Preparation and Characterization of Temperature‐responsive Porous Monoliths

Abstract

A new temperature-responsive porous monolith has been prepared by surface-initiated activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) grafting poly(N-isopropylacrylamide) (PNIPAAm) within the pores of the porous polymer monolith. The grafting copolymerization was carried out by a method based on a continuous flow-through technique without special deoxygenation procedure needed in the general ATRP. The addition of ascorbic acid could counteract the oxidation effect of oxygen diffusing into the reaction system. The resulting grafted monolith was characterized by a mercury intrusion method and the size of macropore was 3.65 µm, which was suitable for flow through the monolith for HPLC. The thermally responsive property of the grafted monolith was evaluated by HPLC using steroids with various hydrophobicities as probes. Through determination of retention factor of each steroid on the grafted monolith at different temperatures using water as mobile phase, it was found that the slope of the plot of retention factor of each steroid versus the temperature changed around the low critical solution temperature (LCST, 32 ℃) of PNIPAAm in water. It was relative to the grafted PNIPAAm temperature sensitivity that a hydrophobic and hydrophilic alternation would take place around its LCST. Based on this thermally responsive property, the grafted monolith was used as stationary phase for HPLC and to separate the steroids using water as mobile phase by changing the column temperature. As a mobile phase, water is much better than organic solvents concerning the environment.

Porphyrins and phthalocyanines in solar photovoltaic cells

“…Work to replace the liquid electrolyte with a solid hole-transport medium has been undertaken by several research groups. One of the first porphyrin-based solidstate DSSCs was reported by Zhang and Xiao in 2000 [154]. The device was made up in the following order: SnO 2 /TiO 2 /TCPP/CuI/Al with CuI acting as the solid hole transporter.…”

Separation of peptides with an aqueous mobile phase by temperature‐responsive chromatographic column

“…The retention times were prolonged, and the resolution was improved with increasing temperature. Prior reports by us and by others demonstrated that the PNIPAAm grafted silica exhibited hydrophilic property at lower temperatures than LCST, while the surfaces were hydrophobic at higher temperatures . As a result, the weak interaction between peptides and hydrophilic PNIPAAm resulted in poor separation at 10°C, whereas the enhanced hydrophobic interaction became the primary separating force at 50°C.…”

“…The surface property and function of the stationary phase is modulated by external temperature to fulfill separation requirements without changing mobile phase composition. In addition to particle‐packed column, PNIPAAm was also used to prepare thermoresponsive monolithic column on which proteins , steroids , and aromatic ketones , were well resolved with a short analysis time and relatively high column efficiency. Thermally driven separation of benzoic acid and nicotinic acid using a PNIPAAm‐grafted capillary column in electrochromatography was reported previously by our group .…”

“…One of its main disadvantages is the relatively low grafting density. The “grafting from” approach can produce high grafting density surfaces with good control of molecular weight . However, prior studies reported that dense, high molecular weight PNIPAAm brushes allowed for the penetration of analytes into polymer chains, leading to broad peak and unfavorable resolution .…”

Source Discrimination of Heavy Metals in the Inland River Sediment in Suzhou City, Anhui Province: Multivariate Statistical Approaches

“…Due to their insolubleness in water, most of heavy metal pollutants will bind to the sediment and suspended solids which mostly transfer to the sediment. So the distribution of heavy metals in the sediment can reflect the pollution condition of river basin [11]. In a word, it is essential and valuable to research heavy metals of sediment in the river for the river pollution analysis.…”