Synthesis, solution properties and scale-inhibiting behaviour of a diallylammonium/sulfur dioxide cyclocopolymer bearing phospho- and sulfopropyl pendents

Zwitterion (Z) monomer 3-[diallyl{3-(diethoxyphosphoryl)propyl}ammonio]propane-1-sulfonate underwent cyclocopolymerization with sulfur dioxide to give a new alternating copolymer poly(Z-alt-SO₂) in excellent yield (ca 90%). The polyzwitterion (±) (PZ) (i.e. poly(Z-alt-SO₂), bearing a diethylphosphonate as well as a sulfonate functionality in each repeat unit, upon ester hydrolysis gave its corresponding pH-responsive polyzwitterionic acid (±) (PZA). The pH-induced equilibrations (+) cationic polyelectrolyte ⇌ (±) PZA ⇌ polyzwitterion/anion (± -) (PZAN) ⇌ polyzwitterion/dianion (± =) (PZDAN) permitted us to examine the effects of charge types and their densities on the interesting solubility and viscosity behaviours. The apparent protonation constants of the basic functionalities &tbond;N^±PO₃^2- in (± =) PZDAN and &tbond;N^±PO₃H^1- in (± -) PZAN in salt-free water and 0.1 mol L^-1 NaCl were determined using potentiometric titrations. (±) PZA at a meagre concentration of 20 ppm was found to be an effective antiscalant to inhibit the precipitation of CaSO₄ from its supersaturated solution: after 500 and 800 min, the respective scale inhibitions of 86 and 98% indicated its potential use as an effective antiscalant in reverse osmosis plant.