Synthesis of a novel pH-responding polymer with pendant barbituric acid moieties

A simple method for the synthesis of pH-responding polymers containing barbituric acid moieties is described. The synthesis involves N-methyl-N′-(4-vinylbenzyl) urea (2) preparation and its polymerization in DMF using AIBN as the initiator to give poly(N-methyl-N′-(4-vinylbenzyl)urea) (4) with a number average molecular weight of 4.9×105 as determined by GPC. Cyclocondensation of urea with malonic acid in acetic acid/acetic anhydride affords the polymer (5) with pendant barbituric moieties. The pH-responding behavior of polymer 5 in water indicates that it has excellent pH-sensitivity at pH 6∼7. The potential and the versatility of this work are exciting and include the potential preparation of water-soluble polymers by modification of polyureas, metal chelating materials, and “smart” hydrogels upon crosslinking.