Proton NMR Characterization of Room-Temperature Aging After Modest Thermal Cycling in Isotactic Polypropylenes

Published

July 1, 2003

Author(s)

David L. VanderHart, Chad R. Snyder

Abstract

An proton NMR method, based on simple Bloch-decay spectra in the solid state, is presented that enables one to follow, with excellent sensitivity, structural changes associated with aging in semicrystalline polymers whose Tg is well below the aging temperature. The method is demonstrated for 2 representative isotactic polypropylene (iPP) samples, a Ziegler-Natta and a metallocene product. Starting with samples that had been melt crystallized at a cooling rate of 1 C/min and then aged at ambient temperature for long periods of time, subsequent mild heating cycles between ambient temperature and temperatures below 90 C were applied. Such heating cycles remained more than 70 C below the major crystalline melting temperature for iPP. Aging at 20 C was monitored by NMR over aging times, 10 min 150 ms) value of T1xz, the relaxation along the quantization axis of the toggling frame in a multiple pulse (MP) experiment.

Citation

Macromolecules

Volume

36

Issue

No. 13

Pub Type

Journals

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Keywords

aging, isotactic polypropylene, morphology, NMR, proton, reversible, secondary crystallization

Citation

VanderHart, D. and Snyder, C. (2003), Proton NMR Characterization of Room-Temperature Aging After Modest Thermal Cycling in Isotactic Polypropylenes, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852059 (Accessed April 19, 2024)