Cation-π Dynamic Cross-Linking Enabled High-Performance PVA Films With Synchronous Strength-Toughness Enhancement, Self-Healing, and Recyclability.

Poly (vinyl alcohol) (PVA), a representative biodegradable and water-soluble polymer, suffers from high crystallinity, a strength‑toughness trade‑off, and poor thermal stability arising from strong interchain hydrogen bonding. Conventional modification strategies fail to simultaneously achieve synergistic enhancement of strength-toughness and functionalization, severely restricting its engineering applications. Herein, inspired by the robust yet dynamic nature of cation-π interactions, we present a universal design strategy for high-performance water-soluble polymers based on indole-Mg2+ cation-π dynamic cross-linking. Molecular simulations and spectroscopic characterization demonstrate that Mg2+ forms strong cation-π interactions with indole moieties, exhibiting a binding energy of -113 kJ mol-1. Mechanical testing reveals that the optimally formulated PVAI-7.5%Mg2+ film achieves a tensile strength of 51 MPa (a 130% increase from 22 MPa) and an elongation at break of 400% (enhanced from 320%), thereby realizing synchronous improvement of strength and toughness. Benefiting from the dynamic reversibility of cation-π interactions, the film exhibits autonomous scratch healing within 12 h at room temperature without external stimuli, while retaining excellent water solubility that enables multiple recovery and reprocessing cycles via solvent-based methods without performance degradation. This study overcomes the dual bottlenecks of the strength-toughness trade-off and the performance-functionalization incompatibility inherent to PVA modification, offering new avenues for the high-performance and multifunctional design of water-soluble polymers and providing experimental and theoretical insights into the application of cation-π interactions in polymeric materials.