Elucidating microphase separation in perfluoropolyether triblock copolymers using scattering techniques

Short chain perfluoropolyether (PFPE) polymers have recently been shown to conduct and solvate lithium salts, and thus can be used as homopolymer electrolytes for battery applications. In an attempt to improve the transport characteristics, poly(ethylene oxide) (PEO) has been covalently bonded to the ends of PFPEs to form triblock copolymers of type A-B-A. By increasing the lengths of the PEO segments, the segregation strength of the copolymers increases; at the highest PEO molecular weight, the copolymers microphase separate. While phase separation was not immediately apparent using small angle X-ray scattering (SAXS), measuring birefringence with depolarized light scattering (DPLS) allows for the conclusion of phase separation. The Flory-Huggins interaction parameter between PEO and PFPE was calculated to determine the segregation strength as a function of salt concentration. This work provides thermodynamic data on the interactions between non-fluorinated end-groups and fluorinated backbones.