Preparation And Characterization Of Brush-Shaped Copolymers Via Combined Living Anionic Polymerization And Ring-Opening Metathesis Polymerization

Brush-shaped polymer is defined as a kind of graft polymer in which various side polymer chains are linked onto one linear polymer backbone with equal spacing.Compared to the corresponding linear analogues,brush-shaped polymers have some unique physicochemical properties,such as small hydrodynamic diameter,low solution and melt viscosity,low crystallinity and low glass transition temperature.In addition,if the chemical composition of side chain is different from main chain,the brush-shaped polymers will undergo phase separation and self-assemble into unique supramolecular nanostructures.Three methodologies are usually used for synthesizing brush-shaped polymers,including "grafting through","grafting onto" and "grafting from" strategies.In this thesis,a "grafting through" strategy combining living anionic polymerization(LAP)and ring-opening metathesis polymerization(ROMP)was used to prepare two types of brush-shaped copolymers,and their chemical structures were systematically studied.In details,the main research contents are as follows:(1)Synthesis and characterization of brush-shaped copolymers based on polystyrene(PS)and polyisoprene(PI)Firstly,the hydroxyl-terminated polymers PS-OH and PI-OH were respectively synthesized by living anionic polymerization,two norbornene-capped macromonomers PS-Nor and PI-Nor were then synthesized by esterification reaction with exo-5-norbornene-2-carboxylic acid.Finally,by changing the feeding ratios and feeding sequences in ring-opening metathesis polymerization,we have synthesized the block-type brush-shaped copolymers P(PS)-b-P(PI)and P(PS)-b-P(PI)-b-P(PS),as well as the random-type brush-shaped copolymers P(PS)-co-P(PI)with different proportions and arrangement sequences of side polymer chains.The chemical structure,molecular weights and dispersities(D)of copolymers were characterized by nuclear magnetic resonance spectroscopy(1H-NMR,13C-NMR),Fourier transform infrared(FT-IR)and gel permeation chromatography(GPC).The glass transition temperature(Tg)and thermal decomposition temperature were measured by differential scanning calorimetry(DSC)and thermal gravimetric analysis(TGA).This method provides a simple and efficient way to synthesize brush-shaped polymers.(2)Synthesis and characterization of amphiphilic brush-shaped copolymers based on polystyrene and poly(ethylene glycol)(PEG)The norbornene-capped macromonomers PS-Nor and PEG-Nor with similar molecular weights were first prepared via esterification reaction between exo-5-norbornene-2-carboxylic acid and PS-OH or monomethoxyl poly(ethylene glycol).Subsequently,ROMP reaction was used to synthesize block-type brush-shaped copolymers P(PS)-b-P(PEG)and random-type brush-shaped copolymers P(PS)-co-P(PEG)with different proportions and arrangement sequences of side polymer chains.The chemical structures were characterized by nuclear magnetic resonance spectroscopy(1H-NMR,13C-NMR),Fourier transform infrared(FT-IR),matrix-assisted laser desorption/ionization time-of-flight(MALDI-TOF)mass spectroscopy and gel permeation chromatography(GPC).The thermal decomposition temperature and glass transition temperature(Tg)of the polymers were also studied by TGA and DSC.In summary,we have designed and synthesized two types of brush-shaped copolymers with different chemical compositions and arrangement sequences of side chains,investigating their chemical structures and themal properties.This study enriches the synthesis methodology of well-defined brush-shaped polymers.