Small-angle neutron scattering from diblock copolymer poly(styrene-d8)-b-poly(γ-benzyl L-glutamate) solutions: Rod-coil to coil-coil transition

The elastic properties of rod-coil diblock copolymer poly(styrene-d8)-b-poly(γ-benzyl L-glutamate) (PSd-b-PBLG) rod-coil diblock copolymer solutions were investigated using small-angle neutron scattering (SANS). PBLG is known to undergo a transition from a rodlike α-helical secondary structure to a random coil conformation under specific solvent conditions: the PBLG is (i) rodlike in dioxane and (ii) random coil in dioxane/trifluoroacetic acid (80/20). For the PSd-b-PBLG diblock copolymer, this conformational transition results in a topological change from a rod-coil to a coil-coil type structure. SANS results indeed show the presence of the expected scattering peaks-copolymer signature-for both conformational topologies. The position and the height of these scattering peaks are found in good agreement with a recent theoretical model that describes the conformational change in rod-coil diblock copolymer solutions. Circular dichroism experiments confirmed the change in secondary structure in the peptide block that accompanies the topological transition observed by SANS.