Ultra-high molecular weight tanglemer hydrogels

Abstract

Developing hydrogels that combine excellent mechanical strength with biocompatibility remains a challenge, particularly for designing materials for biomedical applications. We report the synthesis of ultra-high molecular weight poly(2-hydroxyethyl acrylate) hydrogels via xanthate-mediated photoiniferter reversible-deactivation radical polymerization. We systematically investigated the effects of changing the targeted degree of polymerization (500 to 50,000), crosslinker amount (0.001 - 2 mol%), and monomer concentration (0.5 - 5 M) on the mechanical properties and swelling behavior of the hydrogels. For our system, we found that the transition between crosslink-dominated gelation to entanglement-dominated gelation occurred at a degree of polymerization exceeding 5,000. The hydrogel prepared from a 5 M reaction mixture with 0.005 mol% crosslinker gave optimal mechanical properties, with a compressive strength approaching 1 MPa and toughness of 168.6 kJ/m3. These findings establish that minimal chemical crosslinking combined with dense polymer entanglements provides superior mechanical properties compared to conventional crosslinking strategies, offering design principles for next-generation tough hydrogels.