Synthesis And Characterization Of Amphiphilic Block And Star Copolymers Based On PEO And PCL

Amphiphilic and functional copolymers have attracted more interests in the last decades for their widely application in self-assembly field. Among the investigated amphiphilic block copolymers, the most utilized hydrophilic component is poly (ethylene oxide) (PEO) due to biocompatibility, lack of immunogenicity and easy clearance from the human body, especially the materials modified by PEO can keep some properties of PEO. Another kind of polymer, such as poly (ε-caprolactone) (PCL), has also been widely used as important drug delivery carriers because of their biocompatibility and biodegradability. In order to meet the increasing demands for better performances and satisfy the requirements of some specific applications, the biodegradable polymers PCL modified by PEO have attracted more and more attentions.In this paper, the block copolymers mPEO-b-PCL with different PCL segment molecular weight were successfully synthesized by the combination of living anionic polymerization and coordination-insertion ring-opening polymerization. By means of PEO-supported multifunctional-initiating system, some well-defined star-shaped copolymers PEO3-b-PCL3 and PEO4-b-PCL4 were synthesized and their properties were explored. The main results summarized as follows:(1). A series of amphiphilic block copolymers mPEO-b-PCL with different PCL segment molecular weight were successfully prepared by combination of anionic ring-opening polymerization with coordination-insertion ring-opening polymerization. Firstly, the linear mPEO was prepared by anionic ring-opening copolymerization of EO with 2-(2-methoxyethoxy) ethoxide potassium as the small molecule initiators. Then, the obtaind mPEO was used to initiate the ring-opening polymerization of CL as the macroinitiator, in the absence of Sn(Oct)2 as the catalyst, and amphiphilic block copolymers mPEO-b-PCL were successfully synthesized. By changing the ratios of monomer and macroinitiator, a series of different molecular weight mPEO-b-PCL were prepared. Meanwhile, the chemical structures, molecular weights and molecular weight Distributions of intermediates and final products were characterized by 1H NMR and GPC. The critical micelle concentration (cmc) of the copolymer was determined by using pyrene as fluorescence probe. In addition, the sizes and morphologies of the micelles with the different PCL segment lengths were investigated with laser nano-particle size analyzer (DLS) and transmission electron microscopy (TEM), respectively. The results showed that the block copolymers mPEO-b-PCL had the higher critical micelle concentration value and the smaller size of nanoparticles as the PCL segment length shorter.(2). A series of three-arm or four-arm star-shaped copolymers based on poly(s-caprolactone) (PCL) core and poly(ethylene oxide) (PEO) corona with different molecular weight were prepared by a combination of anionic ring-opening polymerization (AROP) and coordination-insertion ring-opening polymerization (CROP). Firstly, the three-arm star-shaped PEO3 and four-arm star-shaped PEO4 were prepared by AROP of EO. Then, three-arm star-shaped PEO3 and four-arm star-shaped PEO4 as the macroinitiator were used to initiate the ring-opening polymerization of CL, in the absence of Sn(Oct)2 as the catalyst, and amphiphilic star copolymers PEO3-b-PCL3 and PEO4-b-PCL4 were obtained. By changing the ratios of monomer and macroinitiator, a series of different molecular weight PEO3-b-PCL3 and PEO4-b-PCL4 were prepared. At the same time, the chemical structures, molecular weights and molecular weight Distributions of intermediates and final products were characterized by H NMR and GPC. In addition, the sizes and morphologies of the obtained micelles with the different PCL segment lengths were investigated with DLS and TEM, respectively. It was found that the self-assembly morphologies were spheric micelle...