Time-Domain Nuclear Magnetic Resonance (TD-NMR) for Analysing Polymers

The plastic business of this large specialty chemical company deliver a wide range of technology-based solutions and products to customers in roughly 160 countries and in high-growth sectors such as water, electronics, energy and agriculture.

The company operates an analytical laboratory for studying the different properties of polymers. The laboratory requires to run an average of 200 samples each week. This is done with a liquid chromatographic method which both generates huge quantities of waste solvent, and needs the complete attention and time of a single technical operator.

The polymer analyses, which originally demanded a full week’s time from one dedicated technical personnel using the existing method, is now being performed by a Bruker minispec TD-NMR analyzer in just 1-2 hours, and in an unsupervised manner. It is now being used every single day, with no interruption and without the need for solvents.

Senior Research Engineer

The Objectives

The company tried to find a better method in order to fulfil the following objectives:

  • Reduce operational time requirements
  • Reduce costs
  • Improve accuracy of measurements

Reasons for Choosing the Minispec

The company chose the Minispec for the following reasons:

  • Rapid measurement
  • No sample preparation
  • Unsupervised measurements
  • Small instrument footprint
  • No solvents required
  • Accurate and precise quantitative prediction
  • Easy to use

Polymer Development

A polymer can be defined as a macromolecule or large molecule having a number of subunits. Both natural and synthetic polymers, due to their extensive range of properties, play a ubiquitous and important role in daily life.

Polymers span from known synthetic plastics like polystyrene to natural biopolymers like proteins and DNA basic to biological function and structure. Both synthetic and natural polymers are created by polymerization of several small molecules called monomers.

Their large molecular mass with regards to small molecule compounds produces unique physical properties, which includes viscoeleasticity, toughness, and a tendency to form glasses and semicrystalline structures instead of crystals.

Development of improved processes or polymers involves very close monitoring of the amount of polymerization as a function of the different parameters involved in manufacturing. In order to optimize these parameters, several polymer samples require to be studied for quantitative estimation of the amount of polymerization attained under specific conditions.

Even after this process is developed and scaled up, continuous monitoring of the final product is needed for product quality control. This involves analysing several polymer samples each day with high accuracy and precision.

Time-Domain Nuclear Magnetic Resonance (TD-NMR)

TD-NMR is a highly powerful technique, which can be implemented easily, thanks to the benchtop NMR instrument of Bruker, the Minispec. It is an alternative to typical NMR, commonly used in structural analysis. In TD-NMR, it is possible to use permanent magnets as it works at low magnetic fields. Permanent magnets are simple, inexpensive and do not need extensive cooling by liquid gases. However, the low magnetic field results in a low resolution. This is inadequate for obtaining Fourier-transformation frequency spectra. Hence TD-NMR receives the data from the analysis of dependence of signal intensity on time. The signal time-dependency is either fitted directly with appropriate equations or relaxation time constants are obtained from it.

The Minispec records key data from all target atomic nuclei in the sample non-invasively. The signals are mathematically studied in a time domain using automated software with the final prediction on the screen. It is possible to automate the measurement process and operate the instrument by non-NMR experts.

Precise results with TD-NMR

Figure 1. Precise results with TD-NMR

Existing Company Method

The company operates an analytical laboratory for analyzing different polymer properties. One of these is % xylene soluble measurement, which is a quantitative indicator of the amount of polymerization. The Laboratory runs an average of 200 samples every week. These analyses were done previously with a liquid chromatographic method, which generated considerable quantities of waste solvent and needed the services of a full time technical operator.

The company required a means to bring down the operational cost and improve measurement precision.

The Proposed Solution

Using a robotic automation accessory, Bruker’s desktop TD-NMR was installed on the lab bench. The user was offered brief training needed to use the instrument.

The TD-NMR applications or research group of Bruker worked closely with the senior research engineer and operators to design calibrations and custom applications to suit each specific need. This instrument is being used every day, but the multiple analyses that previously required one week of a technical operator’s time, is now conducted automatically and in only one to two hours. The results database are then being updated directly.

There is no other preparation required for this new measurement other than dropping the samples into tubes and arranging them in the autosampler rack. As the new measurement is non-invasive the same sample can be used for other analyses if needed.

Conclusion

Using Bruker’s desktop TD-NMR, the company has improved its polymer analyses efficiency. The result is considerable savings in both cost and time and also the added benefit of improved precision.

This information has been sourced, reviewed and adapted from materials provided by Bruker BioSpin - NMR, EPR and Imaging.

For more information on this source, please visit Bruker BioSpin - NMR, EPR and Imaging.

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