Crystallographic changes in cryogenically pulverized polymers.

Cryogenic pulverization of polymers in liquid nitrogen results in a variety of physical and chemical changes, of which crystallographic are among the earliest. These have been investigated in detail for isotactic polystyrene using X-ray and calorimetric techniques. Amorphization was found to occur rapidly, but with concomitant decreases in crystallite sizes of only a limited extent. These changes can to a large degree be reversed upon annealing at high temperature. Similar behavior is seen also in other polymer possessing stronger intermolecular cohesion, such as polyesters and polyamides.