Abstract
AbstractVolume‐temperature relations of six kinds of epoxy resin‐acid anhydride composite and different curing times are discussed on the basis of free‐volume and occupied‐volume concepts. The specific volume Va at a fixed temperature above Tg decreases linearly with increasing Tg, but the specific volume Vb below Tg increases linearly. The specific volume Vg at Tg increases linearly with increasing Tg. The relation between Tg and log crosslinkage is linear except in the final stage of the curing process. The slope B of the Vg‐Tg relation is obtained from the iso‐free‐volume theory of glass‐transition phenomena as B = Voαb(1 – ΔVo/Vf · Vf/Vo · αa – αb/αb), where Vo is the occupied volume, Vf the free volume, αa – αb the thermal expansion coefficient of free volume, αb the thermal expansion coefficient of occupied volume; Vo is the sum of the two components Vo and Vo, where Vo is the occupied volume in the strict sense and ve is the empty volume into which polymer chains cannot flow. The equation predicts qualitatively the observed value of B.
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