Many biological systems make use of chemical fuels such as ATP. Inspired by this, recent work focuses on using chemical fuel reactions in non-biological systems. This project focuses on the hydration of carbodiimides as the fuel reaction. Carbodiimide hydration can be used to link carboxylic acids as anhydrides. Using EDC fueled anhydride formation, dynamic crosslinks can be formed in polymers with -COOH pendant groups . Temporary changes in mechanical properties result from a transient network of anhydride crosslinks which eventually dissipate by hydrolysis. This research focuses on transient polymer networks where the effect of permanent and transient crosslink density of the polymer is analyzed. Network strength was evaluated using rheological time sweep experiments. The peak storage moduli were measured to determine transient crosslinking density. Permanently crosslinked single network polymers were prepared by RAFT polymerization using acrylic acid and acrylamide as monomers and <i>N,N-M</i>ethylenebisacrylamide as crosslinker. In the presence of EDC, the pendent carboxylic acid groups form anhydride bonds increasing network strength. Over the time, the anhydride bonds hydrolyze back to the initial carboxylic acid groups. The time-dependent mechanical properties could be modulated by the concentration of carbodiimide, temperature, and primary chain architecture. Because the materials remain rheological solids, applications such as temporally controlled adhesives and rewritable spatial patterns of mechanical properties are possible.

Chemically fueled reinforcement of polymer hydrogels

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ACS Spring 2023

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