Dielectric relaxations in linear aliphatic polyesters

Abstract

Molecular motions in a series of linear aliphatic polyesters [poly(ethylene adipate), poly(ethylene sebacate), poly(hexamethylene sebacate), and poly(decamethylene 1,16‐hexadecanedicarboxylate)] were studied by dielectric measurements. Two loss maxima were observed for each polymer in the temperature range from −196 to about 60°C and in the frequency range from 110 to 105 Hz. The loss maxima of these polyesters, lying between −17 and −38°C at 110 Hz (β‐relaxation), are due to the micro‐Brownian motions of amorphous main chains. It was found that these β‐relaxations are well described by the WLF equation. The loss maxima in the range from −88 to −109°C at 110 Hz (γ‐relaxation), are attributed both to local mode motions of main chains in the amorphous region and to motions of the polar groups involved at the chain ends. For the β‐relaxation, no simple relation between the methylene sequence length and the loss peak temperature was found. Furthermore, as the methylene sequence length decreased, the effective dipole moment of the polyesters increased gradually. These facts were explained in terms of interchain dipole attraction.

Pulsed NMR in Linear Aliphatic Polyesters

“…The rand ,8-relaxations have been attributed to the local mode motion and micro-Brownian motion, respectively, in the noncrystaiiine region. 4 Present NMR results also support these conclusions, since the T2• component airses from the noncrystalline regions. The value of T2• of the 2-8-MG and 10-16-MG on the high-temperature side of the r-transition are 17 and 27 p,sec, respectively.…”

“…Details of the preparation are given in a previous paper. 4 Bulk crystallized samples (MG) were prepared by hot pressing at above their melting temperature and cooled slowly to room temperature in vacuo.…”

“…The value of T2• of the 2-8-MG and 10-16-MG on the high-temperature side of the r-transition are 17 and 27 p,sec, respectively. The expression for the T2 depends on the model for molecular motion, but if we assume that the relaxation is due to reorientation of the dipole-dipole vector, we can then write 10 •P 300 (4) where M 2 is the second moment of the motional phase and r is the reorientational correlation time of the dipole-dipole vector. Equation 4 has assumed that W 0 r » 1, where W 0 is the nuclear precession angular velocity of 3.8 x 10 8 rad/sec, and this assumption is valid when T2 « T1.…”

“…Linear aliphatic polyesters are particularly appropriate for elucidating this relation, since the morphological regularity and simplicity of single crystals of the polyesters have been correlated with chemical structure of the polymer. 2 ' 3 In a previous paper, 4 we reported the dielectric relaxation behavior of some linear aliphatic polyesters. In the ,a-relaxation which corresponds to the glass transition of the polyesters, the loss peak tempearture and the effective dipole moment of the motional unit are correlated with the chemical structure of the polymer.…”

The chemistry, manufacture and tensile behaviour of polyester fibers

“…The lower the values of T g the lower will be the energetic barriers hindering mobility in the amorphous phase. A decrease in T g is affected by [47]:…”