Study On The Synthesis Of Star Polymer By Tandem Ring-Opening Polymerization Of Aziridines And Click Chemistry

Star polymer has been used as a synthetic vector for gene transfection,showing enhanced gene transfection efficiency and lower cytotoxicity than a linear one.The topological structure of the polymer is one of the most critical factors.Polyethyleneimine（PEI）-based polymers are one of the most successful non-virus vectors for gene transfection.However,it is not easy to synthesize star-shaped polyethyleneimine-based polymers with controllable architectures.Therefore,developing an efficient and straightforward method for synthesizing polyethyleneimine-based polymers with star-shaped architectures is essential.In this thesis,a one-pot strategy for tandem ring-opening polymerization of N-sulfonyl aziridines and click chemistry to prepare star-shaped polyethyleneimine-based polymers has been developed.A star-shaped polyaziridine was synthesized firstly,then star-shaped polypropylenimine（PPI）will be obtained after the removal of the-Ts group.The specific work is as follows:（1）Preparation of linear polyaziridine with azide end-group.In the presence of TMSN₃and organic base,the ring-opening polymerization of Ts MAz occurred to give theα-N₃P（Ts MAz）.Kinetic experiments revealed the chain growth rate k_p that the catalyzed by different organic bases is in order:DBU>MTBD>PMDETA>DABCO.（2）One-pot tandem synthesis of star polymers.Firstly,we used TMSN₃ as the initiator,Ts MAz as the monomer,PMDETA as the organic catalyst for ring-opening polymerization.The tri-or tetra-alkynyl compound was then added as the coupling agent and CuBr as the catalyst.Star-shaped polyaziridines were successfully synthesized.PMDETA plays different roles in the tandem reaction,acting as the catalyst first for the ring-opening polymerization of N-sulfonyl aziridine,and then as a ligand to promote the click reaction.This tandem process is atom economical.（3）Removal of-Ts group to synthesize star-shaped PPI.With Red-Al as a reductive reagent,the-Ts group of star-shaped polyaziridine was removed to give 3-arm or 4-arm star-shaped PPI.The solution of star-shaped PPI has strong fluorescence,and as the proportion of inert solvent increases,it exhibits an aggregation-caused quenching（ACQ）effect.In this thesis,a new strategy for synthesizing star-shaped polyethyleneimine-based polymers by a one-pot tandem method is developed,which provides a new approach toward the star-shaped polyethyleneimine-based polymers.