Poly(N,N-diallylaspartic acid-alt-sulfur dioxide): its synthesis and application

Monomer pairs, dimethyl N,N-diallylaspartate hydrochloride [(CH₂=CH–CH₂)₂NH⁺CH(CO₂Me)CH₂CO₂Me Cl⁻] (I)/SO₂ and N,N-diallylaspartic acid hydrochloride [(CH₂=CH-CH₂)₂NH⁺CH(CO₂H)CH₂CO₂H Cl⁻] (II)/SO₂, underwent alternate cyclocopolymerization to give cationic polyelecyrolytes (CPEs), poly(I-alt-SO₂) (III) and poly(II-alt-SO₂) (IV), respectively, in very good yields. (+) III upon acid hydrolysis was converted to cationic (+) IV, bearing in each repeating unit the triprotic acid residues [(NH⁺…(CO₂H)₂] of aspartic acid hydrochloride. Under the influence of pH, (+) IV has been equilibrated to water-insoluble diprotic polyzwitterionic acid (±) V, water-soluble monoprotic poly(zwitterion-anion) (± −) VI and finally its conjugate base polydianion (=) VII. Basicity constants of CO₂ ⁻ and amine group have were determined. The pH-responsive polymer was demonstrated to be an efficient antiscalant against CaSO₄ scaling. For potential separation and purification of biomolecules, a recyclable aqueous two-phase system (ATPS) was constructed using water-soluble (=) VII and urethanized polyvinyl alcohol; the ionic polymer can be recycled by precipitating it as (±) V at a lower pH.