Study On Synthesis, Characterization And Properties Of Hexa-Armed Star Polymers With A Hexafunctional Cyclotriphosphazene Core

As one of the simplest branched polymer,star polymers possess specific three-dimensional structures and properties and have the ability to self-assemble in bulk and in solution forming a range of different morphologies as their linear polymer counterparts.These resultant aggregates have very interesting particular properties,so star polymers have many potential applications in areas such as drug delivery systems,biology,separating materials,optoelectronic materials and supports of catalysts and have became an important research topic in the field of supramolecular chemistry.Cyclotriphosphazenes possess a special and high symmetrically structures are an interesting class of materials exhibiting useful thermal,biological,chemical and epitaxial crystallization properties and are excellent models for structure-reactivity studies at a macromolecular level.In this paper,progress in synthesis and self-assembly of star polymers was reviewed.A novel hexaarmed cyclotriphosphazene initiator was prepared by the reaction of hexachlorocyclotriphosphaneze with series reagents and hexa-armed star polymers with a hexafunctional cyclotriphosphazene core were prepared and characterized.The self-assembly behaviors of the resultant star polymers in solvents were investigated.A bromine-terminated cyclotriphosphazene atom transfer radical polymerization(ATRP) initiator with six initiating sites was synthesized by the reaction of hexachlorocyclotriphosphaneze with a series of reagents.Star polystyrene(Star-(PS)₆),star poly(methyl methacrylate) (Star-(PMMA)₆)and star poly(t-butyl methacrylate)(Star-(PtBMA)₆)were synthesized via the ATRP using bromine-terminated cyclotriphosphazene as initiator.It was found that the resultant polymers could form various morphologies in solvents by varying the molecular weight,solvent and concentration.Star-(PS)₆ can self-assembly into plates,plates with some small pores arranged orderly around the circumference of it,hollow plates and large spheres aggregates in THF by varying the molecular weight of the Star-(PS)₆,while Star-(PS)₆ can form porous flat film in CHCl₃ and large spheres aggregates in 1,4-dioxane.The concentration of the star polymer can change the dimension of the aggregates formed.Star-(PMMA)₆ can self-assembly into spheres, worm like micelles and wires in THF by varying the length of the PMMA arms,while Star-(PMMA)₆ can form spheres,ellipsoids and wires in THF by adjusting the concentration of star polymer.Star-(PtBMA)₆ can self-assembly into vesicles,spheres and rods in THF by varying the length of the PtBMA arms,while Star-(PtBMA)₆ can form spheres and rods in THF by adjusting the concentration of star polymer.The effects of the length of and properties of polymer arms and the polymer-solvent interaction on the aggregations formed by star polymers were discussed.A series of Star polystyrene-b-poly(N-isopropylacrylamide)(Star-(PS-b-PNIPAAm)₆)with different molecular weight and block ratio were synthesized via the ATRP using bromine -terminated cyclotriphosphazene as initiator.Various morphologies self-assembly from amphiphilic star block copolymers in mixed solvents were obtained by varying solvent,block ration,molecular weight,temperature and so on.Star-(PS₁₈-b-PNIPAAm₇)₆ can self-assembly into rings in CHCl₃/C₂H₅OH,while it can form spheres,giant vesicles and rings in THF/H₂O by adjusting the water content.By varying the block ration and molecular weight, Star-(PS-b-PNIPAAm)can self-assembly various morphologies,Star-(PS₂₄-b-PNIPAAm₂)₆ can from ellipsoids and Star-(PS₁₀-b-PNIPAAm₂)₆ can form giant vesicles in CHCl₃/C₂H₅OH.The effects of the block ratio,solvent,temperature and the polymer-solvent interaction on the aggregations formed by Star-(PS-b-PNIPAAm)were discussed.Star poly methacrylic acid(Star-(PMAA)₆)was obtained after hydrolysis of Star-(PtBMA)₆ in the catalysis of CF₃COOH.The self-assembly behaviors of Star-(PMAA)₆ were studied in H₂O.It was found that Star-(PMAm)₆ could form various morphologies such as vesicles,compound aggregates,pearl-necklace aggregates and cross-linked network in H₂O by varying the molecular weight and concentration of Star-(PMAA)₆.Induced by CTAB,Star-(PMAA)₆ can form nanofibers through the electrostatic assisted assembly,varying the molecular weight of Star-(PMAA)₆ and the ratio of complex units can control the arrangement and aggregation of the fibers.Induced by HDPC,Star-(PMAA)₆ can form rods through the hydrogen bond assisted assembly,varying the molecular weight of Star-(PMAA)₆ and the ratio of complex units can control the length and the diameter of the rods.The self-assembly mechanisms of Star-(PMAA)₆ under different conditions were discussed and possible self-assembly models were proposed.A series of Star poly(2-(dimethyamino)ethyl methacrylate(Star-(PDMAEMA)₆)with different molecular weight and block ratio were synthesized via the ATRP using bromine- terminated cyclotriphosphazene as initiator.Star poly(2-(dimethy ethyl ammonium iodide)ethyl methacrylate (Star-(PDMEAIEMA)₆)was obtained by quaternization of dimethyamino in Star-(PDMAEMA)₆ by ethyl iodide.The self-assembly behaviors of Star-(PDMEAIEMA)₆ in H₂O were investigated. It was found that Star-(PDMEAIEMA)₆ could form various morphologies such as vesicles and honeycomb like aggregates in H₂O by varying the molecular weight of Star-(PDMEAIEMA)₆.By controlling the molecular weight of Star-(PDMEAIEMA)₆ and the ratio of complex units, aggregates with different morphologies and dimensions could be obtained,including fibers and tubes,through the electrostatic assisted assembly of Star-(PDMEAIEMA)₆ induced by SDS. Induced by Star-(PMAA)₆,Star-(PDMEAIEMA)₆ can form various morphologies such as fiber bundles,short fibers,honeycomb like aggregates and spheres in H₂O by adjusting molecular weight,polymer concentration and the ratio of complex units.The self-assembly mechanisms of Star-(PDMEAIEMA)₆ under different conditions were discussed and possible self-assembly models were proposed.