New pH sensitive network: Combination of an amphiphilic degradable polyester with a β‐cyclodextrin copolymer

A novel hydrophobic monomer, ethyladamantyl malolactonate, has been synthesized and copolymerized with benzyl malolactonate by anionic ring‐opening polymerization. The ratio of adamantyl monomer varied from 0 to 100 mol%. Deprotection of benzyl groups leads to a water soluble copolyester with carboxylic acid lateral functions which give a polyelectrolyte character to the corresponding polymers. The mixture of a copolyester containing 10% of adamantyl groups and a β‐cyclodextrin/epichlorohydrin copolymer in aqueous solution leads to a new pH‐dependant associating system. The solution behavior of this system was studied by viscosimetry as a function of pH, concentration and ratio of both copolymers. At the initial solution pH (pH=2), the copolyester adopts a coiled structure as a result of hydrophobic interactions between the pendant adamantyl groups. Consequently, no network formation is observed as shown by a very low viscosity. As the pH increase, the viscosity of the medium increases and reaches a maximum at pH=5. At this pH, the copolyester expands because of electrostatic repulsions between the carboxylate pendant functions. Consequently, the adamantyl groups are accessible and can be encapsulated into the β‐cyclodextrin cavities resulting in a significant increase of the viscosity.