1. Trans content in atactic polystyrene estimated by double-quantum solid-state NMR.
- Author
-
Dunbar MG, Novak BM, and Schmidt-Rohr K
- Subjects
- Anisotropy, Molecular Conformation, Probability, Quantum Theory, Rotation, Stereoisomerism, Torsion Abnormality, Magnetic Resonance Spectroscopy methods, Polystyrenes
- Abstract
The conformational statistics of atactic polystyrene have been investigated by solid-state NMR, on a sample labeled with 25% 13CH2 groups. Double-quantum pulse sequences are used to select statistically formed 13C-13C spin pairs. An experiment correlating the 13C-13C internuclear vector with the 13C chemical-shift anisotropy determines the conformational statistics of a single backbone torsion angle. Double-quantum experiments correlating the 13CH2 chemical-shift anisotropies of two adjacent segments provide information on two consecutive torsion angles. The analysis of the spectra yields a trans content of 68% (+/-10%). This represents the first direct experimental estimate of the trans/gauche ratio in atactic polystyrene. The trans content found here agrees well with rotational-isomeric-state models but is inconsistent with results from more elaborate atomistic models that take packing effects into account.
- Published
- 1998
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