Bottlebrush elastomers as pressure sensitive adhesives*

PSA materials possess unique rheological properties, exhibiting bonding-debonding dualism. During slow bonding, they display a low modulus that facilitates penetration of substrate roughness, whereas at faster debonding, the same material demonstrates a higher modulus, which is vital for generating high tack and preventing cohesive rupture at large deformations. To optimize the bonding-debonding interplay, PSAs are made by mixing polymer networks with large quantities of plasticizers and tackifiers that are prone to migration, resulting in ill-defined property variation over time and surface contamination. We have outlined a general framework for the design of additive-free adhesives, where properties are controlled by polymer brush architecture. Bottlebrushes suppress chain entanglements, enabling preparation of super-soft elastomers with a modulus as low as 100 Pa, which satisfies the Dahlquist criterion for spontaneous substrate wetting. Furthermore, by varying architectural parameters, we demonstrated unprecedented control over the work of adhesion spanning almost 5 orders of magnitude without changing chemical composition or using additives. This design platform was extended to the design of hot-melt pressure sensitive adhesives (HMPSAs), based on self-assembly of bottlebrush graft-copolymers, where side chains behave as softness, strength, and viscoelasticity mediators. These systems maintain moldability of conventional thermoplastic elastomers, while the brush architecture provides elastic softness at small deformations, intense strain-stiffening at large deformations, low melt viscosity, and a wide-ranged control of viscoelastic response.