Synthesis, Characterization, and Aqueous Solution Behavior of Electrolyte- and pH-Responsive Carboxybetaine-Containing Cyclocopolymers

Abstract

A novel pH- and salt-responsive carboxybetaine monomer, 4-(N,N-diallyl-N-methylammonio)butanoate (2), was prepared and cyclocopolymerized with the cationic monomer N,N-diallyl-N,N-dimethylammonium chloride (3) in 0.5 M NaCl aqueous solution (pH = 7.0) using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The molar feed ratio of 2:3 was varied from 100:0 to 0:100 with the total monomer concentration held constant at 2.5 M. Cyclopolymerization to five-membered ring structures common to diallylammonium salts was confirmed by 13C NMR spectroscopy. Reactivity ratio studies indicate that 2 and 3 copolymerize in a nearly ideal fashion (r1 = 0.86, r2 = 0.99). Weight-average molecular weights and second virial coefficients vary from (6.0 to 12.8) × 104 g mol-1 and (1.62 to 5.36) × 10-4 mL mol g-2, respectively. Dilute solution viscosity behavior depends on copolymer composition, ionic strength, and pH. Copolymers with a large excess charge exhibit typi...