Local conformation of glassy polystyrenes with different stereoregularity

The molecular structure of glassy polystyrenes with different stereoregularity was investigated by infrared, Raman, and solid state high resolution ¹³C NMR spectroscopies. The characteristic bands observed in infrared spectrum closely relates to the regular sequence length of conformational arrangement. The out-of-plane mode of phenyl ring in 500-600 cm⁻¹ region, which is one of the most conformational sensitive bands for polystyrene, provided no characteristic peaks concerned with longer regular sequence than four monomers. Raman spectrum showed that most of the bands providing different peaks among polystyrenes with different stereoregularity are assumed local phenyl ring modes. Solid state high resolution ¹³C NMR is available to estimate the gauche content in terms of analysis based on γ-gauche effect. We determined that the gauche content takes 25.0, 27.9, and 34.3% for glassy state of syndiotactic, atactic, and isotactic polystyrenes, respectively. This indicates that the conformational structure of sPS tends to take trans sequence. Since a large content of trans sequence would make the molecular dimension wide, the glassy sPS provided the smallest density for polystyrenes with different stereoregularity.