Solid-state structure of polypeptide-based rod-coil block copolymers: folding of helices

This work compares the solid-state structures of films made from a polystyrene-poly(Z-L-lysine) (1) and a polystyrene-poly(gamma-benzyl-L-glutamate) (2) block copolymer, both having virtually the same numbers of repeating units and block length ratios. Small-angle X-ray scattering (SAXS) revealed a hexagonal-in-undulated lamellar morphology for both films. The long-period and the thickness of layers obtained for 2 were by a factor of three smaller as compared to 1, indicating that PBLGlu helices were folded twice, whereas PZLLys helices were fully stretched. Another difference shows up in the packing of helices, the level of ordering being considerably lower in 2. This might be due to spatial restrictions in the proper alignment of back-folded helical segments.