Synthesis,Characterization And Self-Assembly Of Diblock Copolymer Based On Poly(Noctylglycines)

Polypeptoids,also referred as poly(N-substituted glycines),are an emerging class of bioinspired polymers.The polypeptoid backbone is identical to that of polypeptide,but the side chain is appended to the nitrogen rather than the α-carbon in the main chain.It thus removes inter-and intra-chain hydrogen bonding in the backbone and also eliminates the main chain chirality.Polypeptoid has many excellent properties which are different from polypeptide,and it has received extensive attention due to its good biocompatibility and biological activity as well as the good solubility and accessible thermal processability of the conventional polymers.In this paper,the synthesis,modification and self-assembly of novel polypeptoid copolymers were studied.1.A series of poly(ethylene glycol)-b-poly(N-octylglycine)(PEG-b-PNOG)amphiphilic block polymers,prepared by ring-opening polymerization(ROP),were synthesized from N-octyl N-carboxylanhydride(Oct-NCA)initiated by poly(ethylene glycol)amine(PEG-NH2)in THF.We systematically studied the thermodynamic properties of polypeptoids with different block ratios.Both PEG and PNOG blocks are crystallized and the crystallization of PEG is suppressed by incorporating PNOG block.Besides,we found that block copolypeptoids can form ultrathin two-dimensional(2D)nanosheets in solution.The 2D planar structures are achieved from hierarchical selfassembly through a sphere-to-cylinder-to-nanosheet transition pathway.The preliminary assembled spheres can behave like a fundamental packing motif to spontaneously stack into a planar lattice.We demonstrated that the evolution of crystallinity in PNOG core are the main factors in inducing the formation of 2D nanosheets.We further investigated the effects of degree of polymerization,polymer concentration,solvent,and temperature on assembly morphology.The preparation of 2D lamellar crystals by synthetic polymers has great application value in nanomaterials and biomedical fields.2.A series of poly(N-allylglycine)-b-poly(N-octylglycine)(PNAG-b-PNOG)diblock polymers,prepared by ring-opening polymerization(ROP),were synthesized from N-allyl N-carboxylanhydride(Al-NCA)and N-octyl N-carboxylanhydride(Oct-NCA)initiated by benzylamine.The oligo(ethylene glycol)(OEG3)was incorporated via click chemistry strategy to prepare a class of thermal-responsive diblock polypeptoids(PNAGg-EG3)-b-PNOG.We systematically studied the influence of block ratio and molecular weight on the thermodynamic properties of(PNAG-g-EG3)-b-PNOG.As the molecular weight decreases,the melting transition temperature decreases.With the increase of the proportion of(PNAG-g-EG3)block,the crystallization of PNOG was inhibited.We further studied the thermal-responsive behavior.(PNAG142-g-EG3)-b-PNOG23 has a good and stable reversible phase transition with a temperature transition range ΔT <5 °C.While reducing the molecular weight or increasing the proportion of PNOG block will lead to thermal-responsive behavior worse.The amphiphilic block polypeptoid can be assembled into one-dimensional nanofiber structures in aqueous solution,which the size of the nanofiber is responsive to temperature.The thermal-responsive polymer micelles have wide application prospects in the biomedical fields.