Conformational analysis of poly(oxymethylene)

The conformational energies of the lower members of poly(oxymethylene), 2,4‐dioxapentane and 2,4,6‐trioxaheptane were estimated by the empirical force field method. The gauche states of the internal rotation around the skeletal CO bonds were successfully predicted to be of lower energies in both molecules. In order to calculate the unperturbed dimension and dipole moment of poly(oxymethylene), rotational isomeric state approximations were made by using the results obtained from the force field calculations on 2,4,6‐trioxaheptane. The first‐order interaction energy was estimated to be a large negative value, and the second‐order interaction energies for g ± g ± had non‐zero values. Although these parameters were significantly different from those estimated earlier, they reproduced the observed results fairly well. Thus the “gauche effect” of poly(oxymethylene) was explained by taking account of the effects contributed by the lone pairs of electrons on the oxygen atoms. As adopted in this study, the procedure joining the empirical force field method to the statistical mechanical one was shown to be effective for the investigation of many sorts of configuration‐dependent properties of chain molecules.