Tuesday, November 03, 2015

A Novel Polymer Curing Technique

To update an old expression [*], there is more than one way to cure a polymer. The use of heat and UV-light are quite common; visible light can be used as can e-beams; moisture-/oxygen-curing are options; you could argue that 2-part silicones or urethanes are cured upon mixing (a chemical cure); and there are a few more options that escape me at the moment. Back in August however, researchers announced a new curing technology - this one is based on electricity (Open Access article).

It's one of those "why didn't I think of that" papers, although in my case, as much as I hated electrochemistry, I have an out.

The researchers used 3-[4-(bromomethyl)phenyl]-3-(trifluoromethyl)-diazirine as their crosslinking agent, due to its formation of free radicals in reductive electrochemistry. Once the free-radicals are formed, then we are in a common realm for polymer chemists and my comfort level returns. Take a look at the mechanism:
Electrocuring mechanism
The aryl-carbene can react with any of a number of atoms for crosslinking.

One limitation on this technology is pretty obvious - it is restricted to curing between conductive substrates. (Metals, indium-tin oxide coated surfaces such were used here, inherently-conductive polymers...) But what is far more concerning with this particular curing agent is that it generates N2. Gas generation in a polymer matrix is usually not desirable (unless you are making foams). It's only 1 mole per mole of diazirine, so the total amount is limited since crosslinking agents are seldom used at high levels. But still...

I recognize well that initial discoveries are seldom without issues, so consider this criticism of the nitrogen generation as a setting a direction for the mandatory "future research". But since it will involve electrochemistry, feel free to go ahead without me.

[*] That expression being "There's more than one way to skin a cat". The origins of it aren't entirely clear from what I can find online, but the meaning is: there's more than one way to get a job done. Despite the literal reading of the expression being quite gruesome, it is quite commonly said indicating that no literal intent is intended.

Previous Years

November 3, 2008 - Viscoelasticity Movies


Terry Steele said...

Dear John,

Greetings from a fellow Minnesotan. And thanks for disseminating our research. N2 gas generation may only be a problem depending on how fast you activate the diazirines, matrix solubility, and diffusion rates. Turns out N2 is pretty soluble in a lot of matrices (e.g. Guinness Beer and deep sea divers) and doesn't gas nucleate so quickly--allowing time to diffuse before foaming.

Dont be afraid of the electrochemistry--turns out it's a more elegant method of controlling reduction and oxidation potentials.

Please be on the look out of our forthcoming photo-bioadhesive hydrogels manuscript, fully characterized by real-time dynamic rheometry.



John said...


Good convincing argument on the N2, and I look forward to the new manuscript. Please feel free to alert me to it.