Free-volume hole distributions of polypropylene

Positron annihilation spectroscopy (PAS) has been applied to study the free-volume hole distributions of a semi-crystalline polypropylene polymer as a function of pressure and a function of age after the pressure is released. The free-volume hole distributions as determined from the ortho-positronium lifetime distributions have maxima of diameters varying from 6 angstrom to 2 angstrom as pressure increases from 0 to 14.7 kbar. The authors also found that the hole distributions have been significantly changed when the polymer is released from high pressure. Applications of PAS to understand material properties of polymers from free-volume results are discussed