ISSN:
0887-6266
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Thin films of spin-probed and spin-labeled poly(methyl methacrylate) (PMMA) have been examined by electron spin resonance (ESR) in the temperature range of 77-520°K. The rotational correlation times of nitroxides used as spin probes and labels have been determined as a function of temperature from which activation energies are also determined. The nitroxide rotational times are found to strongly correlate with local segmental and side-chain motions of the host PMMA matrix. Five discrete molecular motions are detected in PMMA along with their activation energies as measured: side-chain CH3 rotation (1 Kcal/mol), main-chain CH3 rotation (2 Kcal/mol), ester side-chain COOCH3 rotation around the C—C bond (4 Kcal/mol), main-chain C—C bond rotation (6 Kcal/mol), and side-chain OCH3 rotation around the C—O bond (18 Kcal/mol). The activation energies determined by ESR are consistent with the potential-energy barriers calculated theoretically for various rotations in PMMA. It is concluded that the probe and label rotational motions do respond to localized, small-scale segmental and side-chain motions of host polymers but are relatively ineffective in response to the large-scale segmental motion with an activation energy larger than 20 Kcal/mol in the case of PMMA.
Zusätzliches Material:
18 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/polb.1987.090250413
Permalink