STUDY OF RELAXATION TRANSITIONS IN SOME AROMATIC POLYESTERS

Abstract

The spin probe method was used to systematically study the main relaxation transitions of rigid-chain glassy polymers in a wide temperature range using spin probes of different sizes using polysulfone as an example. In the main relaxation region of aromatic polyesters, two inflections were found using the spin probe method. The two inflections found in the temperature dependence of the rotation correlation time are the result of unfreezing of segmental mobility in regions with different packing of segments. It was shown that the high-temperature inflection corresponds to the defrosting of the cooperative-type segmental mobility (α-transition), and the inflection at a lower temperature corresponds to the β-defrosting of the segmental mobility of the local type (the α'-process). To explain the nature of this transition, a theoretical model of the polymer was used, where it is assumed that different levels of supramolecular organization are possible in amorphous polymers, i.e. the existence of more ordered and more densely packed regions, which alternate with looser and less ordered regions. The influence of various factors on the position of the α'-transition on the temperature scale is investigated. The choice of the probe volume on the basis of a strictly substantiated model of its motion made it possible to reveal the relationship between the rotational motion of the probe and the motion of individual segments of the amorphous polymer below the glass transition temperature.

Keywords

• polyester
• polysulfone
• polycarbonate
• spin probe method
• glass transition temperature
• pre-carbonate temperature