The insertion of oligo(tetraflouroethene) segments into the main chain of poly(aramide)s and poly(amide imimide)s is accompanied by a decrease of the glass temperature. The decrease is strictly related to the number of CF2-units and is the same for both poly(aramide)s and poly(amide imide)s. The absolute glass temperature depends, however, on the initial structures of the monomeric units. As a consequence ’mastercurves’ can be constructed by shifting the individual Tg vs. number of CF2-units curves along the temperature axis. A detailed analysis of the data indicates that besides the Tg - mass/flexible’ bond of monomeric unit criterion additional volume and interaction dependant packing effects have to be considered for an accurate prediction of the glass temperatures of polymers.