Ultraslow molecular motions in crystalline polyoxymethylene. A complete elucidation using two-dimensional solid state NMR

Kentgens, A.P.M.; Boer, E. de; Veeman, W. S.

doi:10.1063/1.453730

Cited by 89 publications

(89 citation statements)

References 12 publications

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“…Investigations of POM by 2D exchange NMR without sample rotation confirmed the picture in detail [68]. The geometry and activation energy of the motion has been determined in these experiments [67,68].…”

Section: Helical Jumpsmentioning

confidence: 71%

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Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

1999

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An explanation of the varying (ultra)drawability of semicrystalline polymers is proposed, based on NMR evidence of αc‐relaxation‐associated helical jumps and chain diffusion through the crystallites of polyethylene and several similarly “αc‐mobile” polymers; these include isotactic polypropylene, poly(ethylene oxide), poly(oxymethylene), poly(tetrafluoroethylene), poly(vinyl alcohol), and several others. The chain motions provide a mechanism by which hot drawing of these polymers can extend an initially formed fiber morphology by an order of magnitude to draw ratios > 30, without melting. A second class of polymers, including nylons, poly(ethylene terephthalate), syndiotactic polypropylene, isotactic polystyrene, and isotactic poly(1‐butene) (form I) lack a crystalline α‐relaxation and the associated chain mobility. Therefore, these polymers are “crystal fixed” and drawability is limited to draw ratios < 14, arising mostly from break‐up of crystalline lamellae and deformation of the amorphous regions. On this basis, we can explain which polymers are drawable to high draw ratios, given a sufficiently low level of entanglement. The motion through the crystallites is thermally activated and the applied stress only biases the direction of the jumps; this explains the crucial role of temperature and rate in tensile drawing and solid‐state extrusion processes. The behavior of the crystal‐fixed, poorly drawable polymers strongly suggests that melting, straight chain pull‐out, and sliding on crystal planes are not significantly operative during ultradrawing, and that weak intermolecular forces are not a sufficient condition for ultradeformation. Various stages of drawing are distinguished and other models of ultradrawability are discussed critically.

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Section: Helical Jumpsmentioning

confidence: 71%

“…The first detailed description of large-amplitude reorientations in the crystallites in terms of helical jumps was given by Kentgens et al for POM by 2D magic-angle-spinning exchange 13 C NMR [67]. Investigations of POM by 2D exchange NMR without sample rotation confirmed the picture in detail [68].…”

Section: Helical Jumpsmentioning

confidence: 80%

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

1999

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“…This feature is a consequence of setting "em = n21tlw R and it holds only if the same phase relation is used to construct the g-functions in the evolution and detection period as was assumed in deri ving eq 17. 10 If opposite phase relations are used, i.e., if the echo rather than the anti-echo spectrum is generated, then cross peaks between spinning side bands will appear even in the absence of exchange (see below).…”

Section: Athe Basicrotor Synchronizedmas Two-dimensional Exchange Exmentioning

confidence: 98%

Rotor Synchronized MAS Two‐Dimensional Exchange NMR in Solids. Principles and Applications

Luz

Spieß

Titman

1992

Israel Journal of Chemistry

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Abstract. The principles of the rotor synchronized magic angle spinning (MAS) two-dimensional exchange NMR, first proposed by Veeman and coworkers are reviewed, with particular emphasis on situations where chemical exchange in solids proceeds in concert with molecular reorientation. Calculations of 9'0ss peak intensities as function of the ratio between the chemical shift anisotropy and the spinning rate are presented for several cases. These calculations emphasize the advantage of using slow spinning rates (OlR < OlL~cr) in such experiments when detailed information about mechanistic pathways in solids is sought. Three applications of the method to solid systems using carbon-13 NMR are described. These include: (a) Trimethylsulfoxonium iodide, in which the molecules undergo 120 0-jumps about the molecular C 3 symmetry axis; (b) Tropolone, where the tautomeric hydrogen shift is found to be a consequence of the self diffusion within the crystal lattice. and in general accompanied by molecular reorientation. Here the two-dimensional pattern is used to obtain information about the various mechanisms of the diffusion process; (c) Bullvalene, where a quantitative analysis of the cross peak intensities as function of the mixing time provides kinetic information on two independent processes, viz. symmetric threefold jumps and a concerted Cope rearrangement-molecular reorientation reaction.

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“…[10] corresponds to the signal at the end of the preparation period, while the second line describes its evolution after the mixing period and the PASS sequence. Note that the only differences between Eq.…”

Section: Theorymentioning

confidence: 99%

PATROS—A New MAS Exchange Method Using Sideband Separation: Application to Poly(n-butylmethacrylate)

Reichert

Hempel

Luz

et al. 2000

Journal of Magnetic Resonance

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Ultraslow molecular motions in crystalline polyoxymethylene. A complete elucidation using two-dimensional solid state NMR

Cited by 89 publications

References 12 publications

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

Rotor Synchronized MAS Two‐Dimensional Exchange NMR in Solids. Principles and Applications

PATROS—A New MAS Exchange Method Using Sideband Separation: Application to Poly(n-butylmethacrylate)

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