AB-type monomer design for cleavable polyurethanes: conjugate substitution-induced main-chain scission for removable adhesives

Polyurethanes that degrade via main-chain scission under ambient conditions were designed. Monomer precursors were synthesized via the Morita-Baylis-Hillman reaction of acrylates with terephthalaldehydic acid, followed by azidation. Subsequent Curtius rearrangement afforded AB-type monomers containing both isocyanate and hydroxy groups, and their self-polyaddition yielded a series of polyurethanes exhibiting solubility and glass transition temperatures depending on the structures of the pendant alkyl groups. Because the allylic positions of the methacrylate moieties were substituted with carbamate groups, treatment with diethylamine efficiently induced quantitative conjugate substitution under ambient conditions, resulting in main-chain scission accompanied by decarboxylation. Importantly, copolymers containing another AB-type monomer lacking methacrylate moieties underwent degradation via a self-immolative pathway triggered by conjugate substitution. The resulting polyurethanes functioned as adhesives for glass plates with a lap shear strength of 0.28 MPa and were readily removed by treatment with methanolic diethylamine solution.