Synthesis and characterization of renewable polyesters based on vanillic acid

Vanillic acid, potentially derived from biosourced feedstocks, was used as starting material in the synthesis of novel polyesters. A diester obtained by esterification and etherification of vanillic acid served as first monomer, in combination with resorcinol bis(2-hydroxyethyl) ether, hydroquinone bis(2-hydroxyethyl) ether, or aliphatic diols with different carbon chain lengths as second monomers, and antimony trioxide as catalyst to synthesize a series of polyesters by melt polymerization. The materials obtained had polystyrene-equivalentM(n)= 10,000-19,500 g/mol andM(w)= 19,300-39,500 g/mol. Thermal analysis yielded melting temperatures of 76-114 degrees C and onset decomposition temperaturesT(5%)= 321-360 degrees C. Dynamic mechanical and tensile testing confirmed that polyesters derived from vanillic acid have properties superior to poly(ethylene terephthalate) (PET). Aqueous degradation experiments with bulk polyester samples at different pH over 16 weeks led to intrinsic viscosity decreases of 9-23% under neutral conditions (pH 7), 10-26% under acidic conditions (pH 3), and 7-19% under alkaline conditions (pH 12). The results obtained show that the good thermal stability and degradability of vanillic acid-based polyesters, and the tunability of the properties of these materials through selection of the diol monomer used in their synthesis, make them excellent biosourced replacements for commercial polyesters such as PET.