The Impact of Polyethersulfone Hydroxyl End Groups on the Properties of Epoxy Resin

ABSTRACT The work presents a comprehensive study of the influence of polyethersulfone (PESU) with and without hydroxyl end groups on the structure and properties of epoxy resin in its initial state and upon its curing with 4,4'‐diaminodiphenylsulfone. The presence of hydroxyl end groups in the thermoplastic results in two effects: an improved crosslink density and a reduced activation energy for the initial curing stage by 25 kJ·mol −1 . The glass transition temperature has been determined for epoxy polymers that contain polyethersulfone with both open and blocked hydroxyl end groups. Phase equilibria in the initial systems and during the curing process were investigated via optical interferometry. It has been established that the systems are characterized by amorphous stratification diagrams, with a lower critical solution temperature of 110°C or 140°C for PESU with open and with blocked end groups, respectively. Curing with 4,4'‐diaminodiphenylsulfon at 180°C leads to the formation of homogeneous systems. The data obtained in this study will be useful for developers of composite binders and technologists working with high‐temperature compounds that exhibit predictable properties due to their homogeneous structure in the cured state.