Polymers of malic acid conjugated with the 1-adamantyl moiety as lipophilic pendant group

Ethyladamantyl malolactonate and butyladamantanamide malolactonate were prepared, starting from malic acid, following the usual synthesis route described for different malolactonic acid esters. Despite the steric hindrance of both adamantyl groups, the three-step synthesis led to the corresponding lactones with a quite good yield and high purity. Otherwise, ethyladamantyl malolactonate has been obtained by chemical modification of the lateral carboxylic acid function of malolactonic acid. Both ethyladamantyl malolactonate and butyladamantanamide malolactonate were homopolymerized by anionic ring opening polymerization using tetramethylammonium benzoate as initiator. Expected high molecular weight homopolymers were obtained and characterized by H-1 nuclear magnetic resonance (n.m.r.) and size exclusion chromatography (s.e.c.). Furthermore, ethyladamantyl malolactonate was copolymerized with benzyl malolactonate in the molar ratio 5/95. The resulting copolymer was studied by H-1 and C-13 n.m.r., s.e.c. and differential scanning calorimetry. After deprotection of the benzyl protecting groups by catalytic hydrogenolysis, the corresponding poly(beta-malic acid-co-ethyladamantyl beta-malate) displayed a water solubility. (C) 1997 Elsevier Science Ltd.