Synthesis and application of alternate cyclopolymers of β-diallylaminoethyliminodiacetic acid with maleic acid and sulfur dioxide

Bis-cationic monomer β-diallylaminoethyliminodiacetic acid dihydrochloride (I) underwent alternate cyclocopolymerizations with SO₂ and maleic acid to give poly(bis-zwitterion) (PBZ) (± ±) II, and III, respectively. The PBZs contained the chelating motifs of [NH⁺(CH₂)₂NH⁺(CH₂CO₂⁻)₂] embedded in the pyrrolidine ring of each repeating unit. Both the PBZs were water-insoluble, however they became water-soluble with assistance from salts like NaCl. PBZs II and III, having the point of zero charge at pH 2.4, became water soluble outside the pH-windows of 0.81–4.46 and 1.49–3.35, respectively, whereby the electroneutral pH-responsive polymers become charge-imbalanced. The ‘apparent’ pK_as of the protonated amine centers in II were found to be 5.18 and 9.92. As an antiscalant, PBZ III (2.5 ppm) demonstrated inhibition of CaSO₄ scale formation with 99% efficacy for over 180 min, while at 1.5 ppm inhibition efficiency was found to be 98% for 50 min. PBZ II at concentrations of 20 and 10 ppm demonstrated CaCO₃ scale inhibition of 98% for over 240 min and 95% for over 90 min, respectively. A synergistic mixture of III (20 ppm) and KI (400 ppm) arrested corrosion of mild steel in 1 M HCl with a remarkable efficacy of 98% for 24 h at 60 ^οC.