Synthesis of Well-Defined Graft Copolymers by Combination of Enzymatic Polycondensation and Click Chemistry

Aliphatic polyesters having pendant azide groups were prepared by enzymatic polycondensation in the presence of lipase from Candida antarctica type B (CAL-B). The grafting reaction to the N-3-functional polyester was carried out quantitatively at room temperature using copper-catalyzed azide-alkyne cycloaddition (CuAAC, click reaction) with monoalkyne-functional poly(ethylene oxide) (alkyne-PEO, M-n = 750 g/mol). Furthermore, both enzymatic polycondensation and click reaction were carried out successfully in sequential one-pot reaction. The graft copolymer was surface-active and self-assembled in water. The graft copolymer had a critical aggregation concentration (cac) of 3 x 10(-2) mu M in water determined by surface tension measurements. Above cac, the graft copolymer formed single chains and aggregates having a hydrodynamic radius of similar to 75 nm. Furthermore, the surface activity of the polymers at the air-water interface was studied by Langmuir trough measurements. The Langmuir isotherm of the graft polymer showed a pseudoplateau resulting from desorption of PEO chains into the subphase upon compression.