Synthesis of Novel Renewable Polyesters and Polyamides with Olefin Metathesis

Unsaturated and hydroxyl-functionalized C6-dicarboxylic acids were successfully synthesized via olefin metathesis from methyl vinyl glycolate (MVG), a renewable α-hydroxy C4-ester product from Lewis-acid carbohydrate conversion. Addition of a second-generation Hoveyda–Grubbs catalyst to neat MVG leads to a near quantitative yield of dimethyl-2,5-dihydroxy-3-hexene­dioate (DMDHHD). Additional hydrolysis and hydrogenation steps form interesting polymer building blocks like 2,5-dihydroxy-3-hexenedioic acid (DHHDA) and 2,5-dihydroxy­adipic acid (DHAA). Their use in polyester and polyamide synthesis is demonstrated after determination of their physical and spectroscopic characteristics. Copolymerization of DHHDA with l-lactic acid for instance produces a cross-linked poly­(l-lactic acid-co-DHHDA) polyester. Proof of cross-links is ascertained by NMR and FTIR. Substantial impact on the melting, thermal, and polar properties of PLA are observed already at low amounts of DHHDA (0.1 mol %) in accord with the presence of cross-links in the polymer. Biobased polyamides were also synthesized by equimolar reaction of DHHDA with hexamethylenediamine, producing a renewable polyamide analogue of the petroleum-based nylon-6,6. Interestingly, the as-synthesized polyamide (α-bishydroxylated unsaturated polyamide, HUPA) possesses similar thermal stability as nylon-6,6 but shows different chemical properties as a result of the double bond and α-hydroxy functionality.