Design And Synthesis Of Amphiphilic Triblock Copolymers Based On ATRP And Click Chemistry

Currently more and more researches focused on synthesis of block copolymers containing MPEO blocks.Compared with some homopolymers,MPEO possesses outstanding biological and physical chemical properties,such as amphiphilic, nontoxicity,biocompatibility,crystalization and absense of antigenicity and immunogenicity, so as to be widely used in biomedical and pharmaceutical applications.Three series of triblock copolymers MPEO-PS-PCL,MPEO₄₅-PS-PBLG,MPEO₄₅-PSMPEO₁₁₄, which are composed of MPEO blocks were successfully prepared by the combination of different kinds of polymerization technologies in this article, [Mn(MPEO₄₅)=2000,Mn(MPEO₁₁₄)=5000].The structure of triblock copolymers and their precursors were characterized by the combination techniques consisting of IR, NMR and GPC.The details are as follows:1.Atom transfer radical polymerization(ATRP),ring-open polymerization and "click" chemistry were combined to synthesize a series of well-defined amphiphilic triblock copolymers MPEO-PS-PCL,the synthetic approach is presented in the following steps:First,bromine-terminated diblock copolymer MPEO-PS were prepared by the atom transfer radical polymerization of styrene initiated with macro-initiator MPEO-Br,which was obtained from the esterification of 2-bromo-2-methylpropionyl bromide and poly(ethylene oxide)monomethyl ether; Second,azide-terminated diblock copolymers were obtained through the bromine substitution reaction with sodium azide;Third,propargyl-terminated poly(ε-caprolactone)was prepared by ring-open polymerization ofε-CL in toluene with Sn(Oct)₂ as a catalyst and propargyl alcohol as an initiator;Finally,using a click reaction,the azido-terminated precursors MPEO-PS-N₃ and the propargyl-terminated PCL were successfully reacted to give the novel linear triblock copolymers MPEO-PS-PCL in the presence of a catalyst system of CuBr and N,N,N′,N″,N″-pentamethyldiethylenetriamine(PMDETA)in DMF at room temperature.2.NCA-BLG was obtained via the cyclic reaction of BTC and BLG,which was obtained from the esterification between glutamic acid and benzyl alcohol.Then propargyl-terminated PBLG was prepared via anionic ring-open polymerization of monomer NCA-BLG initiated by propargyl amine.A series of biodegradable triblock copolymers MPEO₄₅-PS-PBLG which has different molecular weight were finally obtained through the general procedure of "click" reaction that was carried out between propargyl-terminated PBLG and azido-terminated precursors MPEO₄₅-PSN₃ in the catalyst system of CuBr/PMDETA in DMF.3.Propargyl-terminated MPEO₁₁₄was prepared in the basic condition of propargyl alcohol and 4-toluenesulfonyl-terminated MPEO₁₁₄,which was obtained through esterification of MPEO₁₁₄and 4-toluenesulfochloride in the presence of pyridine. Amphiphilic ABA′type triblock copolymers MPEO₄₅-PS-MPEO₁₁₄were synthesized via a click reaction of the azide-terminated diblock copolymers MPEO₄₅-PS-N₃ and the propargyl-terminated MPEO₁₁₄in the presence of CuBr/PMDETA catalyst system in DMF.It was not reported so far concerning the synthesis of asymmetric ABA′type triblocck copolymers in such simple method.The polydispersity of the three series of copolymers is very low,which is about 1.03～1.2.