Poly(ether urethane) flexible cyanate ester resins: Synthesis, characterization, and performance in commercial epoxy and polyurethane applications

A poly(ether urethane)‐based cyanate ester resin (PEUCER) with a biphenyl polyether backbone obtained from polymeric 4,4′‐diphenylmethanediisocyanate, bisphenol A, polyether polyols of three different molecular weights, and cyanogen bromide was synthesized to obtain a polymer with better functional and physical properties, such as adhesion, flexibility, and thermal stability. The synthesis of the poly(ether urethane)‐based 4,4′‐(oxybiphenyl propane) cyanate ester involved three steps: the formation of the poly(ether urethane) NCO‐terminated prepolymer, the formation of the OH‐terminated poly (ether urethane) prepolymer (PEU–PP), and the esterification reaction of cyanate to produce PEUCER. PEUCER was cyclotrimerized to yield a triazine‐ring‐containing polymer, which possessed better adhesion at high temperatures and better impact resistance. PEU–PP and PEUCER were characterized with wet chemical analysis, spectral methods, and thermal methods. PEUCER showed better performance with respect to thermal and adhesion properties with a single‐part polyurethane lamination adhesive and also showed better performance as a toughening agent in a two‐part epoxy laminate system.