New contributions from thermal and dielectric techniques to the understanding of the dynamic properties of medium to long chain poly (propylene glycols)

Abstract

AbstractThe 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: TgDSC = −67°C, TgTSDC = −73°C.The different types of molecular mobility were analyzed: below Tg the secondary relaxations, and above this temperature the normal mode, were characterized in detail using TSDC; in the glassy transformation region, around Tg, 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: mDSC = 74 and mTSDC = 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.