Synthesis and application of polyzwitterionic and polyampholytic maleic acid-alt-(diallylamino)propylphosphonates

Ammonium persulfate-initiated alternate copolymerization of maleic acid with phosphonic acid monomer [(CH2CH–CH2)2NH+(CH2)3PO3H2Cl−] (I) and phosphonate ester monomer [(CH2CH–CH2)2NH+(CH2)3PO3Et2Cl−] (II) gave polyzwitterion (PZ): poly[(I–HCl)-alt-maleic acid] III and polyampholyte (PA): poly[(II)-alt-maleic acid] IV, respectively. PA IV, upon ester hydrolysis, gave PZ III. The pH-induced changes of backbone charges in tetraprotic III (with respect to each repeating unit) and diprotic IV were examined by viscosity measurements. PA IV exhibited antipolyelectrolyte character in the presence of neutral salt NaCl. Several protonation constants K of the CO2− and trivalent nitrogen in III and IV have been determined. The performance evaluation as a potential antiscalant in reverse osmosis (RO) plants was examined. III containing acid motifs of –PO3H2 at a concentration of 15 ppm demonstrated remarkable efficiency of ≈100% in inhibition of CaSO4 scale from its supersaturated solution for several days at 40 °C, while precipitation occurred within 10 min in the presence of 20 ppm of IV containing ester motifs of –PO3Et2.