Structure–Property Mechanisms in Low-Modulus RAFT-Mediated Triblock Supramolecular Hydrogels: Network Entanglement and Crystalline Domain Control

Abstract

Hydrogel reinforcement strategies commonly rely on compositional or network-structure regulation, whereas the structure–property relationships of block copolymer hydrogels prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization remain insufficiently understood. Here, we construct bottlebrush-like, inter-crosslinked triblock copolymer hydrogels with tunable block molecular weights using UPy derivatives (UPyMA/UPyHMA) based on quadruple hydrogen-bonding motifs. Two structurally controlled hydrogels, P(AM-b-UPyMA-b-AM) (PUA) and P(AM-b-UPyHMA-b-AM) (PHA), were synthesized. PUA undergoes polymerization-induced self-assembly (PISA), driven by phase separation induced by the Flory–Huggins χ parameter, to form densely packed nanorod structures. Combining tube-model analysis with structural characterization, we establish the relationships among crosslinking-segment molecular weight, apparent entanglement molecular weight (Me), and mechanical properties. Moderate increases in crosslinking-segment molecular weight synergistically enhance network stiffness and entanglement density. The ordered crystalline domains formed by UPy hydrogen bonding, π–π stacking, and hydrophobic interactions enable PUA to reach a fracture strength of 0.13 MPa—comparable to conventional free-radical hydrogels—while its Young’s modulus (0.020 MPa) is only half. The PUA triblock copolymer hydrogel also exhibits a high swelling ratio (2900% in PBS) and slow degradation over 264 h, combining high water absorbency with superior network stability and showing promise for biomedical applications.