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

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Baran A., Vrábel P., Olčák D.

Acta Physica Polonica A

2017

vol. 131

issue 4

1144-1146

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.

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

2017

vol. 131

issue 4

1162-1164

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.

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2 Acta Physica Polonica A

2 2017

2 Olčák D.

1 Baran A.

1 Fričová O.

1 Hronský V.

1 Hutníková M.

1 Koval'aková M.

1 Vrábel P.

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

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