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Shear-Enhanced Crystallization in Isotactic Polypropylene. 3. Evidence for a Kinetic Pathway to Nucleation

Kumaraswamy, Guruswamy and Kornfield, Julia A. and Yeh, Fengji and Hsiao, Benjamin S. (2002) Shear-Enhanced Crystallization in Isotactic Polypropylene. 3. Evidence for a Kinetic Pathway to Nucleation. Macromolecules, 35 (5). pp. 1762-1769. ISSN 0024-9297.

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In situ rheo-optical techniques are combined with synchrotron wide-angle X-ray diffraction (WAXD) to investigate the oriented crystallization precursors that develop upon strongly shearing an isothermal melt of polydisperse isotactic polypropylene (iPP). The “short-term shearing” experimental protocol, developed by Janeschitz-Kriegl and co-workers, is used under conditions previously determined to induce oriented crystallite growth. Surprisingly, the time for these precursors to appear decreases with increasing temperature, tracking the melt dynamics of the polymer moleculesa behavior unanticipated by current models. Thus, nucleation proceeds via a “nonclassical” kinetic pathway that effectively eliminates the activation barrier for nucleation. To characterize the importance of chain length distribution for the formation of nucleation precursors, experiments were performed with model bidisperse systems containing a small percentage of high molecular weight iPP blended with lower molecular weight iPP of matched stereoregularity. Oriented crystallization was not observed for the individual components of the blend under the most extreme experimental conditions investigated, but it was readily observed for the bidisperse blend. This suggests that, under intense shear, nucleation of oriented crystallites is governed by the rheologically determined formation of a critical anisotropic configuration of polymer chains in the melt.

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Kornfield, Julia A.0000-0001-6746-8634
Additional Information:© 2002 American Chemical Society. Received 7 August 2001. Published online 1 February 2002. Published in print 1 February 2002. We are grateful to Dr. A. Prasad (Equistar Chemical) for providing us with the polydisperse polymer used in this study and to Dr. R. L. Sammler (The Dow Chemical Co.) for providing us with the narrow distribution polymers. We thank Dr. Motohiro Seki (Mitsubishi Chemical Co.) for NMR tacticity determination and Dr. Markus Gahleitner (Borealis AG) for measuring the Chisso IR tacticity. Synchrotron experiments were carried out at the beamline X27C of the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the US Department of Energy, Divisions of Material Sciences and Chemical Sciences under Contract Number DE-AC02-98CH10886. We are grateful to Dr. Weidong Liu, P. Wang, and Y. Sun for assistance with synchrotron measurements and to Prof. R. C. Flagan (Caltech) for helpful discussions and for critiquing this manuscript. Financial support from Procter and Gamble, the Cargill-NIST ATP, the Schlinger Fund, and the NSF (DMR9901403) is gratefully acknowledged.
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Department of Energy (DOE)DE-AC02-98CH10886
Procter and GambleUNSPECIFIED
Schlinger Fund, CaltechUNSPECIFIED
National Institute of Standards and Technology (NIST)UNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20170724-112028020
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Official Citation:Shear-Enhanced Crystallization in Isotactic Polypropylene. 3. Evidence for a Kinetic Pathway to Nucleation Guruswamy Kumaraswamy, Julia A. Kornfield, Fengji Yeh, and Benjamin S. Hsiao Macromolecules 2002 35 (5), 1762-1769 DOI: 10.1021/ma0114180
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79298
Deposited By: Ruth Sustaita
Deposited On:24 Jul 2017 18:36
Last Modified:03 Oct 2019 18:18

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