No abstract

Changes in the distribution of local free volume in polystyrene glass during physical aging were measured by using photochromic probe molecules requiring different amounts of volume to photoisomerize.The fraction of local free volume in the size range 130-180 A3 is constant as the polystyrene molar weight decreases to a critical value between 34000 and 92000. At lower molar weights the fraction of local free volume in the size range 130-280 A3 decreases with decreasing molar weight. Physical aging in polystyrene glass reduces or leaves unchanged the fraction of local free volume larger than each probe needs to isomerize. During physical aging the greatest loss of local free volume occurs in the size range larger than 280 A3, but the amount of loss varies with annealing temperature. The temperature of maximum rate of loss is 20-25 "C less than Tg for polystyrene of 3970 and 9050 molar weight. In polystyrene of 573000 molar weight annealed 250 h at 30 "C, most of the loss of local free volume larger than 280 A3 occurs within the first 4 h.

No abstract

No abstract

No abstract