Thermal crystallization from the glassy state was investigated for iso
tactic polystyrene (iPS) at three temperatures (140 degrees C, 170 deg
rees C, and 200 degrees C) for different times. The crystallized sampl
es were analyzed by x-ray diffraction, differential scanning calorimet
ry (DSC), and transport properties of dichloromethane vapor. X-rays an
d DSC give very similar values of crystallinity. At variance, sorption
measurements indicate a fraction of amorphous phase much lower than t
he previous. The presence of a mesophase, impermeable to the vapors at
low activity, was hypothesized. Its value is constant for annealing a
t 140 degrees C, whereas it decreases with time at 170 degrees C and 2
00 degrees C, in correspondence with an increase of the crystalline fr
action.