Dear,
I've made a DOSY on a polymer. The MALDI-TOF, The GPC and 1H NMR spectrum show the presence of a single polymer. However, I've performed a DOSY in order to know the Hydrodynamic Radii of my polymer and I've obtained two different diffusions parameters including two hydrodynamic Radius. I have found we can have some non-covalent bonds perhaps leading to this facts.
Anybody has some explanations ? I would like to understand more about this two different diffusion , what happens in solution ?
Thank a lot.
Thank Roland ! it's very interesting, my solvent was CDCl3 and RT 298K !
You should try lowering the concentration - if there is aggregation you might be picking up single polymers vs polymer aggregates.
What is the polydispersity of the polymer?
Some of the DOSY analysis tools are better than others.....
At 1.18 you would not expect to have multiple populations - sometimes high PDI can show this.
Aggregation in solution can cause multiple diffusion coefficients - varying the concentration will change the proportion of the different aggregates. Changing solvent will also do this.
Dear Bolley,
Do you have different diffusion parameters on different NMR signals of the polymer or do you see/fit (?) a multicomponent model on all NMR signals?
Dear Alfred,
On my DOSY NMR, I can see two different diffusion signals but on my 1H NMR spectrum, MALDI-TOF, GPC I see only one polymer.
Dr. Ross is correct - if you have impurities or solvents in your sample they will have their own diffusion coefficients associated with any NMR signals for those impurities/solvents. If these overlap with the polymer they will be hard to distinguish.
For example, we were looking to study binding of DNA and poly vinylpyridine N-oxide - but the DNA base and the pyridine N-oxide overlapped while the DNA sugar and polymer backbone overlapped so as to be difficult to distinguish... we solved the problem by running the diffusion experiment on DNA only using 31-P - which is not found in the synthetic polymer - the DNA diffusion signal slowed down significantly, inidicating binding. We have done 13-C diffusion as well - for example, with labelled sodium bicarbonate to see if the bicarbonate was associating with an amino acid in solution.
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