NEW PH SENSITIVE NETWORK - COMBINATION OF AN AMPHIPHILIC DEGRADABLE POLYESTER WITH A BETA-CYCLODEXTRIN COPOLYMER

A novel hydrophobic monomer, ethyladamantyl malolactonate, has been sy nthesized and copolymerized with benzyl malolactonate by anionic ring- opening polymerization. The ratio of adamantyl monomer varied from 0 t o 100 mol%. Deprotection of benzyl groups leads to a water soluble cop olyester with carboxylic acid lateral functions which give a polyelect rolyte character to the corresponding polymers. The mixture of a copol yester containing 10% of adamantyl groups and a beta-cyclodextrin/epic hlorohydrin copolymer in aqueous solution leads to a new pH-dependant associating system. The solution behavior of this system was studied b y viscosimetry as a function of pH, concentration and ratio of both co polymers. At the initial solution pH (pH=2), the copolyester adopts a coiled structure as a result of hydrophobic interactions between the p endant adamantyl groups. Consequently,no network formation is observed as shown by a very low viscosity. As the pH increase, the viscosity o f the medium increases and reaches a maximum at pH=5. At this pH, the copolyester expands because of electrostatic repulsions between the ca rboxylate pendant functions. Consequently, the adamantyl groups are ac cessible and can be encapsulated into the beta-cyclodextrin cavities r esulting in a significant increase of the viscosity.