Poly(n-hexyl methacrylate) Covalent Adaptable Networks (CANs) Made by Reactive Processing to Link Alkyl Side Chains with Dynamic Covalent Bonds

Covalent adaptable networks (CANs) may be synthesized by a variety of methods, with the most common being synthesis from monomers. Reactive melt-state processing provides a simple procedure for grafting dynamic crosslinkers onto precursor linear or branched polymers, also resulting in CANs. Reactive processing also allows for the direct examination of structure-property relationships between the precursor polymers and CANs. Here, we synthesized poly(n-hexyl methacrylate) (PHMA) samples of various molecular weights and prepared CANs via reactive processing to graft dialkylamino disulfide dynamic crosslinkers between PHMA side chains. We characterized how crosslinker loading and precursor molecular weight affected the rubbery plateau modulus (which is directly proportional to crosslink density according to Flory’s ideal rubber elasticity theory), stress relaxation time, and elevated-temperature creep resistance of the CANs. By comparing to a previous published study of PHMA CANs made by copolymerization of hexyl methacrylate with dialkylamino disulfide crosslinkers (with the crosslinkers attached to the chain backbone), we determined that the activation energies of stress relaxation and creep viscosity are the same within experimental uncertainty but a function of how the crosslinker is attached to the PHMA chains; the time and temperature conditions for reprocessing were also a function of the method of CAN synthesis. These outcomes demonstrate the importance of synthesis-structure-property-reprocessing relationships in CANs.