The radicals that drive the reaction
Polymerisations and oxidations run through radicals: initiators make them, chains carry them, and inhibitors catch them. EPR (electron paramagnetic resonance) sees the radicals themselves. It shows when a reaction starts, how fast it runs, and when an inhibitor has been used up, which is often the moment a monomer starts to polymerise by itself.
Where it is used
- Radical polymerisation of monomers such as styrene and acrylics
- Inhibitors, such as stable nitroxide radicals, in monomers during distillation and storage
- Initiator systems and their decomposition
- Oxidation of hydrocarbons and other organic materials
- Photochemical reactions, with the sample irradiated in the instrument
Typical tasks are checking how much inhibitor is left in a monomer, comparing initiators and inhibitors, following a reaction in time, and finding out why a reaction behaves differently from batch to batch.
Stable radicals directly, short-lived ones with a trap
A stable radical such as a nitroxide inhibitor gives a spectrum whose size is its concentration, so its consumption can be followed directly. Radicals that live only for a moment are caught with a spin trap, which makes a stable compound that can be measured. The pattern of the spectrum tells what kind of radical was trapped.
What it adds
- Sees radicals directly and selectively, in the presence of everything else in the sample
- Quantitative, with a reference sample
- Follows fast and slow changes in time
- A warning level for an inhibitor can be set long before a problem occurs
- Benchtop instruments make it practical in a process or development laboratory
Points that matter in practice
- The consumption of an inhibitor depends on temperature, oxygen and impurities, so measure under conditions that represent your process, and set the alarm level from your own experience
- Oxygen broadens the lines of many radicals, so handle the samples in a consistent way
- Choose the spin trap to suit the radicals and the medium, and compare results only within the same method
- Monomers need safe handling, and samples may have to be taken under inert conditions
- The link between the radical level and the behaviour of the process has to be established for your own system
From your reaction to a routine method
Describe your system and your question. MSY Consulting runs feasibility measurements, helps you choose the reference and the conditions, and trains your team until the method is part of your routine.
Let's talk about your application
Send an email describing your instrument and your application, and you will get a reply.
contact@msyconsulting.euMSY CONSULTING SAS · Wissembourg, France · LinkedIn