Solid state reaction of bifunctional bicyclo orthoesters and carboxylic acids and their metal adhesive properties

Five kinds of novel bifunctional bicyclo orthoesters (BOEs) were synthesized and copolymerized with multi-functional carboxylic acids, having plural carboxyl and hydroxyl groups, to develop functional materials usable as non-volatile adhesives. In a solid-state reaction of BOEs with the carboxylic acids, mechanical mixing converted the BOE moiety to a corresponding hydrolyzed form via ring-opening and isomerization reactions. The solid-state reaction, requiring moisture and mechanical stress, was accelerated by the higher reactivity given by the α-hydroxyl group in the acids. Superior adhesive bonding to the Ni-Cr alloyed metal substrate was achieved via a heating process at 150 °C, and high average tensile strengths of ∼80 MPa were obtained by using mixtures of BOEs and dl-tartaric acid. This highly adhesive property was achieved not only by polycondensation of BOE-hydrolyzates and the carboxylic acids, but also by polyaddition of BOEs and the carboxylic acids.