Synthesis, structure, and ionic conductivity of self-assembled amphiphilic poly(methacrylate) comb polymers
Methacrylate comb polymers were synthesized that have amphiphilic teeth of ethylene glycol oligomers capped with alkyl groups. Both segments are of exact length to promote self-organization and crystallization. The atactic methacrylate backbone plus close proximity to the polymer backbone inhibits crystallization of the oligoethyelene oxide segments, but the terminal alkyl segments readily crystallize. Wide-angle X-ray diffraction and differential scanning calorimetry were used to characterize polymer side chain crystallization and its evolution as a function of the length of the amphiphilic teeth. An analysis of the d spacings places the oligoethylene glycol segment and the first eight carbon atoms of the alkyl chain in an amorphous phase. An similar to 1 angstrom/carbon atom increase in the d spacing is consistent with the crystalline segments being tilted relative to the polymer backbone. When the number of carbon atoms in alkyl segments is >= 14, addition of LiClO4 yields an ionic conducting ethylene oxide phase with retention of the alkyl crystallization. These novel polymer electrolytes use crystallization as a structural element to maintain dimensional stability.