Abstract
On the basis of thermal analysis it is suggested that the crystals of aliphatic nylons exhibit conformational disorder above the glass transition. The disorder begins gradually at about room temperature and is evidenced by an increase of the heat capacity to values higher than that of the melt. The specific case of nylon 6.6 is investigated by thermal analysis and x-ray diffraction. The onset of conformational disorder can be clearly separated from premelting. It is shown that the Brill transition, as defined by the merging of the two main peaks in the x-ray diffraction pattern, occurs gradually and is thermal-history-dependent. The transition is not a first-order one, it is only an incidental thermal effect, associated with a packing change in the crystal. In solution-crystallized (sc) samples this change is related to a distinct endothermic peak, while in melt-crystallized (mc) samples it is related to a broad endotherm.
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