Molecular Dynamics Simulations Combined with Large Angle X-ray Scattering Technique for the Determination of the Structure, Conformation, and Conformational Dynamics of Polyphosphazenes in Amorphous P
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- 作者：Ruggero Caminiti ; Mario Gleria ; Kenny B. Lipkowitz ; Giuseppe M. Lombardo ; and Giuseppe C. Pappalardo
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：March 5, 1997
- 年：1997
- 卷：119
- 期：9
- 页码：2196 - 2204
- 全文大小：245K
- 年卷期：v.119,no.9(March 5, 1997)
- ISSN：1520-5126
文摘
Suitable parameter sets for the CHARMm force field were derivedusing the Dinur-Hagler energy second-derivative procedure, on the basis of SCF calculations at the 6-31G*level, for the uncommon structural units inpoly(phenoxyphosphazenes) [P=N, P-N, P-X (X = aryloxy)].It is shown that application of molecular dynamics(MD) simulations, in combination with experimental energy dispersiveX-ray diffraction (EDXD) measurements,provide unambiguous structural and conformational information onamorphous polymers. The procedure for theanalysis of the EDXD data involves comparison of computed atom-atomradial distribution function (RDF) curvefrom MD simulations for the various polymer backbone conformations,with the RDF obtained from experimentalX-ray scattering data. The applicability of this combinedexperimental/computational methodology is illustrated onthe amorphous poly[di(4-methylphenoxy)phosphazene](PMPP). The results showed that (i) the backboneconformation is safely [TC]n rather than[T3C]n and (ii) the computed RDFsare best assessed by using a MD simulationtechnique that avoids assumption of static chain conformation and theneeded best fit of the distance dependentparameters sjk. In this methodof analysis, the RDF that to be compared with the experimental one isdirectly calculatedfrom all microstates collected during the entire simulation period.Validation of the polymer model provides acomplete picture, otherwise experimentally inaccessible, of theinternal fluctuations of the polymeric chains. Thecomputational protocol delineated for analysis of EDXD data is generaland its application specifically necessarywhen highly flexible amorphous polymers are involved.