A possible mechanism of small molecule transport in glassy polymer membranes containing configurational free volume (i.e., triptycene moieties) is proposed. To this aim, a family triptycene-containing polybenzoxazoles (TPBOs) exhibiting systematically varied molar amount units, ranging from 25% to 100%, was selected perform light gas (N 2 , CH 4 and CO ) fundamental sorption-transport study. Th...