Conformational, Mechanical, and Ring-Sliding Properties of c2Daisy Chain Network Thin Films under Biaxial Deformation

Y Wang and GQ Liu and ZM Zhang and XZ Yan, MACROMOLECULES, 58, 12606-12618 (2025).

DOI: 10.1021/acs.macromol.5c02032

Mechanically interlocked polymers (MIPs) offer distinctive topologies that enable materials with enhanced mechanical and dynamic properties. Here, we combine c2daisy chains with three-arm cross-linkers to build mechanically interlocked network (MIN) bulk systems and free-standing thin films. By systematically varying the extension distance n, cross- linking degree c, and strain rate epsilon, we probe conformational, dynamical, mechanical, ring sliding, and bond scission properties. In bulk, MINs with larger n lower the glass transition temperature, consistent with experimental observations. Locally, rings exhibit the highest local molecular stiffness, followed by binding sites and axle chains. In thin films, smaller n yields slightly more extended chain conformations, as revealed by radius of gyration, end-to-end distance, and shape descriptors. Increasing c produces more complete networks, strengthens topological constraints, and reduces chain mobility. Under biaxial stretching, MIN thin films with smaller n, larger c, and higher epsilon display higher yield stress, higher flow stress, and greater toughness. Morphology analysis indicates that a critical cross-linking level of c >= 0.75 is required for network percolation at large strain. In addition, we declare that a lower epsilon facilitates substantial ring sliding. Using a bonded ring reference, we find that ring sliding suppresses excessive bond scission, preserves network integrity at large strains, and delays failure, thereby improving toughness. Finally, employing a Morse bond potential enables substantial bond scission during loading and reproduces the experimental trend that longer n postpones failure and increases toughness. These results clarify the deformation mechanisms in MINs and guide the design of mechanically robust materials.

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