Green, Removable Adhesive Based on Graft Copolymers of Aliphatic Polyesters for Multiple Types of Substrates

Adhesive is a widely used material. However, most of traditional synthetic adhesives are difficult to be peeled and removed without damaging the adherends due to their excellent chemical stability and strong interaction (covalent bonds, physical interactions, or their combinations) with the substrate surfaces. Therefore, complete and efficient recovery of the substrates has become a huge challenge. In this work, a green, removable adhesive based on graft copolymers of aliphatic polyesters, i.e., PPDO (poly(1,4-dioxan-2-one)) and PCL (poly(epsilon-caprolactone)) was prepared through one-pot ring-opening polymerization using polyvinyl alcohol (PVA) as the macro-initiator. The graft copolymers have abundant graft chains and hydroxyl end groups owing to their comb-like molecular topology, which therefore act as active sites for bonding with the substrate surfaces. The graft copolymers showed considerable adhesive strength to various substrates, including stainless steel plates (lap shear strength >1 MPa), woods (>1 MPa), glasses with a very low surface roughness (<10 nm) (0.62 ± 0.04 MPa), and plastics with low surface energy such as PE (T-peel strength: 427.0 gf/25 mm). Furthermore, the adhesives based on aliphatic polyesters could be easily debonded under a relatively mild condition through degradation when they were taken out of service, thus realizing the intact recovery of the substrates. The debonded adhesive and its degradation products could be further depolymerized to monomers with a very high purity (>99.5%) by acidification–dehydrative cyclization or simple pyrolysis (150 °C) under vacuum. In the whole life cycle, almost no versatile organic compounds were used. In addition, CCK8 experiments proved that the graft copolymer adhesive had no toxicity to HEK 293T human cells, indicating that it is a green adhesive with great potential.