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 M_x 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-H-copolymers had an obvious dependence on M_x/M_e^H. 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.