Entanglement and network formation in polystyrene: Viscoelastic behaviour from pulsed NMR
✍ Scribed by A. Charlesby; E.M. Jaroszkiewicz
- Book ID
- 103071459
- Publisher
- Elsevier Science
- Year
- 1985
- Tongue
- English
- Weight
- 815 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0014-3057
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✦ Synopsis
A series of NMR proton spin-spin relaxation measurements in three monodispersc polystyrene samples over a range of temperatures shows the conditions required for the existence of a dynamic network in polystyrene due to entanglements. The density of entangled units, N,,, i.e. their number per unit mass, can be determined by this NMR technique and is found to decrease with increasing temperature, in a manner which indicates its dependence on free volume, as in viscosity. The 7"2~ relaxation time for low molecular weight,polystyrene and T2s for high molecular weight polystyrene increase with increasing temperature approximately as does (viscosity) ~,.5. The NMR data provide a quantitative value for the elastic modulus, and its dependence on temperature, both being in agreement with the experimental data previously obtained from viscoelasticity. The model can be extended to analyse creep and subsequent recovery. The transition in viscosity from a M ~ to a M ~4 can also be deduced from the NMR results.