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German Parada1 Xuanhe Zhao1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Ideal Reversible Polymer Networks have well-controlled network structures similar to ideal covalent networks but exhibit transient properties due to the presence of reversible crosslinks. We have developed a theory to describe the mechanical properties of these ideal reversible polymer networks under small shear deformation, and have predicted that the networks behave as a single Maxwell element of a spring and a dashpot in series, with the instantaneous shear modulus and relaxation time determined by the concentration of elastically-active chains and the dynamics of reversible crosslinks, respectively. Due to the use of short polymer chains, we expected no contributions from polymer chain entanglements or chain relaxation, as the Rouse relaxation time is much shorter than the reversible crosslinks’ characteristic time. The theory also provided general methods to (i) independently control the instantaneous shear modulus and relaxation time of the networks, and to (ii) quantitatively measure kinetic parameters of the reversible crosslinks, including reaction rates and activation energies, from macroscopic viscoelastic measurements. The theory and methods were validated experimentally using a 4-Arm polyethylene glycol hydrogel system. We have also employed the theoretical and experimental system developed to characterize the fracture modalities and mechanical properties under large uniaxial deformation at varying loading rates.

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