Structural Studies of Polyethers, [–(CH2)m–O–]n. VII. Infrared Spectra of Polyoxacyclobutane

Abstract

Polarized infrared spectra of the three modifications of polyoxacyclobutane [–(CH2)3–O–] n have been measured in the region from 4000 to 80 cm−1. The selection rules for modifications I, II, and III are derived under the factor groups isomorphous to C 2υ , C s , and D 2 , respectively. The normal vibrations have been calculated for these modifications using the GFmatrix method with the Urey–Bradley‐type force field, and the vibrational assignments of the absorption bands have been given. For modification I (planar zigzag form), the CH2 rocking vibrations split into three modes which correspond to the modes with the phase differences of 3π / 4, 2π / 4 , and π / 4 of a simply coupled oscillator model consisting of three methylene units, respectively. The observed frequencies have been found to fit the calculated dispersion curve for the rocking–twisting branch (ν 8 ) of the polymethylene chain. Similar behavior in the rocking modes occurs also in the cases where the O–CH2–CH2–CH2–O group assumes the TG (modification II) or GG (modification III) conformation. Thus, the difference in the skeletal conformation gives rather little effects on the rocking modes of the polyoxacyclobutane molecule.