Abstract
Tough adhesives provide resistance against high debonding forces, and these adhesives are difficult to design because of the simultaneous requirement of strength and ductility. Here, we report a design of tough reversible/recyclable adhesive materials enabled by incorporating dynamic covalent bonds of boronic ester into commodity triblock thermoplastic elastomers that reversibly bind with various fillers and substrates. The spectroscopic measurements and density functional theory calculations unveil versatile dynamic covalent binding of boronic ester with various hydroxy-terminated surfaces such as silica nanoparticles, aluminum, steel, and glass. The designed multiphase material exhibits exceptionally high adhesion strength and work of debonding with a rebonding capability, as well as outstanding mechanical, thermal, and chemical resistance properties. Bonding and debonding at the interfaces dictate hybrid material properties, and this revelation of tailored dynamic interactions with multiple interfaces will open up a new design of adhesives and hybrid materials.
Highlights
Adhesives have been used in all aspects of our daily life to connect materials temporarily or permanently [1]
SEBS triblock copolymer (118 kg/mol) with 30 mole percent styrene was modified via aromatic C-H borylation to incorporate dynamic boronic ester functional groups to yield a borylated SEBS triblock copolymer (S-Bpin) (Fig. 2A) [47]
The aromatic C-H protons of styrene in the 1H nuclear magnetic resonance (NMR) spectrum split into three broad peaks at the 6.0- to 7.8-ppm region, indicating successful functionalization on the aromatics, while pinacol boronate ester (Bpin) methyl protons were overlapped with the SEBS backbone methylene peak
Summary
Adhesives have been used in all aspects of our daily life to connect materials temporarily or permanently [1]. Synthetic polymers have been widely used as adhesive materials due to their capability to provide good contact between surfaces and dissipate energy under stress [2,3,4]. Load-bearing adhesives for structural applications including epoxies, polyurethanes, or acrylics typically provide strong adhesion, but their low work of debonding due to brittleness often leads to undesired cohesive failure (red curve in Fig. 1) [5]. Ductile adhesives are made of low modulus materials that limit their use in structural applications. Tough adhesives are characterized as having high degrees of debonding force (green curve in Fig. 1), which will provide improved safety and longevity of the structure with minimizing adhesive failures, and successful development of remarkably tough adhesives will affect many applications in the electronic, construction, and automotive industries [5]
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