Resins pore diameter

Table 12 shows the molecular size of some biological macromolecules for comparison to the mean pore size of the resins. When selecting the pore size of a resin for the recovery or immobilization of a specific protein, a general rule is that the optimum resin pore diameter should be about 4 to 5 times the length of the major axis of the protein. Increasing the pore size of the resin beyond that point will result in decreases in the amount of protein adsorbed because the surface area available for adsorption is being decreased as the pore size is increased. An example ofthis optimal adsorption of glucose oxidase, as defined by enzyme activity, is shown in Fig. Enzyme... 

Figure 16. Effect of resin pore diameter on the enzyme activity of glucose oxidase.

Figure 3 illustrates that the polymerization rate is independent of resin diameter. During 30 min reactions, CALB immobilized on resins 1 to 4 gives turnover frequency (TOF) of e-CL of about 12 s" In contrast, our previous work of CALB immobilized on PMMA resins showed a large dependence of e-CL %-conversion on resin particle diameter. For example, in 30 minutes reaction time, as the particle size decreased from 560-710, 120, 75 and 35 pm, turnover frequency (TOF) of e-CL increased from 3.8 to 5.3, 7.5 and 11.2, respectively. However, by increasing the resin pore size from 300 (resin 4) to 1000 A (resin 5) for 35 pm beads, the TOF reached 28.2 s. As discussed above, increase in resin pore diameter also corresponds to an increase in %-area of beads at which CALB is found (37 to 88%). 

Polymer-based, synthetic ion-exchangers known as resins are available commercially in gel type or truly porous forms. Gel-type resins are not porous in the usual sense of the word, since their structure depends upon swelhng in the solvent in which they are immersed. Removal of the solvent usually results in a collapse of the three-dimensional structure, and no significant surface area or pore diameter can be defined by the ordinaiy techniques available for truly porous materials. In their swollen state, gel-type resins approximate a true molecular-scale solution. Thus, we can identify an internal porosity p only in terms of the equilibrium uptake of water or other liquid. When crosslinked polymers are used as the support matrix, the internal porosity so defined varies in inverse proportion to the degree of crosslinkiug, with swelhng and therefore porosity typically being more... 

Type Composition Character Average Pore Diameter (nm) Specific Specific Solvent Surface Pore Uptake Area Volurc. (g/g) of ( /g) (Ml/g) resin ... 

Figure 28a shows the result of SAXS on sample BrlOOO. We used Guinier s formula (see eq. 6) for the small angle scattering intensity, I(k), from randomly located voids with radius of gyration, Rg. Although Guinier s equation assumes a random distribution of pores with a homogeneous pore size, it fits our experimental data well. The slope of the solid line in Fig. 28b gives R - 5.5 A and this value has been used for the calculated curve in Fig. 28a. This suggests a relatively narrow pore-size distribution with an equivalent spherical pore diameter of about 14A. Similar results were found for the other heated resin samples, except that the mean pore diameter changed from about 12 A for samples made at 700°C to about 15 A for samples made at 1100°C.

In a GPC experiment, the polymer is separated in a column which is filled with a swollen, uniformly packed resin ( gel , called stationary phase, while the solvent which passes through the column is called mobile phase). The gel beads are usually made of crosslinked polymers (in particular polystyrene but also various inorganic porous materials) with little holes and pores of different size where the pore diameter is of the dimension of the size of the solvated polymer coils, i.e., the pore-size distribution is approx. 10-10 nm. 

Re Reynolds number based on the pore diameter Sj Resin-solid interfacial surface within the representative volume... 

XAD-2 resin is a styrene-divinylbenzene copolymer that has a highly aromatic structure. It has a surface area of about 300 m2/g, an average pore diameter of 90 A, and a maximum pore diameter of 290 A. XAD-8 resin is a methyl methacrylate copolymer and has a slightly more hydrophilic surface than XAD-2. It has a surface area of about 140 m2/g, an average pore diameter of 250 A, and a maximum pore diameter of 375-840 A. Each exhibits different adsorption characteristics because of structural and surface chemistry differences. Both XAD resins have a significant number of micropores <25 A in diameter. The adsorption area is distributed biomodally in XAD-8 and has maximums at 22.5 A or less and at 375 A. XAD-2 has a maximum at 22.5 A or less and a slight increase at 240 A (11). This result indicates that XAD-2 adsorption is initially more diffusion-limited than XAD-8. 

An additional consideration in the cleaning of XAD resins is their flexible structure. The resin beads swell on contact with hydrophilic or polar solvents such as methanol (29). The nonpolar surface of the resin is repelled by polar solvents and attracted by nonpolar solvents. This effect causes the internal pore diameters to increase or decrease, respectively. The cleaning solvent or mixture of solvents must be polar to keep the internal pores open so that the contaminants will diffuse faster from the interior of the beads to the bulk solvent. However, the resin contaminants themselves are nonpolar, as shown in Table IV, and are not very soluble in polar solvents. The choice of an optimum resincleaning solvent should therefore be a compromise between diffusion and solubility. In addition, the solvent used after the water backwash must be miscible with water to remove the water from the resin pores. 

Such a process was attempted by treating the elastin from ligamentum nuchae first with several successive additions of pancreatic elastase and then further degrading the product with papain imtil all but a few per cent of the product was dialyzable through cellophane. The diffusate was then treated, in series, with a range of ion-exchange resins with varying internal pore diameter. The resins were of the suKonated polystyrene type, in bead form, and had nominal divinylbenzene (DVB) contents of 2 %, %,... 

Ag and Co functionalized adsorbents for the PPhs adsorption. These transition-metal functionalized adsorbents were prepared by immobilizing Ag and Co onto a solid carrier, for which Amberlyst IS has been selected. Amberlyst 15, a macroreticular polystyrene - crosslinked by divinylbenzene - sulfonated cation exchange resin, has been selected as carrier because of its large pore diameter of approximately 100 [nm]. These macropores ensure the accessibility for the relatively large PPh3 ligands. 

Carbon molecular sieve membranes. Molecular sieve carbons can be produced by controlled pyrolysis of selected polymers as mentioned in 3.2.7 Pyrolysis. Carbon molecular sieves with a mean pore diameter from 025 to 1 nm are known to have high separation selectivities for molecules differing by as little as 0.02 nm in critical dimensions. Besides the separation properties, these amorphous materials with more or less regular pore structures may also provide catalytic properties. Carbon molecular sieve membranes in sheet and hollow fiber (with a fiber outer diameter of 5 pm to 1 mm) forms can be derived from cellulose and its derivatives, certain acrylics, peach-tar mesophase or certain thermosetting polymers such as phenolic resins and oxidized polyacrylonitrile by pyrolysis in an inert atmosphere [Koresh and Soffer, 1983 Soffer et al., 1987 Murphy, 1988]. 

Such a structure is termed macroporous with a typical average pore diameter of about 150 nm and a pore size range from several tens to several hundred nanometres. By comparison a gel resin is characterized by an apparent porosity of no greater than about 4 nm which represents the average distance of separation of polymer chains. This difference in structural characteristics of gel and macroporous resins is clearly evident when comparing Figures 3.2a and 3.2b. 

Resin Composition" Average Pore Diameter A Specific Surface Area (m /g)" Specific Pore Volume (crnVg)" Solvent Uptake, g per g of Dry Resin ... 

The resin substrate studied most often in anion chromatography is XAD-1. The substrate has the lowest surface area (100 m /g) and the largest average pore diameter (205 A) of the XAD series. The physical stability is excellent. XAD-1 can be converted to an anion exchanger very easily by chloromethylation, followed by amination with a tertiary amine. 

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