Microphase Separation and High Ionic Conductivity at High Temperatures of Lithium Salt-Doped Amphiphilic Alternating Copolymer Brush with Rigid Side Chains

An amphiphilic alternating copolymer brush (AACPB), poly{(styrene-g-poly(ethylene oxide))-alt-(maleimid e-g-p oly{2,5-bis[4-methoxyphenyl)oxycarbonyn styrene})}(P{(St-g-PEO)-alt-(MI-g-PMPCS)}), was synthesized by alternating copolymerization of styreneterminated poly(ethylene oxide) (St-PEO) and maleimide-terminated poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (MI-PMPCS) macromonomers using the grafting through strategy. H-1 NMR and gel permeation chromatography coupled with multiangle laser light scattering were used to determine the molecular characteristics of AACPBs. Although these AACPBs cannot microphase separate with thermal and solvent annealing methods, they can form lamellar structures by doping a lithium salt. This is a first report on lithium salt-induced microphase separation of AACPBs, and the lithium salt-doped AACPBs can serve as solid electrolytes for the transport of lithium ion. For the same AACPB, the ionic conductivity (sigma) increases with increasing doping ratio. In addition, sigma values of different AACPBs with the same doping ratio become higher for shorter PMPCS side chains. The sigma value of the lithium salt-doped AACPB increases with increasing temperature in the range of 25-240 degrees C, and sigma is 1.79 x 10(-4) S/cm at 240 degrees C. The relatively high sigma values of the lithium-doped AACPBs at high temperatures benefit from the rigid PMPCS side chain and the AACPB architecture. The lithium salt-doped AACPBs have the potential to serve as solid electrolytes in high-temperature lithium ion batteries.