Influence of hydrogen bonding interactions, entanglement, and covalent crosslinking on the viscoelasticity of acrylic viscoelastomers containing urea group

The structure-property relationship of acrylic clear viscoelastomer films (acrylic CVFs) as foldable optical clear adhesives (OCAs) has always been unclear. In our work, a series of acrylic CVFs with different hydrogen-bonding interactions (H-bondings) and cross-linking densities (namely, CL-H-copolymers) were synthesized. The effects of entanglement, H-bonding, and covalent crosslinking on the recovery and adhesive properties of CL-H copolymers were analyzed by rheology, equilibrium swelling, and tensile stress-strain tests (tensile tests). The structural parameter M-x/M-e(H) was obtained by combining the affine deformation model, the Flory-Rehner equation, and the UCM-Gent model, where Mx is the molecular weight between covalent crosslinkers and M-e(H) is the a physical crosslinking molecular weight affected by H-bondings. The experimental results showed that the CL-Hcopolymers had an obvious dependence on Mx/MeH. Recovery properties tended to stabilize (>90 %) at M-x/ M-e(H) < 1, while adhesion strengths continued to decrease with decreasing M-x/M-e(H). This conclusion and methodology are instructive for the design of foldable OCAs with high elasticity and high adhesion performance.