N. Vasanthan et al., STRUCTURE, CONFORMATION, AND MOTIONS OF POLYTETRAHYDROFURAN (PTHF) INTHE HEXAGONAL FORM OF THE PTHF-UREA INCLUSION COMPOUND, Journal of polymer science. Part B, Polymer physics, 33(9), 1995, pp. 1385-1393
Combination of differential scanning calorimetry, x-ray diffraction, F
ourier transform infrared, and C-13 nuclear magnetic resonance observa
tions made on the crystalline inclusion compound (IC) formed between p
olytetrahydrofuran (PTHF) and urea (U), together with their comparison
to identical observations performed on bulk semicrystalline samples o
f PTHF, have permitted an analysis of the conformations, motions, and
environments available to PTHF chains in both solid-state phases. The
isolated PTHF chains occupying the narrow channels of the PTHF-U-IC ar
e highly extended, though small rotational deviations averaging 24 deg
rees from the nearly all trans, planar zig zag conformation of bulk cr
ystalline PTHF chains produce some significant differences in their be
haviors. PTHF chains in PTHF-U-IC possess much greater mobility than b
ulk crystalline PTHF chains as evidenced by C-13 spin lattice relaxati
on times, T-1, 50 times shorter (1.5 s) than observed for bulk crystal
line PTHF chains (75 s). FTIR observations are consistent with very li
ttle specific interaction between guest PTHF chains and host urea matr
ix molecules and result in similar spectra for bulk and IC PTHF, excep
t for the presence of the CH, rocking vibration band at 745 cm(-1) obs
erved for bulk PTHF. The absence of this band in the IC PTHF can be un
derstood by considering the symmetry of the all trans, planar zig zag
conformation of bulk crystalline PTHF chains, which prevents the CH, r
ocking mode from coupling with skeletal stretching and bending modes a
s occurs in the nonplanar, helical PTHF chains in PTHF-U-IC. (C) 1995
John Wiley and Sons, Inc.