Building tunable degradation into high-performance poly(acrylate) pressure-sensitive adhesives

Pressure-sensitive adhesives (PSAs) based on poly(acrylate) chemistry are
common in a wide variety of applications, but the absence of backbone
degradability causes issues with recycling and sustainability. Here, we
report a strategy to create degradable poly(acrylate) PSAs using simple,
scalable, and functional 1,2-dithiolanes as drop-in replacements for
traditional acrylate comonomers. Our key building block is α-lipoic acid,
a natural, biocompatible, and commercially available antioxidant found in
various consumer supplements. α-Lipoic acid and its derivative ethyl
lipoate efficiently copolymerize with n-butyl acrylate under conventional
free-radical conditions leading to high–molecular-weight copolymers (Mn
> 100 kg mol–1) containing a tunable
concentration of degradable disulfide bonds along the backbone. The
thermal and viscoelastic properties of these materials are practically
indistinguishable from non-degradable poly(acrylate) analogues, but a
significant reduction in molecular weight is realized upon exposure to
reducing agents such as tris(2-carboxyethyl)phosphine (e.g. Mn = 198 kg
mol–1 → 2.6 kg mol–1). By virtue of the thiol chain ends
produced after disulfide cleavage, degraded oligomers can be further
cycled between high and low molecular weights through oxidative
repolymerization and reductive degradation. Transforming otherwise
persistent poly(acrylates) into recyclable materials using simple and
versatile chemistry could play a pivotal role in improving the
sustainability of contemporary adhesives.