Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering
S Arrese-Igor1, A Arbe, A Alegría
1Departamento de Física de Materiales UPV/EHU, Apartado 1072, 20080 San Sebastián, Spain.
The Journal of Chemical Physics
|July 23, 2004
Summary
We studied phenylene ring dynamics in glassy polysulfone using neutron scattering. Our findings reveal temperature-dependent oscillations and pi-flips, crucial for understanding thermoplastic mechanical properties.
Area of Science:
- Materials Science
- Polymer Physics
- Neutron Scattering
Background:
- Molecular motions in polymers significantly influence mechanical properties of engineering thermoplastics.
- Glassy polysulfones, like bisphenol-A-polysulfone, are widely used but their molecular dynamics require detailed investigation.
- Selective deuteration allows isolation of specific molecular group dynamics for clearer analysis.
Purpose of the Study:
- To investigate the dynamics of phenylene rings in glassy bisphenol-A-polysulfone.
- To correlate observed molecular motions with the material's mechanical properties.
- To develop a comprehensive model for phenylene ring dynamics across a wide time scale.
Main Methods:
- Quasielastic neutron scattering (QENS) using time-of-flight and backscattering spectrometers.
- Selective deuteration of methyl groups to enhance incoherent scattering from phenylene rings.
- Neutron diffraction with polarization analysis for structural characterization.
Main Results:
- Identified fast oscillations with increasing amplitude and pi-flips as key phenylene ring motions.
- Observed a broad distribution of relaxation times due to the amorphous state's structural disorder.
- Covered a dynamic range from 10^-13 s to 10^-9 s.
Conclusions:
- A new model combining oscillations and pi-flips accurately describes phenylene ring dynamics.
- The proposed model successfully explains neutron scattering data across the investigated dynamic range.
- Understanding these dynamics is vital for tailoring the mechanical performance of polysulfones.
More Related Videos
Related Concept Videos
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:37NMR Spectroscopy of Benzene Derivatives
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling constants depend...
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
01:08Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
01:27¹H NMR: Long-Range Coupling
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.