Recovery Stress and Work Output in Hyperbranched Poly(ethyleneimine)-Modified Shape-Memory Epoxy Polymers

In this study a series of hyperbranched modified shape-memory polymers were subjected to constrained shape recoveries in order to determine their potential use as thermomechanical actuators. Materials were synthesized from a diglycidyl ether of bisphenol A as base epoxy and a polyetheramine and a commercial hyperbranched poly(ethyleneimine) as crosslinker agents. Hyperbranched polymers within the structure of the shape-memory epoxy polymers led to a more heterogeneous network that can substantially modify mechanical properties. Thermomechanical and mechanical properties were analyzed and discussed in terms of the content of hyperbranched polymer. Shape-memory effect was analyzed under fully and partially constrained conditions. When shape recovery was carried out with fixed strain a recovery stress was obtained whereas when it was carried out with a constraining stress the material performs mechanical work. Tensile tests at Tg(E)' showed excellent values of stress and strain at break (up to 15 MPa and almost 60%, respectively). Constrained recovery performances revealed rapid recovery stress generation and unusually high recovery stresses (up to 7 MPa) and extremely high work densities (up to 750 kJ/m(3)). The network structure of shape-memory polymers was found to be a key factor for actuator-like applications. Results confirm that hyperbranched modified-epoxy shape memory polymers are good candidates for actuator-like shape-memory applications. (C) 2016 Wiley Periodicals, Inc.