Segmental and Chain Dynamics of Isotactic Polypropylene Melts
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- 作者：Georgia Evangelia Logotheti ; Doros N. Theodorou
- 刊名：Macromolecules
- 出版年：2007
- 出版时间：March 20, 2007
- 年：2007
- 卷：40
- 期：6
- 页码：2235 - 2245
- 全文大小：283K
- 年卷期：v.40,no.6(March 20, 2007)
- ISSN：1520-5835
文摘
The properties of isotactic polypropylene (iPP) melts are investigated via atomistic moleculardynamics (MD) simulations in the isothermal-isobaric (NPT) ensemble. A fully flexible model is developed andvalidated by comparing predicted volumetric and thermodynamic behavior with available experimental data.Atomic-level packing in the simulated polymer melt is examined through the calculation of an X-ray diffractionpattern. Segmental dynamics is investigated through the reorientation of the methylene C-H bonds and thedecorrelation function of torsion angles over a wide range of temperatures and pressures. Predicted correlationtimes are in reasonable agreement with experimental values derived from 13C NMR, QENS, and dielectricspectroscopy measurements. The temperature (T) and pressure (P) effects on the relaxation times are comparedby calculating the 
ls/mamobx/40/i06/eqn/ma062234ue10001.gif">/H* ratio, which provides a quantitive measure of the relative importance of P and T on thedynamics. By consistently mapping the atomistic trajectories onto the Rouse model, the dynamical behavior ofthe polymer on the chain level is investigated. Estimates of the segmental friction factor are derived from boththe self-diffusion coefficient and the relaxation times of the first Rouse modes. The zero-shear viscosity is calculatedfrom the friction factor through the Rouse model analysis.