Conformational Characteristics of Poly(tetramethylene oxide)

Conformational characteristics of poly(tetramethylene oxide) (PTMO) have been investigated on the basis of the conformational energies evaluated for its monomer model 1,4-dimethoxybutane (DMB) from the ab initio molecular orbital (MO) calculations at the second-order Møller−Plesset correlation level with the 6-31+G* basis set. The reliability of our conformational energies was examined by comparison between calculations and observations of NMR vicinal 13 C− 1 H and 1 H− 1 H coupling constants of DMB and the characteristic ratio and dipole moment ratio of PTMO. Then the C−O bond dipole moment ( m C - O ) for the rotational isomeric state analysis of polyethers was determined from the MO and 1 H NMR data reported previously for 1,2-dimethoxypropane, a monomeric model compound of poly(propylene oxide). The optimal m C - O value was obtained as 1.18 D. The conformational energies reproduced the experimental observations very well. The relationship between the conformational characteristics and crystal structures of polyethers [−(CH 2 ) y −O−] x ( y ≥ 4) is also discussed.