Thursday, December 09, 2010

Isosorbide as a BPA replacement

One of the big corn processors from here in the Midwest is suggesting that isosorbide could be used as a replacement for bisphenol A (BPA) monomer in polycarbonates and epoxies and anything else that uses this versatile chemical. While it certainly can be used in place of the monomer-that-has-fallen-into-political-incorrectness, it will not be a drop-in replacement. This can be seen by simple inspection of the chemical structures.

BPA:Isosorbide:There are a couple of key structural differences. First, the overall length between the two hydroxy groups is much larger in BPA than in isosorbide (keeping in mind that the drawings above from Wikipedia are not on the same scale). That means that the comonomers are going to be much closer than in a BPA based system, and will make up a larger volume than before. Second, the stiffness of the central structure is greatly different, in that the phenyl rings in the BPA have some ability to rotate around the central carbon, while the center part of the isosorbide is going to be pretty much as still as a snowboard. Tg will undoubtedly be affected. Also note that isosorbide has more oxygens available for hydrogen bonding, another potential influence on Tg.

Let me be clear on what I am saying: the two monomers will produce different polymers. Not that different is inherently bad. The new polycarbonates produced with isosorbide can and will have very useful properties, but they will be different than those of standard polycarbonate.

If I was looking to replace BPA with another monomer, I'd keep in simple and look at the rest of the bisphenol family. Bisphenol E

and bisphenol F
would be a good starting point to cause the least disruption to existing polymers. You can see that the methyl groups on the central carbon are replaced by one or two hydrogens. The overall length of the molecule remains the same. I'm not sure that enough is known about the exact mechanism of endocrine disruption to dissuade the use of either replacement monomer.


Anonymous said...

Given the biochemical impact of endocrine disruption caused by xenoestrogens, I'd hardly call the current backlash against BPA as simply political incorrectness. That's an ignorant and callous phrasing of the situation. I hope you never experience male infertility or any of the mental or physical side-effects.

In terms of the "how" of endocrine disruption, usually simply looking at the 3D model structure of estrogen and comparing chemicals like BPA and DES make it pretty easy to imagine how the key fits the lock of an estrogen receptor.

Anonymous said...

My immediate thought would be that the benzylic hydrogens in the other bisphenol derivatives would be easily abstractable and therefore produce a less stable polymer.

I'm not sure I agree with the above comment. The amount of BPA that needs to be ingested in order to see any significant detrimental effects on health are considerably larger than the amounts that have been measured to leach out of most of the polymers containing this monomer.

John said...

"...therefore produce a less stable polymer."

PC is already of questionable stability. It needs UV stabilizer to protect against the photo-Fries reaction, so what's a little bit more?

Anonymous said...

I think the second anonymous is sorta right. This is one item out there that has been officially brought to the lime light. What about Bt roundup ready foods no question about that hair chemicals, dyes, cosmetics. Different types of corn additives added to food and soy. As I mentioned there are so many other xeno-estrogens out there this helps, but making some out of a GMO material like corn (91% in USA) is....WOW...i dont get it.

Anonymous said...

Isosorbide is extremely prone to hydroperoxidation, more so than THF due to the ethers present. It will significantly decompose oxidatively to furfural under the conditions of polymerization leading to colored decomposition products. The co-polymers are not stable when exposed to light and become brittle.