| Abstract |
The molecular mobility of poly (propylene glycols) with molecular weights between 2000 and 18,200 g mol(-1) was studied in the amorphous solid state, in the region of the glass transition and in the rubbery state; the experimental techniques used were differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). It was found that the glass transition temperature increases slightly with MW and tends to a limit value: T-gDSC = -67 degrees C, T-gTSDC = -73 degrees C. The different types of molecular mobility were analyzed: below T-g the secondary relaxations, and above this temperature the normal mode, were characterized in detail using TSDC; in the glassy transformation region, around T-g, the main relaxation was analyzed by both DSC and TSDC. It was found the dynamic fragility, m, behaves as independent of the molecular weight in the studied range: m(DSC) = 74 and m(TSDC) = 92. The TSDC results also show that, without influencing the kinetics of the segmental relaxation, the increase in molecular weight slows down the chain relaxation. |
