Block and graft copolymers made of 16-membered macrolactones and l-Alanine: a comparative study

Abstract

Block and graft poly(macrolactone)-poly(a-amino acid) copolymers made of l-alanine and pentadecalactone or globalide respectively, are prepared. A sequential ring-opening polymerization (ROP) copolymerization route consisting of two stages, the first devoted to the preparation of the amino-functionalized poly(macrolactone) and the second to the amino-initiated polymerization of l-alanine N-carboxyanhydride (Ala-NCA), is followed for the synthesis of both types of copolymers. Poly(l-alanine) segment lengths are accurately controlled by adjusting the macroitiator/Ala-NCA ratio used for reaction in the second stage. Block copolymers are semicrystalline with the poly(pentadecalactone) block crystallizes well in a separate phase and the poly(a-amino acid) block arranged in either the a-helical or ß-sheet structure in a ratio that is depending on composition and temperature. Graft copolymers are amorphous but with the poly(a-amino acid) side chains arranged in a more or less regular conformation. Nanoparticles with a diameter of around 300 nm and moderate positive Z-potential can be obtained from the block copolymers by self-assembling in water whereas graft copolymers are unable to render recognizable objects of nanometer-dimension under similar conditions.