STRUCTURE, CONFORMATION, AND MOTIONS OF POLY(ETHYLENE OXIDE) AND POLY(ETHYLENE GLYCOL) IN THEIR UREA INCLUSION-COMPOUNDS

X-ray diffraction and FTIR and C-13 NMR spectroscopies have been utili zed to observe the inclusion compounds (ICs) formed by poly(ethylene o xide) (PEG) and low molecular weight poly(ethylene glycol) (PEG) oligo mer with urea (U). We have confirmed that PEO-U-IC formed from solutio n has a trigonal crystal structure, while recrystallization from the m elt produces a hexagonal PEO-U-IC. PEG-U-IC apparently adopts a crysta l structure different from the trigonal and hexagonal forms of PEO-U-I C, and single crystals of PEG-U-IC are currently under investigation b y X-ray diffraction. The conformations of PEG. and PEG chains in their U-ICs appear similar to the TGT bulk crystalline conformation, while the all-trans conformer does not appear to be consistent with either t he FTIR or the C-13 NMR observations. For solution-formed PEO-U-IC in the trigonal crystal structure, where one-third of the urea molecules are hydrogen-bonded to the PEO chains and reside in the channels, the mobility of the included PEO chains is similar to that of the bulk cry stalline PEG. This is quite different from the usual observations made on hexagonal polymer-U-ICs, where spin-lattice relaxation times obser ved for the carbon atoms of the included polymers are much reduced (of ten more than 1 order of magnitude) from those observed for the same p olymer in their bulk crystals. It is proposed that the direct involvem ent of the urea molecules in the trigonal channels of PEO-U-IC with th e included PEO chains is the source of their reduced mobility.