High-temperature pulsed-field-gradient multidimensional NMR of polymers

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Pulsed-field-gradient (PFG) techniques are crucial for detecting 2D/3D NMR cross peaks in synthetic polymers.
• Limited polymer mobility causes rapid T2 relaxation, hindering experiments like HMBC that rely on coherence transfer via J couplings.
• High-temperature NMR enhances molecular motion and line narrowing, but has previously precluded PFG method application.

Purpose of the Study:

• To introduce a novel NMR probe for high-temperature pulsed-field-gradient (PFG) coherence selection experiments.
• To demonstrate the capability of this probe for analyzing polymer structures at elevated temperatures.

Main Methods:

• Development and utilization of a new NMR probe designed for high-temperature operation.
• Application of PFG coherence selection experiments at temperatures relevant to polymer analysis (e.g., 120°C).
• Acquisition of PFG-HMBC spectra for a specific ethylene/1-hexene/1-butene copolymer.

Main Results:

• The new probe successfully performs high-temperature PFG coherence selection experiments.
• PFG-HMBC spectra were obtained for a copolymer at 120°C, demonstrating the probe's efficacy.
• The study overcomes the previous limitation of high temperatures precluding PFG methods in polymer NMR.

Conclusions:

• The developed high-temperature PFG NMR probe expands the applicability of advanced NMR techniques to polymer analysis.
• This innovation facilitates the study of minor structural components in polymers that were previously inaccessible.
• The method is validated for analyzing copolymers at industrially relevant temperatures.