Supramolecular Cyclization Behavior of Rodlike Micelles Assembled from Polypeptide Triblock Copolymers
Poly(γ-benzyl-L-glutamate)-block-poly(ethylene glycol)-block-poly(γ-benzyl-L-glutamate)(PBLG-b-PEG-b-PBLG)triblock copolymers were synthesized using amine-PEG-amine(NH2-PEG-NH2)as macroinitiator via ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride(BLG-NCA).The molecular weight and molecular weight distribution of the polymers were characterized by proton nuclear magnetic resonance spectroscopy(1H-NMR)and gel permeation chromatography(GPC).Rodlike micelles were assembled from the PBLG-b-PEG-b-PBLG triblock copolymers using a mixture of tetrahydrofuran and N,N-dimethylformamide(THF-DMF)as initial solvent.The PBLG segments are perpendicular to the long axis in the rodlike micelles.Under THF addition,the rodlike micelles bend to form curved rodlike micelles and then toroid micelles.The morphology and structure of the assemblies were characterized using scanning electron microscopy(SEM),transmission electron microscopy(TEM),and dynamic light scattering(DLS).The degree of bending of the nanorods can be adjusted by variation of the polymer molecular weight,toroid forming time,temperature,and THF adding content.The degree of polymerization of PBLG segments affects the diameter of rodlike micelles.The aspect ratio of the rodlike micelles determines whether supramolecular cyclization occurs.The addition of THF and the increase of temperature promote the occurrence of supramolecular cyclization behavior.The effect of temperature on supramolecular cyclization behavior exhibits a certain degree of reversibility.CD spectra were employed to characterize arrangement of the phenyl rings in the PBLG segments,revealing that the contraction of the phenyl rings induced by THF is the driving force for the bending of the nanorods.The research mimicking the hierarchical self-assembly strategy in preparing complex structures by biosystems,reported a step-wise self-assembly of polypeptides into nanotoroids.The study enriches the preparation method for polymer nanotoroids,and will guide the controlled preparation of nanotoroids as well as their functional applications.
Polypeptide copolymersHierarchical self-assemblyRodlike micellesSupramolecular cyclizationPhenyl ring arrangement
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