Infrared spectra and regular sequence lengths in isotactic polymer chains

In order to elucidate the relationship between IR‐spectra and the sequence lengths of the segments which assume the regular helical conformation in isotactic polymer chains, the IR‐spectra have been measured for isotactic copolymers of normal and deuterated styrenes in various ratios. The absorption intensities of the bands characteristic of the TG skeletal conformation of the isotactic polystyrene molecule have been investigated in relation to the length of the normal styrene sequences in the copolmers. In the case of the highly crystalline samples of the copolymers, the absorption coefficients per normal styrene unit have been found to decrease with decreasing statistical sequence length of the normal styrene units in the copolymer chain. A simple statistical treatment of the intensity data has provided the critical length which is necessary to produce each characteristic band. Each band has its characteristic value of the critical length depending on the vibrational mode to which the band is due. The band intensities measured on the carbon disulfide solution at a low temperature have shown a dependence on the regular sequence length very similar to that of the highly crystalline samples. This indicates that the molecule assumes rather regular helical conformation in solution at a low temperature.