Origin of Heterogeneous Relaxation in a Random Liquid Crystal Thermoset Copolyester

Autor:	Theo J. Dingemans, Gordon J. Kearley, Olga Kruglova, John A. Stride, Fokko M. Mulder
Rok vydání:	2004
Předmět:	Materials science Polymers and Plastics Characteristic length Condensed matter physics Organic Chemistry Relaxation (NMR) Copolyester Inorganic Chemistry Liquid crystal Picosecond Polymer chemistry Materials Chemistry Dispersion (chemistry) Constant (mathematics) Glass transition
Zdroj:	Macromolecules. 37:9855-9860
ISSN:	1520-5835 0024-9297
DOI:	10.1021/ma0486849
Popis:	The 73/27 random copolyester based on 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) shows a fast, dispersed relaxation process on the picosecond time scale. The underlying motion is difficult to determine unambiguously, but the data are consistent with translation of chain segments in a direction that is perpendicular to the chain direction. As the temperature is increased from the beta transition (303 K) to the glass transition, Tg (381 K), the dispersion stays constant and the average relaxation time increases slightly. At Tg the dispersion increases abruptly to a new constant value, and the average relaxation time increases noticeably with temperature up to the nematic melt transition, Tm (553 K). This unusual behavior is probably connected to the appearance of a slow relaxation process that becomes discernible above Tg. The characteristic length of this slow process remains constant between Tg and Tm at a value that corresponds to the interchain spacing close to Tm. This observation...
Databáze:	OpenAIRE
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