The Role of UV-Vis Spectrometer in Inhibiting Polymerization

Across the world, a considerable amount of the plastics and synthetic fibers used daily are produced from polymerization processes. Thus, there is a significant demand for process optimization and control methodologies compatible with this kind of chemistry.

Although there are various categories into which polymerization reactions can be placed, generally, they all involve an initiation step to activate the polymerization process and the growth of the polymer chain.

This may introduce a chemical species or utilizing high temperatures and/or even light in the case of photoinduced polymerization reactions.1

The polymer chain growth process is known as propagation, and this will continue until termination of the chain is achieved and the reaction comes to an end. This may come about through undesirable side reactions of radical initiators, unwanted auto-polymerization or, more intentionally, by reacting with an inhibitor.

Inhibiting Polymerization

The polymer chain’s length has direct implications on its physical properties and applications.2 managing the length of the chain in a targeted synthesis is typically accomplished via the control and intentional addition of the concentration of inhibitor species.

Executing peak concentrations of inhibitors can be a tricky issue. Too little inhibitor and undesirable reactions can take place, too much inhibitor and it can be a burden to get the monomers to polymerize at all.

This is why for most polymerization reactions, process analytical technologies (PATs) are introduced into the process workflow.

With optimal calibrations, techniques such as Ultraviolet-visible (UV-Vis) absorption spectroscopy can be made use of to track both the spectral profile and concentration of polymer and inhibitor alike, and this output can be incorporated into process control systems.

UV-Vis spectroscopy typically has exceptional sensitivity (below 10-5 molar) for the measurement of various kinds of compounds in the reaction vessel and can be utilized for both qualitative and quantitative measurements.3

It is compatible with a diverse range of compounds and sample types and is a verified PAT for the monitoring of polymerization reactions.

Live Reaction Feedback

A PAT for inhibitor concentration control must have the capacity to conduct rapid online measurements in the reaction vessel. tec5USA, with plenty of expertise in the design and implantation of process spectroscopy, can provide an online UV-Vis Spectrometer with the Polymer extruder sample probe option for this exact purpose.4,5

The spectrometer impresses by offering S/N of ~ 20,000 and is equipped with options to reach a spectral range of 190– 1100 nm. This wavelength range is appropriate for almost all polymerization inhibitors that are most frequently used.

For instance, Cupferron – a common inhibitor – has solid absorption between 210-490 nm, so its concentration can be tracked in this wavelength range.6

A number of longer chain polymer species tend to have absorption moving towards the near infra-red region, so it can be beneficial to monitor a range of spectral regions to extricate the complex reaction mixtures.3

The detection system is made up of a high dynamic range silicon diode array detector consisting of 256 pixels The UV-Vis measurement of the reaction mixture is both reliable and precise due to a wavelength accuracy of 0.2 – 0.3 nm and permanent wavelength calibration.

The detector is also extraordinarily thermally stable, so changes in the environment will not impact the sampling quality.

With the tec5USA UV-Vis Spectrometer, the spectral acquisition time is reduced to a time scale that allows samples of the reaction mixture to be taken as frequently as every few milliseconds.

This means that should undesirable auto-polymerization occur or other rapid reactions, the real-time concentration information can be utilized to modify and optimize the process as required.

Modular Design

The tec5USA UV-Vis Spectrometer is extremely flexible due to its modular design and it offers the possibility of customization to the specific demands of a given reaction.

It has no moving parts making it a maintenance-free device, essential for its role as a PAT and further reducing operating costs and production losses linked with routine downtime for maintenance.

Process control communications options include Modbus, 4.20 mA and OPC, and the spectrometer can be interfaced into a closed-loop control connection to DCS/SCADA systems.

Sampling Options

Polymerization reactions frequently occur under unrelenting conditions, increased temperatures, UV-irradiation and a good number of radical intermediate species formed are extremely reactive.

This means any materials utilized in the fabrication of probes or reaction vessels must especially be chemically inert to prevent contamination and avoid degradation.

tec5USA utilizes the Excalibur HD Extruder Probe to handle hostile sample environments. With the capacity to withstand temperatures up to 300°C, pressure up to 300 bar, with a titanium barrel, and chemically resistant sapphire windows, the Extruder probe is a sturdy sampling probe appropriate for direct insertion in polymer extrusion mixes.

There are a good availability and range of measurement heads, with path lengths of 1 – 10 mm depending on the concentrations and signal intensities expected relative to the chemical species of interest.

The tec5USA UV-Vis Spectrometer is a device that is both extremely flexible and robust relative to online measurements in the demanding environments affiliated with polymerization reactions.

Discover how tec5USA’s instruments and vast expertise in process control spectroscopy can be utilized to improve and optimize your processes.

References

  1. Zivic, N., Bouzrati-Zerelli, M., Kermagoret, A., Dumur, F., Fouassier, J. P., Gigmes, D., & Lalevée, J. (2016). Photocatalysts in Polymerization Reactions. ChemCatChem, 8(9), 1617–1631. https://doi.org/10.1002/cctc.201501389
  2. Roncali, J., Garnier, F., Lemaire, M., & Garreau, R. (1986). Poly mono-, bi- and trithiophene: Effect of oligomer chain length on the polymer properties. Synthetic Metals, 15(4), 323–331. https://doi.org/10.1016/0379-6779(86)90081-0
  3. Su, W.-F. (2013). Principles of Polymer Design and Synthesis, Lecture Notes in Chemistry 82. Principles of Polymer Design and Synthesis (Vol. 82).
  4. tec5. (2021) Products. https://www.tec5.com/en/products, accessed 10th March 2021
  5. tec5. (2021) Multi-Spec UV-vis. https://www.tec5usa.com/multispec-system, accessed 10th March 2021
  6. NIST (2021) Cupferron, https://webbook.nist.gov/cgi/cbook.cgi?Spec=C135206&Index=0&Type=UVVis&Large=on, accessed 10th March 2021 

This information has been sourced, reviewed and adapted from materials provided by tec5USA Inc.

For more information on this source, please visit tec5USA Inc.

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