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Ion-exchangers, adsorbents, supported catalysts, etc, derived from porous copolymer beads are employed as medium in fine chemical separation processes. In these processes the exchange of reagents completes earlier in the smaller beads than in the larger beads in the same lot, which reduces the separation efficiency. So, it is potentially advantageous to preferentially introduce the macropores in the larger beads, as the macropores provide fast access to the reagents into the inner portions of the beads. In this study, camphor-a sublimable organic compound was employed as a diluent to create porosity in 4-vinylpyridinedivinylbenzene copolymer beads produced by o/w suspension polymerization technique. Camphor preferentially introduced macropores in the larger beads in the reaction. The results are explained on the basis of removal of diluent by sublimation phenomenon from the polymerizing droplets at a faster rate from the smaller beads as compared to the larger beads in the same batch.

A new mass spectrometric method is proposed for measurement of 234U/238U ratio with a single Daly electron multiplier detector using the general peak jump method. The method is based on precise measurement of the 235U/238U ratio and 234U/235U ratio, which are used to calculate the 234U/238U ratio using the equation 234U/238U = 235U/238U x 234U/235U. The results show a significant improvement, i.e., more than 35 times better precision in measuring the (234)U/(238)U ratio with this method (sigma = 2.9 x 10(-8)) as compared to direct measurement of 234U/238U (sigma = 1.1 x 10(-6)). The method widens the applicability of the single collector system, and it will potentially be helpful to improve the precision in the case of the static multicollector system also.

ABSTRACT:A series of porous copolymer beads were synthesized by suspension copolymerization of 4-vinylpyridine (4VP) with ethylene glycol dimethacrylate (EGDM) in the presence of diluents, cyclohexanone (CHN), and toluene (TOL). The resulting copolymer beads were characterized for their density, porosity, surface area, mechanical strength, and c1-ion capacity. It was observed that the apparent density of the copolymer beads decreases with the decrease in CHN of a given mixture of diluents, % cross-linking agent (EGDM) and with the increase in solvent fraction (F,). It was also observed that the porosity and surface area of the copolymer beads increase with the decrease in CHN of a given mixture of diluents, % cross-linking agent and with the increase in solvent fraction. The mechanical strength of the copolymer beads decreases with the increase in solvent fraction. The c1-ions capacity of the copolymer beads decreases with the increase in % cross-linking agent whereas it is almost independent of the change of one component of a given mixture of diluents and solvent fraction.KEY WORDS 4-Vinylpyridine-Ethylene Glycol Dimethacrylate Copolymers / Porous Structure / Diluents / Solvent Fraction/ Suspension Polymerization/ Porosity/ Surface Area/ Mechanical Strength/ Copolymer Beads / Pore Size Distribution Curve / It has been reported in the literaturel.2 that anionexchange resin of hydrophilic nature can be synthesized by the copolymerization of 4-vinylpyridine with ethylene glycol dimethacrylate. Such hydrophilic resins have been used with certain advantages over the hydrophobic resins (4-vinylpyridine-divinylbenzene) for the separation of proteins particularly the serum albumin components.Sugii et al. 1 pointed out that although 4VP-divinylbenzene (DVB) has a larger pore diameter (27.5 nm pore radius) than 4VP-EGDM (8.7nm pore radius) in the dry state, the exclusion limits of both resins were similar ( 500 daltons) and small. These results have been explained on the basis of their findings that the pore volumes of the resins in the wet state were 0.38 ml ml -i of 4VP-DVB and 0.34 ml ml-1 of 4VP-EGDM, i.e., nearly identical, indicating that the pore size distribution of both resins in the wet state is different from that in the dry state. Therefore, the 4VP-EGDM resin having a hydrophilic cross-linking structure is relatively more suitable anion-exchanger for the separation of proteins.It has also been reported that the pore size of the resin markedly affects the resolution and recovery of proteins in reversed-phase chromatography 3 • 4 and in ion-exchange chromatography. 5 -7 Ion exchange chromatography has the advantage that it can be carried out in an aqueous solution rather than in an organic solvent. Therefore, it is possible to prevent the denaturation of proteins caused by organic solvents. In the separation of proteins the use of ion-exchange resins of organic polymer matrix 2 • 8 -10 have certain advantages over surfacemodified silica gels such as chemical stability in alkaline solution, higher sample loa...