Synthesis And Application Of Spherical Polyelectrolyte Brushes Grafting On Poly(Butadiene) Nano-particles

In this paper, new spherical polyelectrolyte brushes consisted of a poly(butadiene) (PB) latex with diameter of 320 nm as core and chemically grafted linear poly (acrylic acid) (PAA) chains as shell were synthesized by photoemulsion polymerization and conventional emulsion polymerization respectively. The length and grafting density of PAA chains could be controlled. We studied the catalytic activity of nickel nanoparticles prepared and immobilized in spherical polyelectrolyte brushes acting as nano-reactors.(1) SPB prepared by photo-emulsion polymerization (photo-brushes). The poly (butadiene) (PB) latex particles were coated by a thin layer of photoinitiator HMEM firstly. Then the polymerization of acrylic acid (AA) was initiated by radiation of UV light and PAA brushes were produced on the surface of PB particles. The linear PAA chains can be 0 to 220 nm by controlling the AA monomer content. The pH and ionic strength are the most important factors to affect the size of SPB, which can be determined by dynamic light scattering. The ester bond of the photoinitiator HMEM was cleaved by a strong aqueous base, so the PAA chains were removed from the surface of the particles and analyzed separately. Thus, we obtained the grafting density of PAA brushes.(2) SPB prepared by thermal-emulsion polymerization (thermal-brushes). Adding K2S2O4(KPS) into PB latex, radicals were produced on the surface of PB particles at 80℃, which initiate the polymerization of AA. The PAA chains grafted from the surface of PB particles. The length of PAA chains can be controlled by the concentration of AA monomer. The stretching of PAA chains were affected by pH and ionic strength remarkably like photo-brushes. The improved Daoud-Cotton model was applied to estimate the grafting density of thermal-brushes, which was found to be higher than that of photo-brushes.(3) Adding NiCl4 to photo-brush and thermal-brush latex respectively, the Ni4+ ions concentrated in polyelectrolyte brushes layer. Then Ni4+ was reduced to metallic Ni by added NaBH4, and Ni-brushes nanocomposite particles with catalytic activity were prepared. The application of Ni-brushes nanoparticles to p-nitrophenol reduction in water solution shows that both Ni-photo-brushes and Ni-thermal-brushes have catalytic activity in this reaction. And the former have a higher catalytic activity than the later.