Local dynamics in a thermotropic terpolyester as revealed by dynamic mechanical analysis, ²H NMR and dielectric spectroscopy

Abstract

+t Dynamic mechanical, 'H NMR and dielectric spectroscopy techniques were used to identify the nature of the local motions involved in the secondary relaxations of a thermotropic aromatic terpolyester prepared from para-hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted B, y, arid 6, were detected. A B relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude x-flip processes observed by 'H NMR. Correlated motions of the para-substituted rings and adjacent carbonyl groups may also participate in the /?process. Then, at lower temperatures, a y process is detected by both dielectric and dynamic mechanical experiments. It is assigned to small amplitude oscillations of the isophthalic acid units of the HBA33 polymer. At high temperatures, a heavy overlap ofbroad rate distributions for the /? and y processes observed in the measurements precludes a more detailed analysis. A dielectric relaxation, denoted 6 relaxation, is observed at very low temperatures. It likely comes from motions of a very small number of water molecules trapped in the structure of the terpolyester.

The influence of annealing on thermal transitions in a nematic copolyester

“…6 kcal/mol, indicating that limited uncorrelated motions of very small groups are involved. 45 The preexponential factors resulting from these data fits increase with increasing temperature.…”

Phenyl ring dynamics and chain reorientation in liquid crystal polymers: A deuteron spin relaxation study

“…15,16 Most studies of phenyl ring dynamics in polymers have focused on the amorphous and crystalline states and suggest that the motion may be related to the secondary relaxations commonly observed by dynamic mechanical and dielectric relaxation spectroscopy. [15][16][17][18] Although there is now broad agreement that the phenyl rings undergo both fast low amplitude librational motion in the vicinity of the potential minima as well as slower -flips between these minima, the underlying physical mechanism by which this process occurs remains unclear and different researchers have invoked quite different interpretations of the observed distributions of correlation times and jump angles. 14,19 The principal aim of this article is to present a detailed analysis of intramolecular phenyl ring dynamics, based on a general diffusion model, 13 and compare the model predictions with results of deuteron ( 2 H) spin relaxation experiments conducted on a liquid crystal polymer ͑LCP͒ in the smectic A and nematic mesophases.…”