Thickness–direction thermal‐expansion measurements

Thermal expansivity in the thickness direction for three commercially synthesized and processed polyimide films, PMDA–ODA, BPDA–ODA, and BPDA–PDA, have been measured. The expansivity in the thickness direction is significantly higher than that in the in‐plane direction. The observed anisotropy is explained by the orientation texture of the films. The differences in the expansivity is explained by the molecular conformation of the chain. The latter is calculated by energy minimization excluding the entropic effects. The conformation analysis reveals a helical‐like conformation for ether‐linkage‐containing chains, which explains, which explains the higher expansivity in PMDA–ODA as opposed to BPDA–PDA. The possibility of helical conformation in PMDA–ODA and BPDA–ODA is novel. © 1992 John Wiley & Sons, Inc.