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

摘要

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 (R_h = 83 Å) leads to a stabilization of the hydrophobic layer of 4a, thus shifting the collapse to higher surface pressures.