solvent mediated crystallisation

Hi,
on preparing a partially ionic polymer with PEG side-chains I have
obtained what appears to be an amorphous polymer with a rather low glass
transition temperature. This is seen from its ability to form homogenous
films and its appearance in general. I have not yet made thermal
measurements, DSC is currently down.
On redissolving, a large part goes into solution but some of it forms a
rather insoluble precipitate. This melts on heating to give the same
amorphous behaviour as before.
My theory is that on adding solvent, crystallisation is somehow promoted
by adding solvent and the crystalline parts are hardly soluble. I am not
sure whether this is a likely explanation, though and welcome any
comments...
Regards,
Jeppe
Reply to
Jeppe Madsen
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What are the ions in the "partially ionic polymer" and what is the solvent? If the ion are carboxylate salts, what are the cations, metal ions, quaternary ammonium compounds,? Are ions aggregating in solution?
Since PEG is soluble in most solvents (toluene to water) I do not think that the PEG side chains are likely to crystallize? On the other hand, there are reports in the literature of strong interactions between PEG and polyacrylic acid (no, I do not have any references).
Transparency usually does mean that the polymer is amorphous, but it is not a guarantee of lack of crytallinity. Highly nucleated PP is transparent, because the crystallite size is so small.
Regards,
Ernie
Reply to
Ernie
What happens to transparency and to solubility (i.e to crystallinity) after you hold your polymer just below Tg for some time?
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Reply to
Rolf Wissmann
Well, the anions attached to the backbone are highly conjugated organic and the cations lithium. The behaviour is seen in several polar solvents I tried, methanol, acetonitrile etc. The acrylic acid content is very small(though likely present). Actually, the polymer is not transparent due to chromophoric anions. This makes it pitch black.
The PEG-chains are rather short and these are known to be able to crystallise. This normally takes very pure samples, though. Possible the vicinity imposed by the attachment to the polymer bb makes a new situation...
Thanks for your comments as well as Rolf's. I'll have to find a way to make the DSC and go on from there.
regards, Jeppe
Reply to
Jeppe Madsen
I can't give you any help for your specific problem, but I have encountered similar problems with a different kind of polymer. In my case the polar solvent dissolved the polymer (I assume an ionized state in solution), but after precipitation and drying the polymer could not be re-dissolved. I don't have any hard data, but I think this may be due to some sort of ionic crosslinking or polyelectrolyte complex.
I don't know about short PEG-chains, but for longer ones you don't need very pure samples (stuff from normal lab-scale synthesis will do). The side-chain crystallization can easily be detected by DSC. But I doubt the crystalization will persist in a polar solvent.
Regards, Oliver
Reply to
Oliver 'Ojo' Bedford

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