Synthesis of a diallylammonio propanephosphonate-alt-(sulfur dioxide) copolymer and its evaluation as an antiscalant in desalination plants

The cationic monomer N,N-diallyl-3-(diethylphosphonato)propylammonium chloride was cyclo-copolymerized with sulfur dioxide in dimethylsulfoxide using azoisobutyronitrile as initiator to afford a cationic polyelectrolyte (CPE) having a (diethylphosphonato)propyl pendent moiety. The CPE on acidic hydrolysis of the diester groups gave pH-responsive polyzwitterionic acid (PZA) which on treatment with one and two equivalents of NaOH gave zwitterionic/anionic polyelectrolyte (ZAPE) and dianionic polyelectrolyte (DAPE), respectively. The solution properties of CPE, PZA, ZAPE and DAPE were investigated in detail using a viscometric technique. For comparison, the solution properties of the polymers were correlated with those of the structurally similar polyzwitterion prepared from copolymerization of the corresponding zwitterionic monomer ethyl-3-(N,N-diallylammonio)propanephosphonate and sulfur dioxide. Evaluation of antiscaling properties using concentrated brine solutions revealed that DAPE at a meagre concentration of 10 ppm is very effective in inhibiting the formation of calcium sulfate scale, and as such can be used effectively as an antiscalant in reverse osmosis plants.