Abstract
High‐resolution proton magnetic resonance and infrared spectra of poly(vinyl formal) were studied in comparison with those of the model formals obtained from stereoisomers of pentane‐2,4‐diol and heptane‐2,4,6‐triol in order to learn spectral changes due to differences of the steric structures of the polymer. In the NMR spectrum of __trans__formal obtained from dl diol or dl,dl (syndiotactic) triol, all proton signals were well interpreted by assuming a rapid chair‐chair inversion of the formal ring. On the other hand, no such inversion was observed spectroscopically in cis‐formal obtained from the meso diol or meso,meso (isotactic) triol, and the cis‐formal ring was supposed to take a diequatorial form preferentially. Consequently, dioxymethylene protons gave a single peak (equivalent) in trans‐formal and an AB quartet (nonequivalent) in cis‐formal. In the spectra of poly(vinyl formal), the dioxymethylene signal was an overlap of the singlet and quartet in dimethylsulfoxide solution. Observations of the spectra of various poly(vinyl formals) obtained from poly(vinyl alcohols) of different tacticities and study of temperature dependence of the signal have shown that the singlet and quartet are attributed to trans‐ and cis‐ formals, respectively, in the polymer spectrum also. In the infrared spectra of poly(vinyl formals), the 800 and 785 cm^‐1^ bands were found to be related to cis‐ and trans‐formal rings respectively. A linear relationship was confirmed between D~785~/D~800~ and trans/cis ratios determined from the peak intensities of the dioxymethylene proton signals.