If you are doing a fractional distillation then firstly i would not worry with the ewashing steps unless the monomer is very impure - i would simply run through a column of basic alumina and then distill. However, even though it has been run through a column (this will remove acidic impurities and other contaminants) i would advise adding inhibitor (DPPH or phenothiazine) to the impure HEA prior to distillation and use a liquid N2 'trap' in the collection vessel (maybe also wrap the condenser in aluminium foil). If you are doing a more simple transfer distillation then pouring liquid N2 on the transfer arm (if you are still allowed to do this these days!!) will prevent spontaneous polymerisation.

Thank you very much for your reply. Indeed we tried almost all those tricks already (using hydroquinone as an inhibitor, maybe your suggested inhibitor would work more effectively). We perform fractional distillation, but we want to be absolutely sure tha we remove any trace of diacrylate, hence the washing steps. But we dried a distillation on the commercial monomer, and still it was a failure... The funny thing is, we never had any problem in the past even when working at slightly lower vacuum, but it became systematic lately....

I do not really understand how pouring liquid nitrogen on teh transfer arme could prevent polymerization, as it occurs exclusively in the distillation flask, and as we are already cooling (ice bath or liq. N2) the collection flasks.

If you can distill the monomer then the sooner it is cooled, especially under high vacuum, the better (hence the liquid N2 on the transfer arm for pure distilled monomer)

i'm guessing the hydroquinone inhibitor is not doing its job. DPPH is an an extremely potent free radical inhibitor - far more so than hydroquinone, that is used routinely during GTP polymerisations for example(this technique is akin to living anionic polymerization and requires extensive distillation of methacrylic monomers). Also, you can tell when it is no longer being effective - DPPH in its native form is purple and gives highly coloured purple solutions - when it is consumed its turns brown. Phenothiazone also undergoes a colour change buts often needs purifying (recrystallizing) before use

Unfortunately, the purification/distillation of monomers such as HEA, HEMA and amino analogues for example is notoriously problematic but also often necessary......good luck!!

It has been a long time since your last advice, but i realized that i never thanked you about it! Indeed, the solution you proposed really changed our lives, as we have never been exposed to such issues as i depicted in my original message since we have started to use it!

So thank you very much... and happy christmas/NY celebrations!!