High‐Strain Shape‐Memory Polymers

Abstract Shape‐memory polymers (SMPs) are self‐adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures. In this study, the glass transition temperature ( T g ) is adjusted between 28 and 55 °C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA). Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a T g of 28 °C, at 663% for a T g of 37 °C, and at 553% for a T g of 55 °C. A new compound, 4,4′‐di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape‐memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%. The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape‐memory cycle caused large‐scale disfiguration. The materials in this study are intended to enable future applications where both recoverable high‐strain capacity and the ability to accurately and independently position T g are required.