Mesomorphic Order in Block Copolymers from α-Amino Acids and Other Monomers and in Copolymers from α-Amino Acids

Abstract

The structure of random and block copolymers of two α amino acids, and of block copolymers with an amino acid block and a carbohydrate or a vinyl block have been studied by X-ray diffraction, electron microscopy, infrared spectroscopy and circular dichroism. Copolymers with a hydrophilic carbohydrate block and a hydrophobic polypeptide block exhibit in DMSO solution and in the dry state a lamellar structure ; this lamellar structure consists of plane, parallel, equidistant sheets ; each sheet results from the superposition of two layers : one formed by the carbohydrate chains in a disordered conformation, the other formed by the polypeptide chains in an helical conformation and assembled in a hexagonal or a centred rectangular lattice. Copolymers with a polyvinyl block (polystyrene or polydiene) and a hydrophobic polypeptide block exhibit a lamellar structure similar to that of copolymers with a carbohydrate and a peptide block, except that their polypeptide chains in an helical conformation are always hexagonally packed and are generally folded. For random and block copolymers of benzyl-L-glutamate and one of the following amino acids, ε-carbobenzoxy-L-lysine, L-leucine in the dry state and in dioxane concentrated solution the polypeptide chains are always in an helical conformation, but they are assembled on an hexagonal or a centred rectangular lattice depending upon the type of copolymer (random or block), the nature of the blocks and the copolymer composition.