Mixed “Nonsolvents” Induced Phase Separation of Amphiphilic Long-Chain Polyurethanes

In this study, phase separation of long-chain polyurethanes (LCPUs) induced by evaporation of mixed “nonsolvents” was investigated. The amphiphilic nature of LCPUs, consisting of alternating high-polar segments (urethane groups) and low-polar segments (alkyl chains), allows their dissolution in a mixture of high-polarity solvent and low-polarity solvent; both of which are nonsolvents of LCPUs when used individually. The sequential evaporation of two nonsolvents triggers phase separation of LCPU solutions, namely, “mixed 'nonsolvents' evaporation induced phase separation” (MNEIPS). The dependence of pore sizes and porosities of LCPU membranes on the length of alkyl chains, the initial polymer concentration, and the solvent compositions was investigated in detail. In addition, we demonstrated the application of LCPU membranes as separators in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). This work expands the scope of amphiphilic polymers and provides unique insights into the development of functional long-chain polycondensates.