Abstract
Deuterium n.m.r. has been used to follow the molecular dynamics of three polyester materials over a temperature range of −150°C to 150°C. Two of the materials are liquid crystalline copolymers, one of perdeuterated hydroxybenzoic acid and hydroxynaphthoic acid and the other of hydroxybenzoic acid, isophthalic acid and perdeuterated hydroquinone. The third sample is crystalline poly(ethylene terephthalate) (PET) in which the benzene rings are deuterated. At the lowest temperatures examined all three materials give n.m.r. lineshapes characteristic of little molecular motion. On heating the liquid crystalline materials, the onset of motion is observed, first in the form of 180 o flips and then unrestricted rotation about the polymer axes. The PET spectra show a small degree of 180 o ring flipping to be taking place above 100°C, but most of the motion is in the form of near random motion that comes to dominate at 150°C. The results confirm the relatively stiff rod-like nature of the liquid crystalline polymers in comparison to the more flexible PET.
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