Amorphous polymers separate small organic molecules with switchable selective states

Structured porous materials, including metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), are being intensely developed because they can separate small molecules via precisely constructed and uniformly sized pores, despite challenges that hinder practical use. Polymers are structurally amorphous; hence, they are not considered fundamentally capable of separating different organic molecules. This manuscript reports that amorphous polymers can be prepared to separate different small organic molecules (i.e., solutes dissolved in a solvent) effectively, with very large separation factors of ~1000 and ~100,000. Effective separation involves fundamentally a delicate balance between hydrophobicity and hydrophilicity and dynamic mobility of polymeric chains to produce optimal pores. Therefore, structured pores are not fundamentally essential for molecular separation — amorphous pores are effective. These stimuli-responsive polymers have reversibly switchable states with completely opposite selectivities. They are multifunctional: they separate by polarity, size, and with opposite selectivities. Hence, they can separate many different molecules in complex solutions. These polymers are simple and inexpensive to fabricate for widespread use.