CH₂ Rocking vibrations and the structure of polyethylene glycols

The infrared absorptions of polyethylene glycols of various degrees of polymerization from a 14‐mer to a 90‐mer in pure liquid state, in benzene solutions, and in thin solid films were recorded. The data bridge with gradual changes of spectral patterns the transition between the absorptions due to CH 2 ‐rocking modes of lower members and those of crystalline high polymer of this series. This enables one to make unequivocal assignments of observed frequencies to the normal modes of an O(CH 2 ) 2 O unit capable of assuming either gauche or trans configuration. The band at about 845 cm. −1 is a crystalline band, while those at about 885 and 863 cm. −1 are amorphous bands. The absorption at about 948 cm. −1 splits into doublets in crystalline high polymers. The gradual changes in spectral features with‐degree of polymerization show how the helical structure of high members of this polymer series changes into less regular structures of the lower members.