4. pH-sensitive polymers

4.1 Concept

A pH-sensitive conformation, with changes in solubility, is a common behavior for biopolymers. pH-sensitive polymers are composed of ionizable polymer pendant groups that can accept and donate protons in response to changes in the pH environment. When the pH environment changes, the degree of ionization in a polymer carrying weakly ionizable groups is dramatically altered at a specific pH which is called pK _a . This rapid change in the charge of pendant groups causes an alternation in the hydrodynamic volume of polymer chains. The transition from the contracted to the expanded state is explained by the osmotic pressure exerted by mobile counterions, which neutralize the lattice charges.