Covalent adaptable networks (CANs) are smart, crosslinked polymers, based on dynamic covalent chemistry that enables bond rearrangement within the networks in response to the application of a specific applied stimulus. This behavior gives CANs the ability to act as a bridge between thermosets and thermoplastics, given that they can be remolded after polymerization while maintaining many useful proprieties associated with thermosets such as the mechanical strength and solvent resistance. Taking a lesson from controlled radical polymerization approaches that incorporate reversible termination or transfer reactions, specifically, CANs with bonds that participate in reversible addition-fragmentation chain transfer (RAFT), exhibit radically triggered adaptability. This behavior leads to several distinct advantageous material characteristics. For example, incorporation of the RAFT functionalities into the backbone of the polymer networks permits spatio-temporal control of the network rearrangement in response to an applied stress during light irradiation.<br/>Herein, we demonstrate the ability of RAFT to relax stress in glassy networks formed by copper(I)-catalyzed azide-alkyne (CuAAC) polymerizations by designing different monomers containing allyl sulfide moieties. CuAAC, as a highly efficient and orthogonal click reaction, produces rigid triazoles as a product which enhances mechanical performance and forms glassy networks. The influence of RAFT rearrangement on the mechanical performance and shrinkage induced stress was examined. Additionally, nano/micro topographical patterns were created in CuAAC networks by post-polymerization stress relaxation in the glassy state. Furthermore, we demonstrated a fundamentally new approach to improve composite behavior via localized stress relaxation in glassy composites.

Using addition-fragmentation chain transfer in polymer networks to achieve stress relaxation and improve material performance

254th National Meeting (2017)

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