Self-associations and temperature dependence of aqueous solutions of zwitterionically modified N-isopropylacrylamide copolymers

Thermosensitive copolymer solutions are prepared from various molar ratios of N-isopropylacrylamide (NIPAM) and the zwitterionic monomer N-(methacryloxypropyl)-N,N-dimethyl-N-(3-sulfopropyl) ammonium betaine (Zw) by free radical polymerization. In the current study, we examined the rheological properties of poly (NIPAM/sulfobetaine) copolymer solutions. We found that the rheological properties are conceptually linked with the copolymer chemical structure and chain topology. We also report the effects of bulk molar mass and zwitterions on flow curve ɳ (γ⋅$$ \overset{\cdot }{\upgamma} $$). With the introduction of the charged group in the PNIPAM-chain, its viscoelastic phase behavior and lower critical solution temperature (LCST) are affected. At varying concentrations of zwitterionic copolymer, they showed a shear thinning behavior with two relaxation regimes for entanglement relaxation and zwitterionic interaction. Interestingly, the zwitterionic interactions are related to the molar concentration of zwitterionic monomer. This is eventually associated with the topology of the copolymer chain. Our results also showed that there was a linear increase in the LCST of these solutions as a function of zwitterionic moieties.