Monolithic preparation

A rather limited range of mesopores in terms of size and volume were observed in the skeletons of polymer monoliths. The porosity of the polymer monolith seems to be lower than that of silica monolith. The total porosity of these monoliths is in the range of 0.61-0.73, whereas interstitial (through-pore) porosity and mesopore porosity are 0.28-0.70 and 0.03-0.24, respectively. In the case of poly(butyl methacrylate-co-ethylene dimethacrylate), the observed porosity is around 0.61-0.71, resulting in permeability 0.15-8.43 x 10 14 m2, whereas the observed porosity of silica monoliths prepared in a capillary is 0.86-0.96 and the permeability is 7-120 x 10 14 m2. Higher permeability will be advantageous for 2D applications, as mentioned later. 

Siouffi, A.M. (2003). Silica gel-based monoliths prepared by the sol-gel method facts and figures J. Chromatogr. A 1000, 801-818. 

Brook, M.A., Chen, Y., Guo, K., Zhang, Z., Jin, W., Deisingh, A., Cruz-Aguado, J. and Brennan, J.D. (2004) Proteins entrapped in silica monoliths prepared from glyceroxysilanes. Journal of Sol-Gel Science and Technology, 31,343-348. 

Fig. 12.11 Transparent star gel monoliths prepared with calcium alkoxide (right) and without calcium (left).

Fig. 2 a - d. Scanning electron micrographs of the inner part of the norborn-2-ene monolith prepared by ring-opening metathesis copolymerization (Reprinted with permission from [58], Copyright 2000 American Chemical Society)... 

The polymerization temperature, through its effects on the kinetics of polymerization, is a particularly effective means of control, allowing the preparation of macroporous polymers with different pore size distributions from a single composition of the polymerization mixture. The effect of the temperature can be readily explained in terms of the nucleation rates, and the shift in pore size distribution induced by changes in the polymerization temperature can be accounted for by the difference in the number of nuclei that result from these changes [61,62]. For example, while the sharp maximum of the pore size distribution profile for monoliths prepared at a temperature of 70 °C is close to 1000 nm, a very broad pore size distribution curve spanning from 10 to 1000 nm with no distinct maximum is typical for monolith prepared from the same mixture at 130°C [63]. 

Living free-radical polymerization has recently attracted considerable attention since it enables the preparation of polymers with well-controlled composition and molecular architecture previously the exclusive domain of ionic polymerizations, using very robust conditions akin to those of a simple radical polymerization [77 - 86]. In one of the implementations, the grafting is achieved by employing the terminal nitroxide moieties of a monolith prepared in the presence of a stable free radical such as 2,2,5,5-tetramethyl-l-pyperidinyloxy (TEMPO). In this way, the monolith is prepared first and its dormant free-... 

FIGURE 8.6 SEM of an organo-silica hybrid monolith prepared with the precursor A-octadecyldimethyl[3-(trimethoxysilyl)propyl] ammonium chloride to provide reversed phase stationary phase and anodic EOF. (a) Cross-sectional view (magnification 1800 times) and (b) longitudinal view (magnification 7000 times). (Reprinted from J. D. Hayes, A. Malik, Anal. Chem., 72 4090 (2000). With permission. Copyright American Chemical Society 2000.)... 

FIGURE 8.8 (a) SEM image of organo-silica monolith prepared with the APTES and TEOS ... 

FIGURES.13 SEM images of macroporous methylorgano-silica monoliths prepared in capillaries with various inner diameters. (Adapted from K. Nakanishi, Bull. Chem. Soc. Jpn., 79 673 (2006). With permission. Copyright The Chemical Society of Japan 2006 M. Motokawa et al., J. Chromatogr. A, 961 53 (2002). Copyright Elsevier 1992.)... 

Monoliths Prepared by Porogen Alteration and Surface Alkylation.84... 

Due to their specific molecular recognition properties, MIPs have found their main application in analytical chemistry. As outlined in the introduction, the common preparation method of MIPs as bulk polymers, which are subsequently crushed, ground and sieved to obtain particles, is not well adapted to achieve a high separation performance. Thus, the preparation of monolithic MIPs seemed particularly attractive for separation science due to the permeability properties, the easy in situ preparation and the absence of retaining frits. On the other hand, the use of the monolith format is still limited and the strategy of MIP monolith preparation has been little developed in recent years. 

The fabrication of imprinted monolithic solid-phase microextraction fibres has been developed for the selective extraction and preconcentration of diacetylmorphine and its structural analogues, triazines, bisphenol A, anaesthetics, and antibiotics followed by GC or HPLC analysis [156,163,179,196,197]. In addition, the on-line coupling of the imprinted monolith as a preconcentration column with a conventional analytical column has been proposed for the enrichment and cleanup of environmental and food samples [163]. However, at present, the capacity of the imprinted fibres and thus the degree of recovery of analytes are very variable and obviously need some improvement. For example, the recoveries of triazines after SPME with an imprinted monolith prepared by in situ polymerisation of MAA as... 

Figure 2.66 Preparation of a ceramic monolith to obtain a cross-flow heat exchanger (left) and different options of monolith preparation (right) [102].

The ratio between the through-pore size (ca. 8 pm) and the skeleton size (ca. 2.2 pm) shown in Fig. 5.2a is much greater than in a packed bed of a particle-filled column. Figure 5.3 shows the plots of skeleton size against the through-pore size in a column for a silica monolith prepared in a capillary or in a mould, as well as in a particle-packed column. The through-pore size/skeleton size ratios observed with the... 

Fig. 6.29. Electrochromatographic performance of monoliths prepared by copolymerization of ethylene dimethacrylate and chiral monomer 25 with glycidyl methacrylate (a) and 2-hydroxyethyl methacrylate (b) as comonomers. (Reprinted with permission from [60]. Copyright 2000 American Chemical Society). Conditions capillary column 335 mm (250 mm active length) x 0.1 mm i.d., pore size 993 nm (a) and 1163 nm (b), analyte DNB-(R,S)-leucine, mobile phase 400 mM acetic acid and 4 mM triethylamine in acetonitrile-methanol (80 20, v/v), 25 kV, temperature 30°C.

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