Poly -grafted silica phases

Another interesting approach for the elaboration of ionosilica stationary phases consists in the formation of poly(ionic liquid) (PIL)-grafted silica phases. Poly(l-allylimidazole)-grafted silica appeared as a versatile stationary phase for... 

Figure 14. Schematic model for separation of PAHs by poly(4-vinylpyridine) grafted silica phases in HPLC.

The first successful result was seen in the grafting of poly(octadecyl acrylate) onto silica and its application for separation of PAHs in a reversed phase mode. The polymer is obtained by telomerization of octadecyl acrylate, initiated with 3-mercaptopropyltrimethoxysilane (Fig. 1). The following immobilization is carried out by mixing with porous silica in a suitable solvent. The resultant polymer-grafted silica shows, not only extremely high separation of PAHs, but also specific temperature dependency on the selectivity, which is induced by an ordered-to-disordered transition of the grafted polymer. The detail is described later. 

Poly(methyl acrylate)-grafted silica (Sil-MA, ) showed unexpectedly unique selectivity in a reversed phase mode. The unusual nature of Sil-MA is emphasized by Fig. 2. Octadecylated silica shows a good linearity in the log -log P plots (Fig. 2a), indicating that the elution order is understandable by molecular hydrophobicity of solutes. On the other hand, Sil-MA provides no similar result. As shown in Fig. 2b, it seems to show that Sil-MA , instead, recognizes the molecular size (i.e., the number of the... 

When poly(L-alanine)-grafted silica is applied for separation of PAHs in a reversed phase mode, we can encounter various specific selectivities. For example, 0=10.4 was obtained for a mixture of p- and o-terphenyls, while a= 1.5 in ODS. Both p- and o-terphenyls possess the same numbers in carbon atoms and rr-electrons, but the molecular planarity is entirely different. As indicated in the Corey-Pauling-Koltun (CPK) models of Fig. 7A,p-terphe-nyl is a little twisted (almost planar), but more slender (linear) than o-terphenyl. No similar enhancement of the selectivity is observed in poly(L-leucine)- and poly(L-phenylalanine)-grafted silica. These polypeptides show, rather, similarity to ODS e.g., 0=1.7 in poly(L-leucine)-grafted silica. 

Analytical methods for phospholipid and glycolipid classes by normal-phase high-performance liquid chromatography (HPLC) have been incompletely reviewed. Silica columns with evaporative light scattering detection (ELSD) were mostly used. The poly(vinyl alcohol)-grafted silica column with ELSD could be used to separate them, simultaneously. 

This knowledge encourages us to apply biomimetic membranes for molecular recognition systems such as HPLC. However, lipid membrane systems suffer from a serious problem owing to their instability in organic solvents. To overcome this problem, we have reported the use of poly(octadecyl acrylate)-grafted silica (Sil-ODA ) as a lipid membrane analogue for stationary phases in RP-HPLC. Poly(octadecyl acrylate) cannot... 

Fig. 3 (a) Temperature dependencies of the separation factors of cis- and rran -stilbene with columns Sil-ODA (open circles), Sil-MA (solid circles), and ODS (open triangles). Mobile phase methanohwater (70 30). Sil-MA poly(methyl acrylate)-grafted silica, (b) Schematic illustrations of interaction mechanism between solutes and stationary phases. 

The temperature response of the poly(NIPAAM)-silica matrices depends drastically on the architecture of the grafted polymer molecules. Surface wettability changes dramatically as temperature changes across the range 32-35°C (corresponding to the phase-transition temperature for NIPAAM in aqueous media) for surfaces where poly(NIPAAM) is terminally grafted either directly to the surface or to the looped chain copoljnner of NIPAAM and N-acryloylhydroxysuccinimide which was initially conpled to the surface. The wettability changes for the... 

Introduction of a hydrophobic comonomer, bntyl methacrylate, in the polymer resulted in a decreased transition temperatm-e of ahont 20°C. Retention of steroids in poly(NIPAAM-co-butyl methacrylate)-grafted colnnms increases as colmnn temperature increases. The capacity factors for steroids on the copolymer-modified silica beads was much larger than that on poly(NIPAAM)-grafted columns. The effect of temperature on steroid retention on poly(NIPAAM-co-hntyl methacrylate)-grafted stationary phases was more pronoimced compared to snpports modified with poly(NIPAAM). Furthermore, retention times for steroids increased remarkably as the butyl methacrylate content increased in the copolymer. The temperature-responsive elntion of steroids was strongly affected hy the hydropho-bicity of the grafted polsrmer chains on silica surfaces (63). 

In addition, highly-ordered poly(octadecylacrylate) grafted silica particles prepared in both methods performed eomplete separation for mixtures of various isomeric PAHs polycyclic aromatic hydrocarbons in a methanol-water as a mobile phase as mentioned in many of our previous investigation [59]. Their elution orders are the same as those that can be observed with ODS. It is also showed that the retention factor k) increases with an increase in mobile phase polarity. The performance of Sil-to-ODA and Sil-from-ODA is imique because of its attractive temperature dependencies behavior. As shown in Fig. 7, both Sil-to-... 

Polybetaine-based materials [291] and polybetaines grafted (or adsorbed) onto an inorganic particle surface are applicable as a stationary phase for ion chromatography [292]. The separation capability of poly[3-diethyl(methyl-methacryloylethyl)ammonium propanesulfonate] (polyDMAPS) grafted to silica gel and physically adsorbed onto silica gel was compared with respect... 

---