Butyl modified poly(allylamine)s with butyl substitution degrees of 15% to 70% were prepared. The polymers show pH sensitive property and lower critical solution temperature (LCST) behavior. The LCST appears at lower temperature

lower pH and lower polymer concentration for the polymer with higher butylated degree. The binding of native lysozyme with the polymers depends on the hydrophobicity of the polymers at the pH range that the protein and the polymer carry the same positive charges. The increase of polymer hydrophobicity can increase the binding with lysozyme

but the self-aggregation of the polymer decreases the binding. The bound lysozyme molecules can recover their native activity completely after the dissociation of the complexes. Compared with native lysozyme

the denatured one which exposes the hydrophobic residues can increase the binding with the polymer and form stable complex nanoparticles.