The infra-red spectrum and molecular structure of poly(cyclohexane 1,4-dimethylene terephthalate)

Abstract

Films of poly(cyclohexane 1,4-dimethylene terephthalate) ( pcht) that had been drawn and crystallized in various ways were examined by normal and polarized infra-red radiation in the range 5000 cm −1 to 20 cm −1. The trans pcht isomer is centro symmetric in the crystalline phase. The space group of the monomeric unit is P, 1 isomorphous with C i symmetry. The cis-polymer is not centro symmetric, the space group is probably P1 isomorphous with C 1 symmetry. A number of model compounds were also studied. The terephthalate framework is expected to behave similarly to that in polyethylene terephthalate, the terephthalate conformation being more affected by changes in molecular orientation and crystallization than by those in the conformation of the diol fragment. In the same way the terephthalate framework is expected to be centro-symmetric and planar (symmetry V h  D 2 h ) only when highly crystallized and oriented. In amorphous regions, out of plane bending of CO groups causes lowering to C 2 v symmetry. The spectral changes in cis and trans pcht, as would be expected from the above, are very similar to those of pet. There is little difference between cis and trans isomers in the same state, apart from a strong band at 630 cm −1 in both Raman and infrared spectra of the cis isomer, that is practically absent in the trans. On change of state, however, trans substituted isomers do show significant intensity changes, in contrast to cis isomers.