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1

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

100%

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.

2

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

100%

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.

3

Solid State ^{13}C NMR Study of Modified Polyhydroxybutyrate

86%

Vrábel P., Hronský V., Fričová O., Koval'aková M., Chodák I., Alexy P.

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vol. 126

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issue 1

419-420

EN

Structural changes in polyhydroxybutyrate (PHB) brought about by addition of chain extender and/or plasticizer were studied using ^{13}C MAS NMR spectra, which were measured using the direct polarization technique at 30 and 98°C. Four resonances associated with the CO, CH, CH_{2} and CH_{3} groups of PHB were observed in the spectra. The CH_{3} resonance appearing at 98°C shows splitting into two lines related to the crystalline and amorphous regions. Analysis of the CH_{3} resonances made it possible to estimate the influence of applied modifications on crystallinity and distribution of conformations in amorphous and crystalline domains of PHB samples.

Refine search results

3 Acta Physica Polonica A

1 2017

2 2014

3 Hronský V.

3 Koval'aková M.

2 Fričová O.

2 Olčák D.

2 Vrábel P.

1 Alexy P.

1 Chodák I.

1 Hutníková M.

1 Uhrínová M.

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

Solid State ^{13}C NMR Study of Modified Polyhydroxybutyrate