Use of N-substituted-2-pyrrolidone-4-carboxylic acids as bio-based monomers for alkyd syntheses: route to 100% bio-based alkyd emulsions

Bio-based N-substituted-2-pyrrolidone-4-carboxylic acids (PCA) are presented here as an alternative for fossil-based aromatic carboxylic acids in the synthesis of polyesters and alkyds. PCAs are synthesized by reacting itaconic acid with a primary amine, which can be monofunctional or difunctional. The bis-COOH-functional pyrrolidones, prepared from diamines, were studied in model polyester-diols using 2-butyl-2-ethyl-1,3-propanediol (BEPD) as diol and compared with several polyester-diols based on BEPD and aromatic carboxylic anhydride and acids (PA, IPA, and FDCA) and adipic acid. Monocarboxylic acid functional PCAs were studied in alkyd syntheses as alternative for benzoic acid. Coatings based on alkyd emulsions derived from cyclic amine PCAs showed an increased pendulum hardness, whereas linear PCA-nHA-based alkyd emulsion yielded a coating with a lower pendulum hardness. An alkyd emulsion with potentially 100% bio-based content was made using PCA based on aniline (PCA-AN) and succinic acid, which also resulted in a coating with improved pendulum hardness. PCA-AN was also used in the synthesis of an uralkyd (urethane alkyd) and compared with the BA-based reference. The PCA-AN-based coating showed an increased pendulum hardness. Water resistance and dark-induced yellowing of the white pigmented coatings based on PCA-AN-based alkyd emulsions were on the same level when compared to the benzoic acid containing references.