Synthesis of urethane-modified aliphatic epoxy using a greenhouse gas for epoxy composites with tunable properties: Toughened polymer, elastomer, and pressure-sensitive adhesive

Epoxy, which exhibits tunable mechanical properties, has been investigated to overcome its inherent brittleness and extend its application range. Herein, various epoxy composites, including a toughened polymer, elastomer, and pressure-sensitive adhesive (PSA), with tunable mechanical properties were prepared by adjusting the ratio of a rigid aromatic epoxy and flexible aliphatic epoxy. A flexible aliphatic epoxy that incorporated urethane linkages was used to extend the tuning range; it was synthesized via an eco-friendly route utilizing CO2 without isocyanate. The prepared toughened polymer-like and elastomeric epoxy composites can be used in structural epoxy adhesive (lap shear strength = 27.8 MPa) and flexible electronics (plastic strain < 10%), as confirmed through single lap shear, cyclic tensile, and Izod impact tests, respectively. The most flexible among the prepared epoxy composites exhibited PSA properties (peel strength = 6.8 N·cm−1) that were comparable to those of conventional tapes. A viscoelastic window also supported that the prepared PSA can be utilized as a general-purpose PSA and a removable PSA. This work proposes a new application of eco-friendly epoxies and a strategy to facilitate the wide tuning range of epoxy materials, including PSAs.