Here T g,∞ is the glass transition temperature for an ideal polymer chain of infinite length, K is a proportionality constant, and M n is the number average MW of the polymer. The equation reflects that a polymer of low MW has more free volume than a polymer of high MW, since the low MW polymer must have a greater concentration of chain ends for the same mass of sample. Consequently, an increase in the concentration of chain ends is accompanied by a decrease in T g . For a given polymer, an increase in chain end concentration directly affects the average packing density of the polymer, and the presence of end groups results in a decrease in the density of the configurational structure in proportion to 1/M n . For a given dispersity, the constant K is directly related to the free volume of the end groups of polymer chains.