Infrared spectra of poly(ethylene 2,6-naphthalate) and some related polyesters

Infrared spectra of some poly(methylene terephthalates) and some poly(methylene 2,6-naphthalates) were compared. To interpret the spectral changes during drawing and heat treatment, the concept of rotational isomerism of the ? O-(CH₂)_M-O? part, which was fairly successful in poly(ethylene terephthalate) (C₂T), was tried to apply to the polyesters other than C₂T. Also, the bands originated from a benzene ring and from a naphthalene ring were distinguished. Poly(ethylene 2,6-naphthalate) (C₂N) has some bands behaving differently from those of other polyesters. This would be due to the existence of certain intermolecular interactions arised from tight packing of the molecules in the crystal of C₂N.