MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

被引:17
作者
Chinn, Sarah C. [1 ]
Alviso, Cynthia T. [1 ]
Berman, Elena S. F. [1 ]
Harvey, Christopher A. [1 ]
Maxwell, Robert S. [1 ]
Wilson, Thomas S. [1 ]
Cohenour, Rebecca [2 ]
Saalwaechter, Kay [3 ]
Chasse, Walter [3 ]
机构
[1] Lawrence Livermore Natl Lab, Livermore, CA 94550 USA
[2] Honeywell Inc, Fed Mfg & Technol, Kansas City Plant, Kansas City, MO 64141 USA
[3] Univ Halle Wittenberg, Inst Phys, D-06120 Halle, Germany
关键词
SOLID-PHASE MICROEXTRACTION; NUCLEAR-MAGNETIC-RESONANCE; INDUCED CROSS-LINKING; THERMAL-DEGRADATION; RADIATION-CHEMISTRY; STATE POLYMERIZATION; MOLECULAR ORDER; OLIVE OIL; POLYDIMETHYLSILOXANE; POLYSILOXANES;
D O I
10.1021/jp1013797
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Radiation-induced degradation of polymeric materials occurs through numerous, simultaneous, competing chemical reactions. Although degradation is typically found to be linear in adsorbed dose, some silicone materials exhibit nonlinear dose dependence due to dose-dependent dominant degradation pathways. We have characterized the effects of radiative and thermal degradation on a model filled-PDMS system, Sylgard 184 (commonly used in electronic encapsulation and in biomedical applications), using traditional mechanical testing, NMR spectroscopy, and sample headspace analysis using solid-phase microextraction (SPME) followed by gas chromatography/mass spectrometry (GC/MS). The mechanical data and 114 spin-echo NMR spectra indicated that radiation exposure leads to predominantly cross-linking over the cumulative dose range studied (0-250 kGy) with a rate roughly linear with dose. H-1 multiple-quantum NMR spectroscopy detected a bimodal distribution in the network structure, as expected from the proposed structure of Sylgard 184. The MQ NMR spectra further indicated that the radiation-induced structural changes were not linear in adsorbed dose and that competing chain scission mechanisms made a greater contribution to the overall degradation process in the range of 50-100 kGy (although cross-linking still dominated). The SPME-GC/MS data were analyzed using principal component analysis (PCA), which identified subtle changes in the distributions of degradation products (the cyclic siloxanes and other components of the material) as a function of age that provide insight into the dominant degradation pathways at low and high adsorbed dose.
引用
收藏
页码:9729 / 9736
页数:8
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