Nanostructure formation in poly(γ-benzyl-l-glutamate)–poly(ethylene glycol)–poly(γ-benzyl-l-glutamate) triblock copolymers in the solid state

Abstract

The morphology in the solid state of a series of triblock copolymers comprising a poly(ethylene glycol) (PEG) midblock and symmetric poly(γ-benzyl-L-glutamate) (PBLG) end blocks has been studied using X-ray scattering and microscopy techniques. Transmission electron microscopy (TEM) on samples selectively stained with uranyl acetate provided clear assignment of morphologies for as-cast and annealed samples. The thickness of both PEG and PBLG domains was in good agreement with calculations based on the conformations of the respective chains, allowing for the crystal or amorphous state of PEG and the α-helical or β-sheet structure of the PBLG. Atomic force microscopy provided complementary information on surface morphology for several samples that was in good agreement with the structure observed by TEM. A morphology diagram was constructed. Cylindrical structures were observed for ordered samples with low f_PBLG, whereas at higher f_PLBG there was evidence for broken lamellar and “hockey puck” nanostructures. Regular lamellae were observed for intermediate compositions.