Chain dimensions in free and immobilized brush states of polysulfobetaine in aqueous solution at various salt concentrations

The chain dimensions of free and immobilized polysulfobetaine in aqueous solution at various salt concentrations were investigated by size-exclusion chromatography with multiangle light scattering and neutron reflectivity measurement, respectively. The dependence of the z-average mean square radius of gyration (<S²>_z^1/2) on the weight-average molecular weight (M_w) of free poly(3-(N-2- methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfo-nate) (MAPS) in aqueous solution at salt concentrations of 74, 100, 200, and 500 mM was described by the perturbed wormlike chain model using the chain stiffness parameter λ^-1 the molar mass per unit contour length ML, and the excluded volume effect B. B increased from 0 to 1.8 nm with increasing salt concentration to 500 mM due to the screening of attractive electrostatic interaction between ammonium cations and sulfonyl anions by salt ions. The swollen structure of the poly(MAPS) brush in D₂O changed from a shrunken state to a relatively extended state with increasing salt concentration from 0 to 500 mM NaCl/D₂O solution. The thickness of the swollen poly(MAPS) brush in 500 mM NaCl/D₂O was 9.0 times greater than 2<S²>_z^1/2 of free poly(MAPS) due to high osmotic pressure generated by the excluded volume effect of densely grafted polymer chains.