Synthesis of stimuli-responsive ionic cyclopolymers in search of phosphorous-free antiscalants

Ammonium persulfate-initiated cyclopolymerization of maleic acid (HO₂CC=CCO₂H) (MA) with diallylamine (–NR₂, R = CH₂ = CH-CH₂) derivatives (DADs): R₂NH⁺CH₂CO₂⁻ (I), R₂NCH₂CO₂⁻Na⁺ (II), R₂NCH₂CO₂Et (III), R₂NH⁺(CH₂)₃CO₂⁻ (IV), R₂N(CH₂)₃CO₂Et (V), R₂NH⁺(CH₂)₃SO₃⁻ (VI) and R₂N(CH₂)₃SO₃⁻Na⁺ (VII) gave a series of new pH-responsive alternate copolymers: –[(DAD-alt-MA)]_n– VIII-XIV, respectively. Homopolymers XV and XVI of the corresponding monomers IV and V·HCl were also synthesized. The evaluation of the synthesized polymers as potential antiscalants in reverse osmosis (RO) plants was examined. An effective scale inhibitor must arrest the formation of scale for a residence time (≈15 min) of feed water in the RO chamber. R₂NH⁺(CH₂)₃CO₂⁻ (IV)-alt-MA copolymer XI at a concentration of 5 ppm imparted 99% scale inhibition for 360 min, while at 2.5 and 1 ppm concentrations, the CaSO₄ scale inhibitions were found to be 99% and ≈ 100% during 120 and 20 min, respectively, at 40°C. Homopolymers XV and XVI, at a 20-ppm concentration, demonstrated ≈ 95% efficiency in inhibiting mild steel corrosion in 1 M HCl. In some important oilfield applications, requirement of simultaneous scale and corrosion inhibition make these polymers potential candidates for desalination and oilfield applications.