Hierarchically Self-Assembled Amphiphilic Alternating Copolymer Brush Containing Side-Chain Cholesteryl Units

We synthesized a novel amphiphilic alternating copolymer brush (AACPB), poly{maleimide-g-poly[10-(cholesteryloxycarbonyl) decyl methacrylate]}-alt-(styrene-g-poly(ethylene oxide)) (P (MI-g-PCholMA)-alt-(St-g-PEO)), by copolymerization of maleimide-terminated poly[10-(cholesteryloxycarbonyl)decyl methacrylate] (MI-PCholMA) and styrene-terminated poly(ethylene oxide) (St-PEO). The thermal properties of the polymer brushes were investigated by thermogravimetric analysis and differential scanning calorimetry. After solvent and thermal annealing, the AACPB self-assembles into a hierarchically ordered nanostructure. One is the microphase-separated lamellar nanostructure with a 9.66 run scale. The other is the cholesteryl double-layer smectic A phase (SmA(d)) with a 5.46 nm scale. The order-disorder transition of the AACPB is associated with the SmA(d)-isotropic transition. It is the first report on the microphase separation of AACPBs. We can construct ordered nanostructures with a sub -10 nm length scale with AACPBs. After the doping of 0.2 equiv of LiCF3SO3, the d-spacing of the lamellar structure formed by the PCholMA(8)-alt-PEO23/LiCF3SO3 complex increases because the interaction between Li+ and oxygen atom makes the PEO chains more stretched. Such a structure offers lithium salt-doped PEO nanochannels which can act as pathways for the transport of lithium ion.