Amphipathic block copolymers with two polypeptide blocks: Synthesis and structural study of poly(N ε-trifluoroacetyl- l-lysine)-polysarcosine copolymers

Abstract

AB block copolymers of poly(N ε- trifluoroacetyl- l-lysine)-polysarcosine (KtSa) were synthesized and studied by X-ray diffraction. In order to obtain copolymers with a polydispersity small enough to allow the formation of mesophases, the first block of poly(N ε- trifluoroacetyl- l-lysine ) was fractionated before using it as a macromolecular initiator of the polymerization of the second block of polysarcosine. Block copolymers of KtSa exhibit lamellar mesophases in the solid state and in concentrated aqueous solution. Each sheet of the lamellar structure results from the superposition of two layers: one formed by the hydrophilic polysarcosine chains in a disordered conformation, the other formed by the hydrophobic poly(N ε- trifluoroacetyl- l-lysine ) chains in an α-helix type conformation arranged in a hexagonal array and tilted. The influence of the water content of the mesophase and of the composition of the copolymers on the structural parameters of the lamellar structure was analysed and it was shown that the angle of tilt of the poly(N ε- trifluoroacetyl- l-lysine ) helices increases with both the water content of the mesophases and the length of the polysarcosine chains.