Synthesis of Novel (Meth)acrylates with Variable Hydrogen Bond Interaction and Their Application in a Clear...

Clear viscoelastic films (CVFs) have many applications in the display industry. Acrylic monomers containing a hydrogen bond (H-monomer) are often used in the preparation of CVF to increase the cohesion and form favorable interactions with the display substrate. Common H-monomers face a counterbalance between the glass transition temperature (T_g) and the hydrogen-bonding association constant (K_a). Strong hydrogen bonding often leads to a high T_g and high modulus, which are unfavorable in certain applications such as foldable display. To solve these problems, four types of hydrogen-bonding (meth)acrylic monomers (carbamate acrylate, carbamate methacrylate, urea acrylate, and urea methacrylate) with different K_a and T_g were readily synthesized. Among them, urea acrylates displayed the highest K_a while still maintaining moderate T_g. These H-monomers were copolymerized with 2-ethylhexyl acrylate (EHA) and cross-linked to obtain a series of copolymers (H-copolymers) as pressure-sensitive adhesives. After the characterization of rheology, optics, and peel adhesion, urea-acrylic H-copolymers showed the best overall performance by combining great optical property (>98% in transmittance, < 1% in haze) and mechanical performance (8-12 N/25 mm in peel adhesion, 84-92% in creep recovery). This work provides a new path to prepare acrylic CVF for flexible display application.