Date of Award
Doctor of Philosophy
Jason S. Chen
Michael R. Kessler
As petroleum feedstocks start to dwindle, it is becoming more important to find acceptable replacements for materials made from these feedstocks. Polyurethanes have classically been synthesized from petroleum-based feedstocks, and depending on its properties, polyurethanes can be used in everything from foams, to construction plastics. In recent years there has been an increasing amount of research trying to replace petroleum-based chemicals those derived from biobased sources. One such compound, isosorbide, is a rigid diol that has seen an increasing amount of research as a replacement for hard segments of polymers. While there has been much work incorporating isosorbide into polyurethanes as a diol, there has been relatively little work incorporating isosorbide as a diisocyanate. Previously, isosorbide has been directly functionalized via and SN2 and oxidation-reduction method. Our approach introduced a tether, succinic anhydride, which is increasingly produced through fermentation. Reaction of isosorbide with succinic anhydride results in a dicarboxylic acid that can be subsequently converted to a diacid chloride. The diacid chloride then undergoes a two-step Curtius Rearrangement to afford an isosorbide-based diisocyanate. Subsequent proof of concept polyurethanes were synthesized and characterized to analyze the properties of our newly synthesized diisocyanate.
Tackifiers are a relatively unknown class of molecules that are used extensively in the adhesives industry. Usually derivatives of resin acids (diterpenes), terpenes, or petroleum-based starting materials, tackifiers, are used to improve wetting, tack and adjust the glass transition temperature of an adhesive. While most small molecules are crystalline and have a very distinctive transition from a solid to a liquid, tackifiers are glassy amorphous small molecules that have a glass transition, like a polymer. Tackifiers are usually blend with block copolymers to form pressure sensitive adhesives, i.e. tape.
It was during the synthesis of our biorenewable diisocyanate that we discovered a molecule which possessed interesting properties. The succinate diacid derivative of isosorbide was extremely viscous and therefore difficult to transfer to the next reaction. It also made everything it touched extremely sticky. With this interesting result, several analogs were synthesized to gain some insights into this emergent property. Increasing the tether length attached to isosorbide by one methylene group had no effect on how tacky the material was, but shifted the temperature at which it was most tacky down by approximately 30 ÃÂ°C. Conversely, introducing rigidity into the tether, increased the temperature of max tack by 30 ÃÂ°C. We believed the carboxylic acids of the tethers were contributing to this emergent property of tack, therefore methyl ester derivatives were synthesized and tested. While the max tack temperature shifted, there was little to no effect on maximum tack of these molecules. Further derivatives are being investigated to hopefully gain insights into the structural aspects of these molecules that are leading to tack.
The extra functionality (internal alkene) of our maleate-based tackifier led us to investigate the ability to make "smart" tackifiers, by either permanently or reversibility converting our tackifier using an external stimuli, such as heat or UV-light. Two proof of concept polymers were synthesized, one from a maleate diacid-based monomer and the other from a maleate methyl ester-based monomer. Interestingly, we discovered these monomers polymerize at significantly different temperatures and result in varying morphology. This led us to investigate the polymerization of our diacid-based polymerization. It was discovered, using 1H NMR, FTIR, and GPC studies, that our diacid-based tackifier was polymerizing through a condensation mechanism rather than through a radial mechanism.
Michael Dennis Zenner
Zenner, Michael Dennis, "Biorenewable materials from isosorbide" (2015). Graduate Theses and Dissertations. 16095.