- Author
-
Nyden, M. R.
- Title
- Conformational Structures of Defect-Containing Chains in the Crystalline Regions of Isotactic Polypropylene. BFRL Fire Research Seminar. VHS Video.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
-
Video
November 23, 1999
- Keywords
-
polypropylene
|
structures
- Abstract
- 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 are typically found in metallocene-synthesized polymers. The calculations were carried out as follows. A model of the crystalline region of isotactic polypropylene was constructed from available X-ray data. Ethylene comonomer, regio 2,1-erythro, and stereo-mrrm 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 to determine the extent to which the defect-containing chains are accepted into the crystal and to infer their conformational structures.