Water-Soluble Polymers. 77. Amphoteric Cyclocopolymers with Sulfobetaine Units: Phase Behavior in Aqueous Media and Solubilization of p-Cresol in Microdomains

Abstract

A novel series of cyclocopolymers containing the pH-responsive hydrophobic monomer, N,N-diallyl-N-methylamine (DAMA), and the sulfobetaine monomer, 3-(N,N-diallyl-N-methylammonio)-propanesulfonate (DAMAPS), have been prepared in 0.5 M NaCl aqueous solution (pH = 4.0) using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The feed ratio of DAMA:DAMAPS was varied from 100:0 to 0:100 mol % with the total monomer concentration held constant at 2.5 M. 13 C NMR data indicate that the resulting polymers maintain the five-membered-ring structure in the cis conformation common to cyclized diallylammonium salts. Reactivity ratio studies predict that the sulfobetaine monomer is incorporated randomly along the polymer backbone. Weight-average molecular weights and second virial coefficients vary from (4.00 to 8.42) x 10 4 and (2.14 to 4.62) x 10 -4 mL mol g -2 , respectively. Solution behavior is dependent upon pH as determined by turbidimetric titration, steady-shear viscometry, and equilibrium surface tensiometry. At high degrees of ionization, the copolymers assume an extended conformation due to the charge-charge repulsions along the copolymer backbone. As the molar incorporation of the sulfobetaine increases, the copolymer assumes a more globule-like conformation due to zwitterionic interactions. With decreasing degree of ionization of the DAMA units, hydrophobic associations increasingly dominate the solution behavior. For copolymers with a low incorporation of the sulfobetaine, chain collapse leading to phase separation occurs. However, at higher incorporations, the sulfobetaine acts as a hydrophilic segment to limit hydrophobic packing and minimizes the chain collapse. Equilibrium dialysis experiments demonstrate that these pH-reversible microdomains can be used to control the sequestration of organic foulants and thus have potential application as polymeric surfactants in micellar enhanced ultrafiltration processes for water purification.