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Rapid Stretching Vibration at the Polymer Chain End.

Stretching vibrations of aliphatic C-D bonds at the chain end and midchain site of partially deuterated polystyrene (PS) were determined by Fourier transform infrared (FT-IR) spectroscopy. It was first found that the stretching vibration at the chain end is more rapid compared to that at the midchain site in the glassy bulk state. The difference in the frequencies of the stretching vibrations at the chain end and midchain site changed little even when the PS was dissolved in toluene. Moreover, the DFT vibrational frequency calculations showed that the C-D bonds at the end site intrinsically have higher vibrational frequency because of lower intramolecular interactions at the chain end. From these results, it was concluded that the main origin for the local rapid stretching vibration at the chain end is not intermolecular effects but reduced intramolecular interactions induced by the discontinuity of the repeating unit at the chain end.