Study on UV-Curable Acrylic Clear Viscoelastic Materials with Grafted Structures

Flexible substrates are crucial for wearable electronic strain sensors, but achieving biocompatibility, low cost, and aesthetic appeal alongside good mechanical performance remains challenging. Acrylic-based clear viscoelastic films (CVFs) are gaining attention due to their excellent transparency and potential for enhanced mechanical properties. This study synthesized copolymers CVF1-4 with varying branch content using soft monomers 2-ethylhexyl acrylate (2-EHA), butyl acrylate (n-BA), and functional monomer acrylic acid (AA). Employing a "grafting-through" strategy, small molecule monomers, ATRP-synthesized oligomer pBA25, and photoinitiator 1,6-hexanediol diacrylate (HDDA) were in-situ polymerized under UV light to form transparent, flexible elastic films CVF1-4. Between -20 to 80 C, CVF1-4 demonstrated excellent mechanical properties such as low modulus (in the kPa range), low glass transition temperature (below -20 C), large deformation (500-600%), and high strain recovery rate (>95%). Among them, CVF3 with 15% branching showed a balanced comprehensive performance, exhibiting primarily elastic behavior at room temperature. Therefore, selecting appropriate molecular composition and grafting structure provides a simple and customizable solution for optimizing CVF properties.