THE CHAIN CONFORMATIONS OF A POLYETHER BASED ON BIS(4-HYDROXYPHENOXY)-P-XYLYLENE AND 1,11-DIBROMOUNDECANE (HPX-C-11) IN ITS MESOPHASE STATES, DERIVED FROM C-13 NMR

A thermotropic main-chain polyether based on bis (4-hydroxyphenoxy)-p- xylylene and 1,11-dibromoundecane has been studied by variable-tempera ture solid-state C-13 NMR. Between isotropization and glass transition temperatures, the material can be identified to be semicrystalline, c onsisting of two conformationally and motionally distinguishable phase s. The more mobile component is liquid-like and thus, can be attribute d to an amorphous phase. In the more rigid component, the molecules ha ve a conformationally disordered methylene sequence. In the low-temper ature ordered phase approximately 2/3 of the carbon-carbon bonds are t rans (t). Starting from the bond between the oxygen and the first meth ylene 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 overal l gauche content of perhaps 40%). The motion of the alpha,alpha'-diphe noxy-p-xylylene unit consists mainly of 180-degrees ring-flips, which cause no entropy increase relative to ordered phenylene groups in a cr ystal, but significantly changes the C-13 NMR spectra. The central p - xylylene ring starts its flipping motion at a lower temperature than t he two phenoxy rings. The high-temperature mesophase contains a methyl ene 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 conformat ional disorder. Thermal analysis seems to indicate that additional mes ophases may be possible. (C) 1994 John Wiley & Sons, Inc.