Acrylic pressure-sensitive adhesives based on ethylene glycol acrylate for flexible display application: Highly elastic and recoverable properties

New acrylic PSAs with a high flexibility were synthesized using 2-(2-ethoxyethoxy)ethyl acrylate (EEA), an ethylene glycol-based acrylate. Compared to acrylic PSAs based on 2-ethylhexyl acrylate (EHA) and octyl acrylate (OA), acrylic PSA based on EEA was found to form physical crosslinking due to improved chain entanglement and increased secondary bonding by the ethylene glycol and hydroxyl groups. These properties showed behaviors similar to those caused by crosslinking, which improved the elasticity of acrylic PSA and resulted in a fast recovery rate and high recovery characteristics of more than 70%. In addition, it was confirmed that the physical crosslinking supplemented the cohesive strength of the acrylic PSA, which showed relatively excellent adhesion properties compared to EHA and OA despite a low modulus of less than 106 Pa. The properties of EEA-based acrylic PSA were controlled by the photoinitiator (PI) and chain transfer agent (CTA), and the effect of reaction conditions on EEA-based acrylic PSA was analyzed based on this. The PI did not affect the molecular weight of the acrylic PSA, and only the reaction rate was controlled by the radical content. On the other hand, the CTA showed sufficient control over the molecular weight and molecular weight distribution of acrylic PSAs. The viscoelastic properties of the acrylic PSA also showed no significant change in response condition control, indicating excellent elasticity, regardless of the conditions. The PI influenced the creep and recovery characteristics of the acrylic PSA through plasticization, and excellent stress relaxation characteristics were confirmed by the controlled glass transition temperature.