Encapsulation of polymer chains into nanochannels of metal-organic frameworks (MOFs) to construct polymer-MOF hybrid materials can retain the desired properties of two disparate materials. However, the facile fabrication of such hybrids remains challenging, given the difficulty in unraveling entanglement of polymer chains and constraining them into ordered conformations. Herein, we introduce an in situ molecular weaving strategy to construct ionic polymer-MOF hybrid materials, employing shear forces and coordination interactions to untangle cationic polymer chains and guide their realignment within MOF nanochannels during framework formation. Notably, this realignment promotes uniform polymer distribution and exposes more anion-exchange sites. The resulting hybrids capture ReO₄^¯ (a nonradioactive surrogate of ⁹⁹TcO₄^¯) with a capacity of 438 mg g^-1 and reach adsorption equilibrium within 20 min. Characterization and theoretical calculations reveal that the hydrophobic pores in the hybrid materials confer strong affinity toward less hydrated ⁹⁹TcO₄^¯ anions, thereby enhancing their selectivity over competing anions.