New polymer syntheses XCIII. Hyperbranched homo- and copolyesters derived from gallic acid and β-(4-hydroxyphenyl)-propionic acid

The hyperbranched homopolyester of gallic acid (GA) was prepared by polycondensation of acetylated gallic acid in bulk. Copolyesters of gallic acid and 3-hydroxybenzoic acid (3-HBA) or β-(4-hydroxyphenyl)propionic acid (HPPA) were prepared via the silylated monomers. The degree of branching was varied in both series via the molar fraction of gallic acid. A model reaction with silylated 4-methoxybenzoic acid suggests that all three acetoxy groups of gallic acid can react by ester interchange reactions under the chosen reaction conditions. Furthermore, highly branched copolyesters derived from equimolar ratios of HPPA and 2-, 3-, or 4-hydroxybenzoic acid, vanillic acid, or 4-hydroxycinnamic acid were synthesized. All these copolyesters were found to be amorphous with glass transition temperatures (Tg's) far below that of the hyperbranched poly(gallic acid).