Three water-soluble polymers incorporating increasing levels of 2,3-dihydroxy propyl attached to polyethylenimine (PEI) backbone were synthesized, characterized by NMR, and investigated for their ability to bind boric acid (BA). B-11 NMR spectroscopy showed that BA interacted with the polymeric 2,3-dihydroxy propyls by forming borate monoester and borate diesters in the boron concentration range of 100-1000 ppm and at 0.0775M polymer. Borate monoester species predominated for low functionalization levels (33% of the PEI amines functionalized), whereas borate diester species dominated for the higher functionalized polymers (66-100% of the PEI amines functionalized). All three polymers showed that 100% of the BA was bound as a mixture of borate mono- and diesters at 100-ppm boron. The overall best performer based on total borate ester formation was the 2/3-PEI, with a binding K-d of 631 at 200 ppm boron. Borate ion concentration was measured from the B-11 NMR chemical shift of the BA/borate peak and it decreased as 1/3-PEI > 2/3-PEI > 3/3-PEI. Variable temperature B-11 NMR showed drastic reduction of borate ester species at 65 degrees C. Thus, PEI polymers, as the ones investigated in this work, are reasonable candidates for the selective recovery and recycle of BA. (c) 2006 Wiley Periodicals, Inc.