Ductile Glassy Polymer Networks Capable of Large Plastic Deformation and Elastic Recovery

Abstract

Many thermoplastic polymers exhibit outstanding ductility by combining strength and large deformations. These large deformations are irreversible — known as plastic deformation. Elastomers are capable of large, reversible deformation — known as elastic deformation — but have low strength. To this end, we developed glassy and ductile polyamide networks capable of large plastic deformation (>200% strain) and high strength (~50 MPa tensile strength and ~1500 MPa Young’s modulus), similar to the tensile properties of polyolefins and Nylon 66. We discovered that hydrogen bonding between meta-phthalamide groups was essential to the ductility. Since these polyamide networks are covalently bonded, we demonstrated their unique durability enabled by repeatable elastic recovery at elevated temperatures, exhibiting indifferent tensile properties in each cycle. Furthermore, when we fixed the strain during the elastic recovery, these polyamide networks actuated stresses of 9-18 MPa, among the highest found in shape-memory polymer actuators. We envision these ductile, glassy polymer networks as promising alternatives to many thermoplastic polymers, given the combined benefit of ductility and durability.