Block copolymers with a polyvinyl and a polypeptide block: factors governing the folding of the polypeptide chains

Abstract

AB block copolymers polystyrene-poly(γ-benzyl- l-glutamate) (SG) of various molecular weights and compositions were synthesized and studied by X-ray diffraction and infra-red spectroscopy. They exhibit lamellar mesophases in the solid state and in dioxane concentrated solution. Each sheet of the lamellar structure results from the superposition of two layers: one formed by the polyvinyl chains in a disordered conformation, the other formed by the polypeptide chains in an α-helix conformation arranged in a hexagonal array and generally folded. The comparison of the lamellar structure of copolymers polystyrene-poly(γ-benzyl- l-glutamate) (SG), polybutadiene-poly(γ-benzyl- l-glutamate) (BG) and polystyrene-poly(ε-carbobenzoxy- l-lysine) (SCK) showed that: (1) for the three types of copolymers (copolymers SG or BG or SCK) the number of folds of the polypeptide chains increases with the molecular weight of both the polyvinyl and the polypeptide blocks; (2) for copolymers of fixed molecular weight of the polyvinyl block and fixed degree of polymerization of the polypeptide block the number of folds of the polypeptide chains depends upon the nature of both the polyvinyl and the polypeptide blocks: a polypeptide chain is more folded when it is linked to a polystyrene chain than to a polybutadiene chain but a poly(ε-carbobenzoxy- l-lysine) chain is more rigid than a poly(γ-benzyl- l-glutamate) chain.