Synthesis of Carboxylic Acid and Ester Mid-Functionalized Polymers using RAFT Polymerization and ATRP

Abstract

Polymers with a single central point of carboxylic acid functionality were prepared by living radical polymerization methods, RAFT and ATRP. A convenient water-based synthesis of a Y-branched ATRP initiator from 3,5-dihydroxybenzoic acid and 2-bromopropionyl bromide, from which the Y-branched RAFT agent is then subsequently derived, is described. Polymerization occurred uniformly from both of the RAFT groups to give chains of equal length as shown by hydrolysis. ATRP polymerization based on an ester derivative of 3,5-bis(2-bromopropionyloxy)benzoic acid as initiator was well controlled, whereas the free carboxylic acid gave inconsistent performance. The ability to couple functional molecules to the middle of polymers would provide better protection or interaction of the functional molecule with the polymer than conventional end attachment. This would find applications such as in drug delivery where more efficient protection would allow the use of lower molecular weight polymers.