Secondary relaxation processes in polyethylene terephthalate–additive blends: 2. Dynamic mechanical and dielectric investigations

Abstract

Dynamic mechanical and dielectric analysis have been used to examine the effects that low molecular weight additives have upon the secondary relaxation processes in polyethylene terephthalate. In each of the polymer/additives blends examined one main secondary relaxation peak, known as the β peak has been observed below the glass transition temperature. It would, however, appear from the dielectric and mechanical results that the β peak consists of two different relaxation processes, one on the high temperature side and one on the low temperature side of the peak. A closer examination of these relaxation processes suggests that the high temperature side of the peak is due to phenyl ring flips, whereas the low temperature side is due to the motion of the carbonyl groups. In addition, it would appear that the activation energy and the enthalpy of the phenyl ring flips are both considerably higher than that of the carbonyls. Finally, when low molecular weight additives were blended into the polymer it was observed that only the high temperature side of the peak was suppressed and that the low temperature side remained virtually unaltered. This would indicate that although the additives suppress the motion of the phenyl rings, they have little effect upon the motion of the neighbouring carbonyl groups.