Interpenetrating networks (IPN) contain two or more networks which not covalently bonded each other, but they cannot be isolated unless bonds are broken. Single Networks (SN) contains only one type of networks and covalently crosslinked. IPNs can enhance properties and introduce new properties to the material. More entanglements in IPN create ‘entanglement force’ or ‘cohesive force’ which can act as intermolecular locking forces within the networks as in the tube model. This cause higher stress at break in IPN compare to SN. In addition to the polymer architecture, incorporation of thermoresponsive dynamic covalent linkages into these polymer networks can further enhance the thermo-mechanical properties of a material. In this study used Thiol-Michael bonds as the crosslinker which is active above 90 °C. Dynamic nature of the Thiol-Michael crosslinker allows the transition of IPNs into SN above 90 °C resulting similar polymer architecture in both SN and IPN. Once the IPN heated up to 90 °C, Thiol-Michael bonds can activate and exchange with each other resulting a single network type polymer. This results similar self-healing stress-strain curves for both SN and IPN. Furthermore, diluted polymerization solution can lead to have more loops within the single networks resulting negative impact on mechanical properties. Those defects are higher in SN compare to IPN. However, heating helps to reduce the number of floppy loops created in the networks by concentrating the polymer material. In addition to concentrating, dynamic nature of the TM crosslinker helps to unfold those loops at higher temperature and strengthen the network. In this study, we have synthesized SN and IPN using Hydroxy Ethyl Acrylate as the monomer and TMMDA (Thiol-Michael Adduct) as the thermoresponsive dynamic crosslinker. Materials were characterized thermally and mechanically including self-healing ability, tensile strength, Dynamic mechanical Analysis and Differential Scanning Calorimetry.

Dynamic covalent chemistry for architecture changing interpenetrated and single networks

ACS Fall 2021

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