Microplastics are pervasive aquatic contaminants, yet conventional size-exclusion membrane filters exhibit limited capture efficiency. Moreover, existing surface-modification rely on permanent hydrophilic or hydrophobic coatings, limited reusability, and poor stability. A key challenge is achieving eco-friendly, aqueous-processable coatings stable under continuous water exposure. To address these challenges, we propose a polarity-switchable copolymer containing maleic anhydride (MA). Base-induced ring opening converts the copolymer into a hydrophilic, water/ethanol-soluble, while subsequent thermal treatment restores its hydrophobic state through ring closing. This polarity switching enables the formation of an eco-friendly adhesive coating on filtration membranes, enhancing microplastic capture efficiency. This adhesive layer mitigates pressure-drop and suppresses fouling during prolonged operation, while polarity switching enables membrane reuse without toxic organic solvents.