CROSS-POLARIZATION MAGIC ANGLE SPINNING C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY OF LINEAR DEXTRAN CRYSTALLIZED FROM POLY(ETHYLENE GLYCOL) WATER SOLUTION AT A HIGH-TEMPERATURE

The solid-state structure of a synthetic linear dextran, which was crystallized at 160 °C from a mixture of water and poly(ethylene glycol), has been investigated by CP/MAS13C NMR spectroscopy. The CP/MAS13C NMR resonances narrow upon absorbing water without any change in chemical shifts, suggesting that some distortion of the molecular chains, which is produced by drying, may be relaxed upon the sorption of water. Each resonance line of wet dextran contains two components with13C spin-lattice relaxation times, T1C, of 170-203 and 8.0-11.4 s, which correspond to the crystalline and noncrystalline components, respectively. When the difference in T1C is used, separate spectra of the crystalline and noncrystalline components have been obtained. The line-shape analysis shows that the crystalline spectrum consists of six doublets with a 1:1 ratio corresponding to six carbon sites. These six doublets may originate from two different electronic environments produced by two different packing arrangements. The degree of crystallinity is approximately estimated to be 46% by the line-shape analysis, and the lamellar thickness is determined as 60 Å from SAXS. From these values the crystalline and noncrystalline thicknesses are assumed to be of the orders of 28 and 16 Å, respectively. © 1990, American Chemical Society. All rights reserved.