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.