One-pot solvent-free synthesis and characterisation of hydroxypropylated polyflavonoid compounds

An efficient, one-pot solvent-free synthesis using mild base catalysis has been developed to prepare hydroxyalkylated flavonoid and polyflavonoid compounds. Based on reaction conditions developed with catechin, condensed tannins have been reacted with propylene oxide to give a range of hydroxypropyl substitutions and chain extended compounds. The resulting etherified flavonoid and polyflavonoid products were characterised to reveal the degree of substitutions and non-specificity of hydroxypropylation. Analysis showed the products to have decreased thermal stability with degradation onset between 100 and 200 °C. Hydroxypropylated catechin products have glass transitions (−20 to 80 °C) which decrease with greater substitution, whereas chain-extended hydroxypropylated polyflavonoids show sub-ambient gelation and melt behaviours. An initial application of the hydroxypropylated polyflavonoids was demonstrated by compounding with poly(lactic acid) to produce high tannin content melt-spun fibres. These results demonstrate the facile synthesis of hydroxypropylated flavonoids as a sustainable bio-based feedstock for various material applications.