ISSN:
0887-6266
Schlagwort(e):
Poly(oxy-1,4-phenyleneoxyxylyleneoxy-1,4-phenyleneoxyundecamethylene)
;
conformational disorder
;
liquid crystal
;
condis crystal
;
13C NMR
;
γ-gauche effect
;
DSC
;
entropy
;
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A thermotropic main-chain polyether based on bis(4-hydroxyphenoxy)-p-xylylene and 1,11-dibromoundecane has been studied by variable-temperature solid-state 13C NMR. Between isotropization and glass transition temperatures, the material can be identified to be semicrystalline, consisting of two conformationally and motionally distinguishable phases. The more mobile component is liquid-like and thus, can be attributed to an amorphous phase. In the more rigid component, the molecules have a conformationally disordered methylene sequence. In the low-temperature ordered phase approximately ⅔ of the carbon-carbon bonds are trans (t). Starting from the bond between the oxygen and the first methylene carbon, the bond conformations are: d—t—d—t—t—t—t—t—t—d—t—d, where d stands for disordered (i.e., it represents the common dynamic interchange between gauche and trans with an overall gauche content of perhaps 40%). The motion of the αα′-diphenoxy-p-xylylene unit consists mainly of 180° ring-flips, which cause no entropy increase relative to ordered phenylene groups in a crystal, but significantly changes the 13C NMR spectra. The central p-xylylene ring starts its flipping motion at a lower temperature than the two phenoxy rings. The high-temperature mesophase contains a methylene sequence of the bond conformations: d—t—d—d—d—t—t—d—d—d—t—d. Thus, the difference between the low-temperature and high-temperature mesophases consists of different degrees of conformational disorder. Thermal analysis seems to indicate that additional mesophases may be possible. © 1994 John Wiley & Sons, Inc.
Zusätzliches Material:
7 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/polb.1994.090320414
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