Benzyl β-malolactonate: Synthesis, copolymerization and design of novel biodegradable macromolecular surfactants

Racemic [R,S] benzyl β-malolactonate monomer (MLABz) was synthesized according to the well-established "aspartic acid" route and purified to such an extend that it allowed the controlled synthesis of poly([R,S] β-malic acid)-b-poly((D,L)-lactide) diblock copolymers by a versatile three-step pathway combining anionic and coordination-insertion ROP of MLABz and lactide monomers, respectively. For the sake of comparison, amphiphilic poly([R,S] β-malic acid)-b-poly(ε-caprolactone) diblock copolymers of identical composition were synthesized as well. The associating behavior of monodisperse diblock copolymers consisting of water-soluble poly(β-malic acid) block and hydrophobic polylactide or poly(ε-caprolactone) block was studied in aqueous solution. Accordingly, both types of copolymers were dissolved directly in water and (dynamic) surface tension measurements were carried out. It came out that poly(β-malic acid)-b-poly((D,L)-lactide) amphiphilic diblock copolymers showed tensioactive properties with a lower critical micellar concentration, a higher efficiency of adsorption and a better monomer coefficient diffusion compared to corresponding poly(β-malic acid)-b-poly(ε-caprolactone) diblock copolymers of comparative composition.