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Frontiers of Materials Science

Front Mater Sci    2012, Vol. 6 Issue (1) : 60-68     DOI: 10.1007/s11706-012-0161-9
Preparation of poly(N-isopropylacrylamide) brush grafted silica particles via surface-initiated atom transfer radical polymerization used for aqueous chromatography
Zong-Jian LIU1, Yan-Li LIANG1, Fang-Fang GENG1, Fang LV1, Rong-Ji DAI1(), Yu-Kui ZHANG1,2, Yu-Lin DENG1()
1. School of Life Science, Beijing Institute of Technology, Beijing 100081, China; 2. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes were densely grafted onto silica surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The grafting reaction started from the surfaces of 2-bromoisobutyrate-functionalized silica particles in 2-propanol aqueous solution at ambient temperature using CuCl/CuCl2/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as the catalytic system. Based on thermogravimetric analysis (TGA) results, the grafting amount and grafting density of PNIPAM chains on the surface of silica were calculated to be 1.29 mg/m2 and 0.0215 chains/nm2, respectively. The gel permeation chromatography (GPC) result showed the relatively narrow molecular weight distribution (Mw/Mn=1.21) of the grafted PNIPAAm. The modified silica particles were applied as high-performance liquid chromatography (HPLC) packing materials to successfully separate three aromatic compounds using water as mobile phase by changing column temperature. Temperature-dependent hydrophilic/hydrophobic property alteration of PNIPAAm brushes grafted on silica particles was determined with chromatographic interaction between stationary phase and analytes. Retention time was prolonged and resolution was improved with increasing temperature. Baseline separation with high resolution at relatively low temperatures was observed, demonstrating dense PNIPAAm brushes were grafted on silica surfaces.

Keywords poly(N-isopropylacrylamide) (PNIPAAm)      atom transfer radical polymerization (ATRP)      temperature-responsive chromatography      separation     
Corresponding Authors: DAI Rong-Ji, (R.J.D.); DENG Yu-Lin, (Y.L.D.)   
Issue Date: 05 March 2012
 Cite this article:   
Zong-Jian LIU,Yan-Li LIANG,Fang-Fang GENG, et al. Preparation of poly(N-isopropylacrylamide) brush grafted silica particles via surface-initiated atom transfer radical polymerization used for aqueous chromatography[J]. Front Mater Sci, 2012, 6(1): 60-68.
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Zong-Jian LIU
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Fig.1  Preparation of PNIPAAm grafted silica surface via surface-initiated atom transfer radical polymerization (SI-ATRP).
Fig.2  FT-IR spectra of 3-aminopropyl silica (a), 2-bromoisobutyrate-functionalized silica (b), and PNIPAAm grafted silica (c).
Fig.3  TGA curves of 3-aminopropyl silica (a), 2-bromoisobutyrate-functionalized silica (b), and PNIPAAm grafted silica (c).
Fig.4  GPC of the PNIPAAm grafted on silica surfaces. The PNIPAAm brushes were cleaved from silica particles via etching with hydrofluoric acid.
CodeElemental composition /%a)mp/(mg·m-2)Mnb)MW/Mnb)Grafting density /(chains·nm-2)
3-aminopropyl silica0.762.520.73
2-bromoisobutyrate-functionalized silica0.673.850.86
PNIPAAm-grafted silica3.6218.543.421.2936,2001.210.0215
Tab.1  Characterization of silica particles
Fig.5  DSC curves of 2-bromoisobutyrate-functionalized silica (a) and PNIPAAm grafted silica (b).
Fig.6  Chromatogram of aromatic compounds on PNIPAAm grafted silica packed column at various temperatures. Mobile phase, water; flow rate, 0.3 mL/min. Detection wavelength: 254 nm. Peaks: 1, toluene; 2, diphenyl ketone; 3, biphenyl.
Fig.7  Temperature dependency of the retention time on PNIPAAm grafted silica packed column: biphenyl (a); diphenyl ketone (b); toluene (c).
Fig.8  The van’t Hoff plots of aromatic compounds on the PNIPAAm grafted silica column with water as the mobile phase: biphenyl (a); diphenyl ketone (b); toluene (c).
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