Study On The Synthesis And Properties Of Mikto-arm Star Polymer Based On Sydnone-maleimide Chemistry

As the most important kind of branched polymer, star polymer is famous for its low degree of crystallinity, low melt viscosity, low hydrodynamic radius, good solubility and higher reaction activity. It is considered to be one of materials that can break through the limitations of human society faced now in many fields which impacts human life deeply, such as, the biological medicine, electrolyte and many new advanced functional material application fields. Due to the fantastic properties, star polymer has been the focus of researchers in decades of years. However, it is very difficult and complex to prepare star polymer especially miktoarm star polymer. So, it is of profound significance to develop new strategy to make the synthesrs of star polymers easy and efficient, especially to prepare the star polymers with exact structure and excellent properties. These studies will enrich the theory of fundamental polymer chemistry research and broaden the application of polymer material. Besides, though the self-assembly behavior of block copolymer has been extensively studied, star polymer's self-assembly still remains a shortcoming in polymer self-assembly science. A lot of meaningful work deserved to be done in the study of self-assembly of star polymer to perfect the polymer self-assembly theory. Fuethermore, the efforts carried on studying the loading capacity of star polymers' assemblies will accelerate the application of star polymer carriers in biological medicine.Sydnone shows the special property in the reaction with maleimide, one molecular sydnone can react with two molecules maleiminde via two 1,3 dipolar cycloaddition. The Sydnone-Maleimide-Dipolar-Cycloaddion (SMDC) matches Click-Chemistry' rule. Benefited from SMDC, a serious amphiphilic A2B2 star polymer based on the polyethylene glycol chain (PEG) and polycaprolactone chain (PCL) has been designed and successfully prepared in this study. In addition, by using the chain excitation method, A2(B-b-C)2 star polymer with thermo-responsive poly n-isopropyl acrylamide chain (PNIPAM) has been synthetized. A few efforts has been spent on the study of the relationship between the synthesized polymer's structure and their self-assembly properties. The details are divided into three parts as follows:1) As an initial approach to the synthesis of the star polymers of interest, attempts were made to optimize the existing synthetic pathway by introducing the 1,3 dipolar cycloaddition reaction between sydnone and maleimide group (SMDC) for the first time. Firstly, by using the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC), a set of reactive arms (mPEG-FM-OH) bearing a maleimide group and a hydroxy was synthesized, followed with the combination of the ring-opening polymerization (ROP) with caprolactone and SMDC reaction with sydnone at the same time to prepare the target A2B2 miktoarm star polymer, calling the "One-pot method". Moreover, the set of target A2B2 star polymers were also prepared by the so-called "Coupling-into method" and "In-out method". These methods were compared and studied to demonstrate the benefits brought by the SMDC and determine the optimum preparation conditions. In addition, the factors that can influent polymer structure were analyzed too. Besides, how star polymers'structure affect its crystallization was also discussed.2) With an effort to prepare star polymers with block arms, the chain extension method was employed by introducing the trithiocarbonate group, the most effective RAFT agents(Reversible Addition-Fragmentation Chain Transfer Polymerization), into the A2B2 star polymers prepared already, which can initiate the polymerization of NIPAM monomer to get the target thermos-responsive A2(B-b-C)2 star polymers. It was proved that the post treatment of the A2B2 miktoarm star polymer prepared by SMDC is a feasible approach to get more complex structure star polymer. And the relationship between structures and properties, such as hydrophilic segment content ratio and hydrophobic segment content ratio, and thermal and pH responsive behaviors has been studied.3) To investigate star polymers' self-assembly process, a novel model was established to illustrate how the polymer chain moves during the assembly process, which helps to understand the formation of the final rod-like assemblies. And the gold nano-particles were used as the model guest to test the loading capacity of star polymers' assemblies in water, which shows the perfect transport and load capacity.