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

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)(3) 4a, the collapse of PIB54-(PEO16-OCH3)(3) 4b 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 (R-h = 83 angstrom) leads to a stabilization of the hydrophobic layer of 4a, thus shifting the collapse to higher surface pressures.