Synthesis and characterization of ultra-high molecular weight hydrogels via photo-initiated aqueous RAFT polymerization Gavin Irvine , Maciek Kopec University of Bath, UK Conventional radical polymerization techniques yield high molecular weight polymers but afford no synthetic control over the polymerization. On the other hand, controlled polymerization techniques afford excellent control but have proved difficult in forming ultra-high molecular weight (UHMW) polymers. Recently, however, synthesis of UHMW linear polymers using photo-initiated controlled radical polymerization techniques has been studied in literature [1]. We set out to synthesize UHMW poly(N,N-dimethylacrylamide) (PDMA) hydrogels and analyze their physical properties. Herein, I describe the formation of UHMW PDMA gels using UV-initiated aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The gels were synthesized with targeted degrees of polymerization (DP) between 100 – 100,000 ( M n 990 – 9.9 x 10 6 g/mol) with N,N’-methylenebisacrylamide (MBAm) crosslinker. Equilibrium swelling ratio (ESR), shear storage modulus ( G’ ), compression stress and kinetic data were obtained for each targeted DP, while keeping a constant crosslinker loading (10 mol% of MBAm). Interestingly, both G’ and ESR tend to plateau at high targeted DP (above 10,000) despite drastically decreased crosslinking density, indicating the formation of highly entangled hydrogels. These entanglements act as transient crosslinks and are responsible for the hydrogel’s softness and elasticity, while sparse covalent crosslinks help to maintain its structural integrity [2]. References 1. R. Nicholas Carmean, T. E. Becker, M. B. Sims, B. S. Sumerlin, Chem, 2017, 2 , (1), 93-101. 2. J. Kim, K. G. Zhang, M. Shi, Z. Suo, Science, 2021, 374 , 212-216.
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