Thiol-promoted catalytic synthesis of diphenolic acid with sulfonated hyperbranched poly(arylene oxindole)s.

Acid-catalyzed condensation of levulinic acid and phenol into high yields of diphenolic acid (>50%) is possible with a combination of sulfonated hyperbranched polymers and thiol promotors, either added as a physical mixture or bound to the polymer by ion-pairing.