Preparation of poly(N-isopropylacrylamide) brush grafted silica particles via surface-initiated atom transfer radical polymerization used for aqueous chromatography

Abstract

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-bromoisobutyratefunctionalized silica particles in 2-propanol aqueous solution at ambient temperature using CuCl/CuCl 2 /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/ m 2 and 0.0215 chains/nm 2 , respectively. The gel permeation chromatography (GPC) result showed the relatively narrow molecular weight distribution (M w /M n = 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. Temperaturedependent 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.

Colloidal Probes of PNIPAM-Grafted SiO2 in Studying the Microrheology of Thermally Sensitive Microgel Suspensions

“…In Figure 3(b), for the modified SiO 2 -BIBB, the strong absorption at 1635 cm − 1 attributes to the C�O stretching of BIBB, and those at 1390 cm − 1 and 946 cm − 1 are from the symmetric deformation and wagging vibrations of methyl, indicating that the initiator has been successfully introduced onto the surface of SiO 2 . In Figure 3(c), for SiO 2 -PNIPAM, two bands at 1647 cm − 1 and 1541 cm − 1 are the typical signals of amides, Band I is assigned to the stretching vibration of C�O and Band II to the bending of N-H and stretching of C-N [34,35]. Bands at 1463 cm − 1 and 1398 cm − 1 are assigned to the -CH(CH 3 ) 2 vibrational absorption, and band at 1172 cm − 1 is from the skeletal stretching vibration of C-C in the group of -CH(CH 3 ) 2 .…”

Effect of the grafting ratio of poly(N‐isopropylacrylamide) on thermally responsive polymer brush surfaces

“…The PNIPAAm-grafted silica particles were packed into a stainless steel column (2.1 × 100 mm) and equilibrated with the Milli-Q water [6][7][8]11]. Then the thermally responsive chromatography experiments were performed with an HPLC system consisting of a Shimadzu LC-20AT HPLC instrument with a Shimadzu SPD-20A UV detector setting at 254 nm.…”

“…Stimuli-responsive polymers are sensitive to the change of external conditions, such as temperature, light, pH, magnetic, electric fields, and ionic strength [1][2][3][4][5]. Poly(Nisopropylacrylamide) (PNIPAAm) is a thermoresponsive polymer, which has a lower critical solution temperature (LCST) of 32°C and it exhibits a reversible change of its solubility in response to the changes of temperature [6][7][8][9][10][11]. When the temperature is below its LCST, PNIPAAm is hydrophilic and soluble in water.…”

Fabrication of Phosphate-Imprinted PNIPAM/SiO2 Hybrid Particles and Their Phosphate Binding Property

“…Despite the fact that the physical method is simple, it is easy to lead to fall off of the polymer chains from the silica surface under the complicated condition, for instance, pH change. In the chemical method, polymers can be grown from initiators anchored onto the surface, and core-shell structures with a controllable polymer layer can be chemically formed [ 44 ]. As compared with the physical method, the chemical grafting method provides core-shell structures that are more effective to change the charge and performance of the silica surface, besides having advantages of higher stability and being easier to control.…”