Thermal expansion of epoxide-amine networks in the glassy state

The dilatometric curves of 21 epoxide–amine network samples made from five distinct epoxide–amine pairs, with variable amine/epoxide functional ratio values for three of these pairs, were recorded in the 200 K to Tg (glass-transition temperature) − 50 K temperature range. The curves display a quasiparabolic shape consistent with an expansion law derived from a thermodynamic study [Bongkee, C. Polym Eng Sci 1985, 25(18), 135]: where V and V0 are the volumes at T and 0 K, respectively, and A is a coefficient that varied for the studied samples between 2.5 × 10−7 and 5.0 × 10−7 K−2. A tentative study of the structure–property relationships in this field revealed that A does not depend significantly on the crosslink density, the cohesive energy density, the Tg, or the local mobility. In contrast, A seems to be sharply related to the chain flexibility, which essentially depends on the aromatic content in the studied structural series.