Design and Modulation of Negative Thermal Expansion for Epoxy Polymers

Modulating the coefficient of thermal expansion (CTE) and realizing low or negative thermal expansion (NTE) for epoxy polymers are challenging issues. In this study, we developed an effective strategy to prepare epoxy polymers with an NTE performance. A novel motif DBCOD-NH₂ based on the dibenzocyclooctadiene (DBCOD) was designed, synthesized, and utilized as a curing agent for several commercial epoxy resins. DBCOD-NH₂ suppressed the thermal expansion of the epoxy polymer due to the conformational transition of DBCOD from boat to chair, resulting in low or negative CTE. The AFG90-based polymer showed the most significant thermal contraction behavior (-43.6 ppm/K, 40-80 °C) in the glassy state due to the high DBCOD content, chain rigidity, and cross-link density, which resulted from the high epoxy values, rigidity, and functionality of AFG90 resins. The structure-property interactions were examined and applied to modulate the NTE of epoxy polymers. Our findings are useful for the regulation of thermal expansion and the preparation of materials with desired CTE values.