Bioenabled copolyamides from the chemical diversification of muconic acid derivatives

The mass exploitation of petroleum feedstocks over the past century has led to valuable commodities that have changed economies and societies globally, however their usage has incidentally brought about increased pollution and climate change. Currently biobased feedstocks may serve as a replacement feedstock for petroleum that may generate renewable chemicals in key applications, but the array of molecules that can be generated from biology must be expanded. A persisting challenge is how to select the best target molecule from that array of molecules for a specific end use application. One approach involves strategic selection of a biological target that can be used as an intermediate for subsequent chemical conversion to a chemical library. This library can then be screened for its efficacy in the desired end use application. Using this strategy, muconic acid has been identified as an intermediate for synthesizing diacid monomers with new functionalities for property enhancements in Nylon 6,6. The hydrogenation of muconic acid to trans-3-hexenedioic acid (t3HDA) provides an opportunity to screen the effects of grafting single functionalities on a biobased molecule to be used as a property modifier and replacement of adipic acid in Nylon 6,6. In this work the base-catalyzed isomerization of t3HDA to produce trans-2-hexenedioic acid (t2HDA) was studied, and a reaction was engineered to graft nitrogen based aromatic thiols to t2HDA with Michael addition. The grafted monomers were co-polymerized with adipic acid and hexamethylenediamine, and the flame-retardant properties of the synthesized polyamides screened to identify promising nitrogen-containing aromatics to afford improvements in end use performance without compromising on the polyamide's properties. This chemistry was extended to the functionalization of muconic acid and trans-3-hexenedioic acid with a phospha-Michael donor capable of flame-retardant enhancement, diphenyl phosphine oxide. Polymerization conditions were optimized to avoid monomer hydrolysis and obtain consistent molecular weights. Analysis shows the increased value of muconic acid as the difunctionalized monomer preserves polymer crystallinity and viscoelastic properties over monofunctionalized while maintaining similar mechanical performance to virgin nylon 6,6. From these findings it was apparent that hydration and hydrolysis reactions related to inherent water in polycondensation reactions would limit the viability of bio-based nylons. A new strategy would be to harness the functionalities this produces to insert ester linkages in a post-polymerization process. At high temperature a range of carboxylic acids serve as desirable solvents for nylon 6,6 while also serving as reagents for esterification. By leveraging this esterification reaction, the simple carboxylic acids of benzoic acid and dodecanoic acid were used to functionalize bio-based nylon 6,6 containing an alcohol functionality. This process shows promise for compatibility with reactive extrusion processes if conditions can be optimized.