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1

Solid State ¹³C Nuclear Magnetic Resonance Study of Morphology and Molecular Mobility in Quenched Poly(3-hydroxybutyrate)

100%

Baran A., Vrábel P., Olčák D.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

1144-1146

EN

Single pulse magic angle spinning ¹³C NMR spectra and the carbon spin-lattice relaxation times T₁(¹³C) were used for the study of morphology and molecular mobility in poly(3-hydroxybutyrate) quenched in cold water after melting in a twin-screw extruder. The crystallinity of the quenched sample was found to be comparable with that of virgin material, and the decrease in dimensions of the crystallites grown after quenching was deduced from the single pulse magic angle spinning ¹³C NMR spectra. The spin-lattice relaxation curves for the carbons of the CO, CH, CH₂ and CH₃ groups were found to be bi-exponential, which enables the molecular mobility within crystalline and amorphous domains to be studied. The spin-lattice relaxation times T₁(¹³C) estimated for the carbons of the CO, CH, CH₂ groups show the chain mobility enhancement within crystalline domains of the quenched sample, but the influence of the quenching on the CH₃ group rotation and on the main chain motion within amorphous regions was not observed.

2

Preparation and Characterization of Basic and Er^{3+}-Doped Glasses in the System Y_{2}O_{3}-Al_{2}O_{3}-ZrO_{2}

100%

Klement R., Hruška B., Hronský V., Olčák D.

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vol. 126

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issue 1

302-303

EN

The undoped, and Er-doped yttrium aluminozirconate (AYZ) glasses were prepared by flame synthesis in the form of transparent glass microbeads. The ZrO_{2} content was in the range between 5 and 20 mol. %. The prepared glass microbeads were characterised by optical microscopy, SEM, XRD, DSC, ^{27}Al MAS NMR, UV-VIS-NIR and fluorescence spectroscopy. The thermal stability of AYZ glasses, expressed in terms of the difference between the glass transition temperature, T_{g}, and the onset of crystallization, T_{x}, was not affected by the increasing ZrO_{2} content. The ^{27}Al MAS NMR spectra of studied glass samples reveal that Al atoms are predominantly 4-coordinated in glasses. The AYZ5 and AYZ10 basic glasses were doped with Er^{3+} at the level of 1-5 mol. % of Er_{2}O_{3}. The UV-VIS-NIR/fluorescence spectra show characteristic absorptions/emissions, due to the optically active Er^{3+} ions in the host glasses. The absorption/emission properties of guest ions are not significantly affected by the glass host.

3

Dynamics of ¹H-¹³C Cross Polarization in Nuclear Magnetic Resonance of Poly(3-hydroxybutyrate)

88%

Koval'aková M., Fričová O., Hutníková M., Hronský V., Olčák D.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

1162-1164

EN

Poly(3-hydroxybutyrate) (PHB) is a semicrystalline biodegradable polymer with chains consisting of methyl (CH₃), methylene (CH₂), methine (CH) and carbonyl (CO) groups. The ¹H-¹³C cross polarization NMR measurements were performed on an as-supplied powder PHB sample at a magic-angle spinning rate of 10 kHz. The measured cross polarization build-up curves and their analysis provided information on the dynamics of ¹H-¹³C NMR cross polarization in functional groups with directly bonded hydrogens. The measurements required setting up the Hartmann-Hahn condition, which was inferred from the Hartmann-Hahn matching profiles measured for each functional group. The cross polarization build-up curves displayed an oscillatory course, which indicates the presence of rigid ¹H-¹³C spin pairs isolated from the lattice. The frequency of the observed oscillations is directly proportional to the ¹H-¹³C dipolar coupling constant, which is related to the C-H distance and its value also reflects the mobility of particular functional groups. The values of dipolar coupling constants were derived from splittings in the Fourier transforms of cross polarization build-up curves. The mobility of particular groups was assessed with the order parameter ⟨S⟩ calculated using experimental and rigid lattice values of dipolar coupling constants.

4

Estimation of the Degree of Crystallinity of Partially Crystalline Polypropylenes Using ^{13}C NMR

88%

Hronský V., Koval'aková M., Vrábel P., Uhrínová M., Olčák D.

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vol. 126

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issue 1

409-410

EN

The paper deals with a method for the estimation of the degree of crystallinity for partially-crystalline isotactic-polypropylenes (i-PP) using high-resolution solid-state ^{13}C NMR. For this purpose direct polarization ^{13}C MAS NMR spectra were measured for i-PP samples with different degrees of crystallinity at 98°C. The areas beneath the resonance lines in these spectra correspond to the number of carbons in particular functional groups, while the widths and shapes of the lines reflect the degree of crystallinity, crystalline modifications, distribution of chain conformations and the chain mobility. The ^{13}C MAS NMR spectra, measured using appropriate combination of delay time and high proton decoupling field, made it possible to detect only amorphous domains in the sample. This enabled identification of the lines associated with the amorphous domains in the complete ^{13}C MAS NMR spectra and provided sufficient information for reliable estimation of the degree of crystallinity. The heteronuclear Overhauser enhancement of the ^{13}C NMR signals due to short delay time was taken into account in our calculations.

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1 Hutníková M.

1 Klement R.

1 Uhrínová M.

Solid State ¹³C Nuclear Magnetic Resonance Study of Morphology and Molecular Mobility in Quenched Poly(3-hydroxybutyrate)

Preparation and Characterization of Basic and Er^{3+}-Doped Glasses in the System Y_{2}O_{3}-Al_{2}O_{3}-ZrO_{2}

Dynamics of ¹H-¹³C Cross Polarization in Nuclear Magnetic Resonance of Poly(3-hydroxybutyrate)

Estimation of the Degree of Crystallinity of Partially Crystalline Polypropylenes Using ^{13}C NMR