Functional polymers, porous silica

Octadecylsilane (ODS) This is a polymer-coated silica packing with increased loadability of a porous silica support. Nonpolar compounds may be separated using the hydrophobic functionalities offered on ODS. 

Carlier32,33 used various functional alkylsilane groups on silica as co-monomer, transfer agent or initiator for grafting of a functional polymer. These functional polymers may be used to anchor a catalyst. The polymer polyphenylsilsesquioxane was grafted onto porous silica and sulfonated, to obtain catalysts of high stability with enhanced site accessibility and increased number of sites, as well as high acidity level.34 This catalyst is used for esterification and phenol alkylation. Other catalysts have been reviewed by Pinnavaia,35 and are summarized in table 8.5. 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

Adsorption chromatography exploits differences in the relative affinity of solutes for a solid adsorbent used as the stationary phase. Common stationary phase materials for adsorption chromatography are porous silica gel, activated alumina, activated carbon, magnesium oxide, carbonates, and highly cross-linked polymers such as styrene-divinylbenzene and methac-rylates. The chemical natures of these adsorbent stationary phase materials make them well suited for separations of solute mixtures that differ in polarity and chemical functionality. For example, silica is an acidic adsorbent that retains basic compounds to a greater extent than nonbasic ones. In contrast, alumina... 

Several SP materials have been used for the extraction of FRs from aqueous samples, plasma and milk (Table 31.7). Similar materials have been used for all FRs. Typical SP materials include Ci8 and Cg bonded to porous silica, highly cross-linked poly(styrene divinylbenzene) (PS-DVB), and graphitized carbon black (GCB). It is also possible to use XAD-2 resin for extraction of various FRs, pesticides, and plastic additives from large volumes of water (100 1). The analytes can then be either eluted from the resin by acetone hexane mixture, or Soxhlet extracted with acetone and hexane. For a specific determination of diphenyl phosphate in water and urine, molecularly imprinted polymers have been used in the solid phase extraction. The imprinted polymer was prepared using 2-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as the cross linker, and a structural analog of the analyte as the template molecule. Elution was done with methanol triethylamine as solvent. Also solid phase microextraction (SPME) has been applied in the analysis of PBDEs in water samples. The extraction has been done from a headspace of a heated water sample (100°C) using polydimethylsiloxane (PDMS) or polyacryl (PA) as the fiber material. ... 

Porous silica supports such as MCM-41 have also been employed in the development of artificial hybrid pores due to their well-defined porous network and then-facile functionalization chemistry. For instance, Lopez and coworkers employed an MCM-41 support coated uniformly with a temperature-responsive poly(AI-isopropyl acrylamide) (PNIPAAm) polymer. At low temperatures, the polymer was hydrated and extended and the pores were closed no transport of fluorescein was observed when flow cytometry and confocal laser scanning microscopy were employed. In contrast, at high temperatures the polymer was hydrophobic and collapsed, allowing the transport of the dye (Figure 24). This system thus not only acts as a temperature sensor but also shows clear features of control as will become more important in the next section. 

Even very simple polymers without an obvious functionality can have an influence on a mineralization process, as demonstrated for the generation of porous silica in the presence of PEG [255]. PEG had a multiple role serving as flocculation agent in silica sols, silica polymerization agent, phase separation agent, and porogen to generate pore dimensions of 2-20 nm. 

The present study is concerned with the modification of functional polymers onto porous silica particle surfaces. Our primary interest is to improve particle surface characteristics. Poly(acrylic acid) was chosen as the functional polymer to provide pH-intelligent, surface-responsive particles. The PAA chains under acid conditions are usually coiled, while under basic conditions the chains are extended due to electrostatic repulsion of the carboxylate ions. By controlling the pH, the surface characteristics can be tailored to respond to specific pH environments. Pore size distribution and specific surface area of modified silica are calculated from the amount of nitrogen adsorbed on the surface. The water penetration rate and porosity for different pH were measured for estimation of the surface properties ... 

We presented a novel quenched solid non-local density functional (QSNLDFT) model, which provides a r istic description of adsorption on amorphous surfaces without resorting to computationally expensive two- or three-dimensional DFT formulations. The main idea is to consider solid as a quenched component of the solid-fluid mixture rather than a source of the external potential. The QSNLDFT extends the quenched-annealed DFT proposed recently by M. Schmidt and cowoikers [23,24] for systems with hard core interactions to porous solids with attractive interactions. We presented several examples of calculated adsorption isotherms on amorphous and microporous solids, which are in qualitative agreement with experimental measurements on typical polymer-templated silica materials like SBA-15, FDU-1 and oftiers. Introduction of the solid density distribution in QSNLDFT eliminates strong layering of the fluid near the walls that was a characteristic feature of NLDFT models with smoodi pore walls. As the result, QSNLDFT predicts smooth isotherms in the region of polymolecular adsorption. The main advantage of the proposed approach is that QSNLDFT retains one-dimensional solid and fluid density distributions, and thus, provides computational efficiency and accuracy similar to conventional NLDFT models. 

---