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View Journal Article: The Conformational Structures of Defect-Containing Chains in the Crystalline Regions of Isotactic Polypropylene Citation: Nyden, M. R., Vanderhart, D. L. and Alamo, R. G. (2001). The Conformational Structures of Defect-Containing Chains in the Crystalline Regions of Isotactic Polypropylene. Computational and Theoretical Polymer Science 11 (3). 175-189. Collection: Polymer Publications     Attached Files Name Description MIMEType Size Downloads vanderhart0301.pdf   vanderhart0301.pdf application/pdf 596.57KB 0 Title The Conformational Structures of Defect-Containing Chains in the Crystalline Regions of Isotactic Polypropylene Author(s) Nyden, M. R. Vanderhart, D. L. Alamo, R. G. Keyword(s) C13 NMR solid state defects partitioning assignments simulated annealing quantum mechanical calculations Abstract/Summary Calculations were performed to assign defect-resonance patterns observed in solid state 13C NMR spectra obtained from the crystalline regions of isotactic polypropylene. The spectral features of interest are associated with stereo, regio, and comonomer-type defects which can typically be found in metallocene-synthesized polymers. The calculations were carried out as follows: A model of the crystalline region of defect-free isotactic polypropylene was constructed from available X-ray data corresponding to the a-lattice. A series of irregularities including ethylene comonomer, stereo-mrrm, regio 2,1-erythro, and butylene comonomer defects were introduced one at a time at various positions in a specific stem occupying a central position in the model crystallite. Low-lying conformations were then obtained from simulated annealing calculations that were initiated from these structures. Finally, quantum mechanical calculations were performed on representative segments of the defect-containing chains excised from the annealed crystallites and the calculated chemical shifts were compared to the observed resonances. The results of the calculations were used as a basis for interpreting the NMR intensities of defect-related resonances in terms of the partitioning of defects and to help establish the conformational structures of the defect-containing stems. Publisher Elsevier Science Date 2001-01-01 Copyright Notice Array Journal Computational and Theoretical Polymer Science Volume 11 Pages 175-189 Issue 3 Copyright Agreement on Additional Notes Computational and Theoretical Polymer Science 2001; 11(3): 175-189; Sponsorship: R.G. Alamo acknowledges support from NSF grant # DMR9753258.   User Comments   Created: Wed, 01 Nov 2006, 20:51:53 EST Detailed History

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