of Natural Sciences II (Chemistry and Physics), Institute of Chemistry, Martin Luther University Halle-Wittenberg, Lehrstuhl f. Makromolekulare Chemie, Halle, Germany, Faculty of Natural Sciences II (Chemistry and Physics), Institute of Chemistry, Martin Luther University Halle-Wittenberg, Lehrstuhl f. Physikalische Chemie der Polymere, Halle, Germany

    The synthesis of three-arm-star (PIB–PEO) block copolymers (BCPs) via azide/alkyne “click” reaction and their behavior at the air/water interface are reported. Starting from a three-arm-star allyl-telechelic PIB (1) prepared by living cationic polymerization, the three-arm-star PIB–(CH2N3)3 (2c) was generated via borane addition/oxidation PIB–(CH2OH)3, (2a) followed by reaction with CBr4/PPh3 furnishing PIB–(CH2Br)3 (2b) and then the PIB–(CH2N3)3 (2c) after reaction with trimethylsilyl-azide/tetrabutylammonium fluoride. The final three-arm-star (PIB–PEO) BCPs (4a, 4b) were then generated by azide/alkyne “click” reaction of the PIB–(CH2N3)3 (2c) with alkyne-telechelic PEOs (3a, 3b) in a biphasic water/toluene mixture, using copper(II) sulfate pentahydrate/sodium ascorbate as the Cu(I)-regenerative system and microwave irradiation. NMR spectroscopy and MALDI investigations proved the final structure of the three-arm-star PIB–PEO BCPs. Subsequent Langmuir- and Langmuir–Blodgett films investigations of 4a and 4b reveal the absence of a pancake-to-brush transition. Compared to PIB54–(PEO3–OCH3)34a, the collapse of PIB54–(PEO16–OCH3)34b occurs at higher surface pressures and lower mean molecular area values indicative of stronger anchoring of the PIB block to the air/water interface. Addition of iron-oxide nanoparticle (Rh = 83 Å) leads to a stabilization of the hydrophobic layer of 4a, thus shifting the collapse to higher surface pressures.