The impact of aging PVC/Aliquat 336 polymer inclusion membranes (PIMs) on their thermomechanical properties and heavy metal extraction performance was investigated. The results show that freshly prepared PIMs contain residual tetrahydrofuran (THF) which was used as the solvent for membrane manufacture. Removal of some residual THF by membrane aging resulted in notable changes in the thermomechanical properties of the PIMs. By aging the membrane for 1 week at 40°C, the glass transition increased from 42 to 55°C. In addition, while the melting temperature (Tm) of the Aliquat 336 component could not be determined for freshly prepared PIMs, the aged membrane showed a clear Tm value of −19°C. Metal extraction capacity was not affected by membrane aging.