High performance epoxy resin with ultralow coefficient of thermal expansion cured by conformation-switchable multi-functional agent

Epoxy resins with low or negative thermal expansion have been widely searched for a long time owing to their great potential application in aerospace and microelectronics field. For the filler/epoxy resin composites, one key parameter of epoxy resins is to have suitable low coefficient of thermal expansion (CTE) to match with the fillers, however, it still remains a big challenge. In this work, we design and synthesize a new kind of conformation-switchable curing agent that contains dibenzocyclooctadiene (DBCOD) unit, named as cis-diamine-DBCOD. The epoxy resins cured by cis-diamine-DBCOD possess controllable CTE from negative to positive due to the conformational switch of DBCOD units, and the CTE can be tuned by the DBCOD content. We demonstrate the DBCOD units can undergo conformational change from boat to chair conformer with the rise of temperature based on the theoretical calculation and experimental results. Several commercial epoxy resins cured by cis-diamine-DBCOD also exhibit low CTE (around 10 ppm/K), reflecting the universality of the conformation-switch curing agent. Compared with conventional arylamine curing agents, the epoxy resins cured by cis-diamine-DBCOD possess higher Tg (218 °C) from DMA, which has 49 °C increase comparing with the corresponding epoxy resin with similar elongation at break. Meanwhile, the cured epoxy resin has superior mechanical properties, the tensile strength has 46.3 % increase. Therefore, the cis-diamine-DBCOD as a multi-functional conformation-switchable curing agent endows the cured epoxy resin with high dimension stability, thermal and mechanical performances for the specific applications.