Exposure of polyamides to heat and oxygen may cause changes in the physical and chemical characteristics due to thermal oxidative degradation [43] and thus changes in the mechanical properties. Prolonged annealing at a high temperature results in undesirable changes in the degree of crystallization and in the end groups, and may cause inter- and intramolecular transamidation reactions, chain scission and crosslinking [44-491 The electrical resistance technique is capable of studying the effect of annealing (in air at various temperatures below the melting temperature for various lengths of time) on the glass transition and melting behavior.