Alternate copolymerization of diallylamine derivatives [(CH₂CH–CH₂)₂NR; R = Me, (CH₂)₃PO(OEt)₂, and CH₂PO(OEt)₂] (I)–maleic acid (MA) and (I·HCl)–SO₂ pairs have been carried out thermally using ammonium persulfate initiator as well as UV radiation at a λ of 365 nm. The reactivity ratios of ≈0 for the monomers in each pair I–MA and I·HCl–SO₂ ensured their alternation in each copolymer. However, numerous attempted terpolymerizations of I–MA–SO₂ failed to entice MA to participate to any meaningful extent. In contrast to reported literature, only 1–2 mol% of MA was incorporated into the polymer chain mainly consisting of poly(I-alt-SO₂). Quaternary diallyldialkylammonium chloride [(CH₂CH–CH₂)₂N⁺R₂Cl⁻; R = Me, Et] (II) also, did not participate in II–MA–SO₂ terpolymerizations. Poly((I, R = Me)-alt-SO₂) III is a stimuli-responsive polyampholyte; its transformation under pH-induced changes to cationic, polyampholyte-anionic, and dianionic polyelectrolytes has been examined by viscosity measurements. The pK_a of two carboxylic acid groups and NH⁺ in III has been determined to be 2.62, 5.59, and 10.1. PA III, evaluated as a potential antiscalant in reverse osmosis plants, at the concentrations of 5 and 20 ppm, imparted ≈100% efficiency for CaSO₄ scale inhibition from its supersaturated solution for over 50 and 500 min, respectively, at 40 °C. The synthesis of PA III in excellent yields from cheap starting materials and its very impressive performance may grant PA III a prestigious place as an environment-friendly phosphate-free antiscalant.