Pulsed electron nuclear double resonance study of molecular motions of radicals in a high-strength liquid-crystalline polymer

✍ Scribed by M. Hubrich; G.G. Maresch; H.W. Spiess

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 494 KB
• Volume: 218
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(93)e1459-t

✦ Synopsis

Radicals in a liquid-crystalline copolyester are studied by pulsed electron paramagnetic resonance (EPR) and pulsed electron nuclear double resonance (ENDOR). For the first time transient ENDOR techniques are used to investigate molecular motion of radicals in a disordered solid. The nuclear phase memory relaxation of hypefine coupled protons is measured in a temperature region between 250 and 350 K in the solid state. Remarkably, the relaxation rate increases linearly rather than quadratically with the strength of the hypertine coupling IA, I. This results from a thermally activated process, characterized by small-angle flue tuations of radicals with an amplitude of the order of lo. The corresponding activation energy of 24 kJ/mol indicates that the radicals are chain ends in the polymer.