| As a new type of polymer material,monodisperse polymer microspheres have been widely used in many emerging fields.Siloxane-containing polymers have been extensively studied,because of their interesting properties.Among the diverse siloxane-containing polymers,poly?urea–siloxane??PUS?is of special importance.However,the related studies are all focused on their bulk materials without specific forms,preparation of PUS microspheres is rarely reported.Compared with the traditional methods for thepreparation of polymer microspheres,precipitation polymerization is simple,there is no need for any additives and the surface of the prepared product is clean.In this paper,PUS was prepared through precipitation polymerization of?,?-aminopropy disiloxane?APDS?and toluene diisocyanate?TDI?in H2O-acetone mixed solvent,without extra additions of surfactants,initiators,or any other additives.Effects of monomer ratio?APDS/TDI,m/m?,binary solvent composition?H2O/acetone,m/m?,and reaction temperature on the polymerization process and PUS morphology were investigated.Results indicated that the PUS morphology was readily changed from a porous and irregular form into porous microspheres,by varying simply the APDS/TDI ratio under given experimental conditions.Specifically,the porous and irregular PUS appeared at APDS/TDI ratio below 2/8;while the porous microspheres occurred at APDS/TDI ratio of 3/7 or higher;and porous PUS microspheres,of about 1?m in diameter with narrow polydispersity were obtained with APDS/TDI ratio at 4/6.In addition,the size and size distribution of PUS microspheres were also affected remarkably by H2O/acetone ratio and the polymerization temperature.The narrowest size distribution of 1.04 was realized at APDS/TDI ratio of 4/6,H2O/acetone ratio of 3/7,and at 30°C for the polymerization temperature.With APDS/TDI ratio varied from0/10 to 4/6,the pore volume of PUS materials increased from about 1.79 cm3/g to 2.36 cm3/g,whereas the specific surface area decreased from about 163.00 m2/g to 106.18 m2/g.The changes in PUS morphology and porous properties versus APDS/TDI ratio variation were well interpreted through the mechanisms of polymer precipitation and pore formation.PUS chemical structure was analyzed by FTIR and NMR,while thermal property characterization indicated an enhanced thermal stability with the incorporation of APDS units into polyurea chains.In this paper,fluorescence PUS?FPUS?microspheres without conventional chromophore were also prepared by precipitation polymerization in ternary solvent mixure of acetonitrile/acetone/H2O using isophorone diisocyanate?IPDI?and APDS as the monomers.Effects of monomer ratio?APDS/IPDI,m/m?,ternary solvent composition,and reaction temperature on the polymerization process were investigated.The effect of monomer ratio on the fluorescence characteristics of FPUS was discussed.The preliminary application of FPUS is explored.A narrowest size distribution of 1.005 was realized at APDS/IPDI ratio of 3/7,monomer concentration of 11 wt%,acetonitrile/acetone/H2O ratio of 65/20/15?m/m?,and with polymerization temperature at 30°C.In this system,the microspheres were well formed even when the monomer concentration went up to 20 wt%,with a yield of the FPUS microspheres of 93.91%.Fluorescence tests showed that fluorescence intensity of the solid FPUS increased with the increase in APDS/IPDT,and the mechanism of fluorescence quenching was observed with addition of aqueous solution of metal Cr?VI?.Uniform raspberry-like SiO2@polyurea?SiO2@PU?microspheres with core/shell structure were prepared using isophorone diisocyanate?IPDI?as the sole monomer in H2O/acetone mixture in the presence of commercial SiO2 nanoparticles.The protocol was featured by its simple one-step process under mild conditions?room temperature,90 min?with high sphere yield and complete monomer conversion.Sphere size and surface roughness of SiO2@PU composite microspheres were readily adjustable by changing IPDI loading,SiO2particle size and amount.The content of SiO2 in SiO2@PU composite microspheres gradually increased with the amount of SiO2 added in the polymerization.SiO2 content reached 14.0wt%,22.0 wt%and 28.0 wt%,respectively,when the size of SiO2 nanoparticles was 32 nm,85 nm and 151 nm,respectively.The raspberry-like and core/shell structures were confirmed by SEM and TEM observation with compact PU in the core and multilayer of SiO2 particles on the shell.Formation mechanism of SiO2@PU microspheres was provided based on the solvent-swollen PU surface and the electrostatic interaction between SiO2 nanoparticles and PU polymer.The contact angle of water droplet on the surface of layered SiO2@PU microspheres was 153.5°with a roll-off angle of 3°,revealing the superhydrophobicity of SiO2@PU microspheres.As a preliminary trial for their applications,SiO2@PU microspheres were used for water-oil separation and were demonstrated to have high separation efficiency.This work provides a novel and simple protocol for the preparation of raspberry-like SiO2@PU microspheres with superhydrophobicity. |
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