Preparation And Properties Of Core-shell Polymer Brushes

Organic-inorganic nanocomposites composed of polymers and nanoparticles offer a vast design space of potential material properties,depending heavily on the properties of these two constituents and their spatial arrangement.In this work,firstly,silica nanoparticles were synthesized,surface atom transfer radical(ATRP)synthesis was then used to graft monomers that is either thermo-responsive or pH-responsive onto the surface of silica nanoparticles to fabricate core-shell polymer brushes.Moreover,physical properties of the core-shell polymer brushes were investigated.This work includes the following two parts:1.Synthesis and characterization of core-shell polymer brushesSilica nanoparticles were synthesized by the Stober method and followed with modification by 3-aminopropyltrimethoxysilane(APTMS)and 2-bromoisobutyryl bromide(BiBB)to synthesize spherical particle initiator,SiO2-Br.Atom transfer radical polymerization(ATRP)was employed to graft oligoethylene glycol methyl ether methacrylate(OEGMA)or/and tert-butyl acrylate(tBA)monomers onto the surface of silica nanoparticles initiator to fabricate core-shell polymer brushes.By this synthesis procedure,we prepared SiO2-g-POEGMA,SiO2-g-PtBA and SiO2-g-P(OEGMA-stat-tBA)core-shell polymer brushes.SiO2-g-PtBA and SiO2-g-P(OEGMA-stat-tBA)were then hydrolyzed to get SiO2-g-PAA and SiO2-g-P(OEGMA-stat-AA),respectively.Fourier transform infrared spectra(FT-IR),thermogravimetric analysis(TGA),transmission electron microscopy(TEM),gel permeation chromatography(GPC),1H NMR spectra and dynamic light scattering(DLS)were used to characterize the core-shell polymer brushes.2.Physical properties of core-shell polymer brushesThe particle size of core-shell polymer brushes,SiO2-g-POEGMA,SiO2-g-PAA and SiO2-g-P(OEGMA-stat-AA),were measured by dynamic light scattering under different temperature and pH.The results indicate that the lower critical solution temperature(LCST)of SiO2-g-POEGMA is 63? and the size of the particle decreases with increased temperature above the LCST.For SiO2-g-PAA,the particles size increases with increased pH due to the surface potential becomes more negative with higher pH.Notably,we synthesized SiO2-g-P(OEGMA-stat-AA)with various content of AA in the polymer brushes,including SiO-g-P(OEGMA30-stat-AA70),SiO2-g-P(OEGMA50-stat-AA50)and SiO2-g-P(OEGMA70-stat-tBA30).The LCST of the SiO2-g-P(OEGmA-stat-AA)were determined by DLS under different pH and temperature.The LCST of SiO2-g-P(OEGMA30-stat-AA70),SiO2-g-P(OEGMA50-stat-AA50),SiO2-g-P(OEGMA70-stat-AA30)is 57?,66?,71?,respectively.This result indicates that the LCST increases with increasing percentage of OEGMA in the polymer brushes,broadening of the responsive temperature range of the core-shell polymer brushes.Pickering emulsion was prepared with SiO2-g-POEGMA as stabilizer and oil-water ratio as 2:1.The emulsion did not take phase separation and demulsification during the 15 day,indicating that the Pickering emulsion prepared by the experiment had good stability.