Polymer, Vol.44, No.26, 8025-8032, 2003
Effects of freeze-drying on the glass temperature of cyclic polystyrenes
The calorimetric glass temperature was measured for three cyclic polystyrenes with apparent molecular weights ranging from 4.0 x 10(3) to 195.5 x 10(3) g/mol for both bulk material and for samples freeze-dried from dilute solution. Freeze-drying from dilute solution was found to reduce the glass temperature by 7-14 K depending on the sample. These T-g depressions are 5-12 K greater than those found previously for freeze-dried linear polystyrene. Annealing at 403.2 and 443.2 K (130 and 170 degreesC) resulted in recovery of the T-g back to the bulk value with the time scales depending on both temperature and the magnitude of the T-g reduction; the low apparent activation energy dependence of the recovery of T-g precludes its being due to viscous flow. (C) 2003 Elsevier Ltd. All rights reserved.