Microphase separation of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) block copolymers induced by differential interactions with salt

This work describes the microphase separation behavior of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs), a type of new sulfur-containing block copolymer, induced by lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI). PPMTC-b-PEO BCPs with a fixed PEO block length but different PPMTC block lengths were synthesized and doped by LiTFSI. Temperature-variable small-angle X-ray scattering result indicates that microphase separation of the PPMTC-b-PEO BCPs can be induced by differential interactions with LiTFSI. However, the ability of LiTFSI to induce microphase separation in PPMTC-b-PEO BCPs does not monotonically increase with the doping ratio (r = [Li⁺]/([EO] + [PMTC])). It is observed that stronger microphase separation usually occurs at r = 1/12 and 1/6, but microphase separation is weaker at r = 1/24 and 1/3. In most cases, microphase-separated but disordered structures are obtained. Particularly, ordered lamellar structure is formed at suitable doping ratio and block composition. FTIR result confirms the differential complexation of LiTFSI with PEO and PPMTC. LiTFSI preferentially interacts with PEO at low rs, but also strongly interacts with PPMTC at high rs. This work provides a new method to prepare solid polymer electrolytes with double conductive nano-phases, which may be beneficial to both conducting and mechanical properties.