Steinar Hagen

Monosized stationary phases for chromatography

Abstract Polymer particles with a highly monodisperse particle size distribution were produced by a two-step microsuspension method. This process is based on the activation of monosized polymer seed particles by the introduction of a low-molecular-weight material, which leads to a large increase in the monomer swelling capacity of the seed particles. The versatility of the process allows the preparation of polymer monosized compact or macroporous particles of predetermined particle size in the range 1–100 μm and with application of a wide selection of polymeric materials. Underivatized, rigid, porous particles were developed for size-exclusion chromatography in organic solvents. The uniform packing that may be achieved with monosized particles has resulted in chromatographic columns with unusual efficiency and separation capacity. By coating the particle surface with a hydrophilic cross-linked polymer, supports for aqueous phase ion-exchange and size-exclusion chromatography may be produced.

Addition of diazomethane and sulfur ylides to the oxo-group in derivatives of ketoses and aldoses : I. Reactions of 2,3-O-isopropylidene-D-glyceraldehyde

Abstract The reaction between 2,3-O-isopropylidene- D -glyceraldehyde and diazomethane, dimethylsulfonium methylide and dimethyloxosulfonium methylide has been studied. The sulfur ylides yield two epimeric epoxides, 1,2-anhydro-3,4-O-isopropylidene- D -erythritol and 1,2-anhydro-3,4-O-isopropylidene- D -threitol, with a slight preference for the erythro isomer. The reaction with diazomethane yields in addition to the epoxides a methyl ketone, 1-deoxy-3,4-O-isopropylidene- D -glycero-tetrulose. The relative yields of the three products have been discussed on the basis of mechanisms previously proposed for the reactions. The yield of methyl ketone was lowest when the reaction was carried out in pure diethyl ether solution. This solvent also gives the greatest preference for the erythro isomer of the two epoxides. Constitution and stereochemistry for the three products have been shown by synthesis.

Characterization of crosslinked, macroporous, monosized polymer particles

Macroporous, monosized poly(meta-divinylbenzene) and poly(para-divinylbenzene) beads have been prepared by the two-step activated swelling method with toluene or 2-ethylhexanoic acid as pore-forming agents. The type of divinylbenzene isomer as well as the type of porogen has a large effect on both physical and chemical properties of the monodisperse beads. Large pores are obtained with 2-ethylhexanoic acid as porogen while beads prepared in the presence of toluene consist of only small pores and exhibit a shrinking behavior upon drying. The beads have considerable amounts of residual vinyl groups at the end of polymerization, as determined by bromination and Fourier transform IR analysis. The morphology and texture of the particles have been investigated by scanning electron microscopy and atomic force microscopy.

Friedel–crafts reactions of pendant vinyl groups in macroporous monosized poly(meta-divinylbenzene) and poly(para-divinylbenzene) particles

Residual vinyl groups in macroporous monosized polymer particles of poly(meta-DVB) and poly(para-DVB) prepared with toluene and 2-EHA as porogens have been reacted with aluminum chloride as Friedel–Crafts catalyst with and without the presence of lauroyl chloride. In the reaction between aluminum chloride and pendant vinyl groups a post-crosslinking by cationic polymerization takes place. A reaction occurring simultaneously is the addition of HCl to the double bonds. The progress of these reactions was studied by characterization of vinyl group conversion, pore size distribution, specific surface area, morphology, and swelling behavior. In the reaction with aluminum chloride the poly(para-DVB) particles showed a substantially higher conversion of pendant vinyl groups than the particles made of poly(meta-DVB) independent of porogen type. The reaction with aluminum chloride led to a reduced swelling in organic solvents and an increased rigidity of the particles prepared with toluene as porogen. This is confirmed by an increase in the total pore volume in the dry state and a change in the pore size distribution of these particles. Also in the reaction with lauroyl chloride poly(para-DVB) particles have shown a higher conversion of pendant vinyl groups than poly(meta-DVB) particles and the acylation was almost complete at the early stage of the reaction. The swelling in organic solvents is reduced as a result of the incorporation of acyl groups into the particles prepared with toluene as porogen.

Macroporous, monodisperse particles and their application in aqueous size exclusion chromatography of high molecular weight polysaccharides

Abstract Three different types of 15μm macroporous polymer particles (MP) based on poly(styrene- co -divinylbenzene), all with an extreme degree of monodispersity, were prepared by the method of ‘activated swelling’. The type and relative content of low molecular weight compounds used as pore-forming agents (porogens) ensured that the total pore volume was confined to large pores with radii larger than 300 A, and with an increasingly larger fraction of the pore volume shifted towards very large pores (> 2000A). A hydrophilic layer was covalently linked to the particles to eliminate their Hydrophobic character, and they were subsequently tested in aqueous size exclusion chromatography (SEC). Favourable Chromatographic properties generally associated with monosized particles were obtained, and column packing as well as the separations were performed with very low back pressures. The particles were found to be suitable for SEC of a series of high molecular weight polysaccharides, irrespective of their charge (anionic, cationic and neutral). The shift in pore size distribution towards very large pores resulted in a corresponding shift in the range of molecular weights (strictly, hydrodynamic volumes) where separation took place. For particles with 70% of the pore volume confined to pores with radii larger than 2000A, it was estimated that the molecular weight range of polysaccharides of the pullulan type accessible to SEC was extended up to ca. 10 8 . The corresponding value for an extended, rod-like, triple-helical polysaccharide (scleroglucan) was 10 7 .

Formation of the porous structure during the polymerization of meta‐divinylbenzene and para‐divinylbenzene with toluene and 2‐ethylhexanoic acid (2‐EHA) as porogens

Macroporous polymers of pure meta-divinylbenzene (meta-DVB) and pure para-divinylbenzene (para-DVB) have been prepared in the presence of toluene and 2-EHA as pore forming agents. The formation of the pore structure has been studied during the polymerization by pore-size distribution measurements, together with determination of the specific surface area from nitrogen sorption isotherms using the BET treatment. In addition, the morphology and texture have been characterized by SEM during the polymerization process. Large differences in the pore-size distribution among all the polymer samples are found. The polymers prepared in toluene as porogen have a pore-size distribution, which mainly consists of small pores, while large pores appear with 2-EHA as porogen. In the presence of 2-EHA, a major change in the pore-size distribution is also observed when the monomer is shifted from para-DVB to meta-DVB, leading to a bimodal distribution. The texture characterization by SEM shows details and discriminates the samples in consistency with what may be expected from pore-size distribution measurements.

A kinetic study of the polymerization of pure meta-divinylbenzene and pure para-divinylbenzene

The kinetics of the polymerization of pure meta-divinylbenzene (DVB) and pure para-divinylbenzene at 70°C have been studied in the presence of toluene and 2-ethylhexanoic acid. The apparent rate constant ratios (kp/kt)1/2 for these systems have been calculated. meta-Divinylbenzene polymerizes at a higher rate than the para-isomer in both toluene and 2-EHA, and the polymerization rates of meta-DVB and para-DVB before the gel point were both higher in the presence of 2-EHA than in toluene. The monomer conversion at the visual gel point is higher for para-DVB than for meta-DVB. The gel point has also been determined indirectly by size exclusion chromatography, and these results are consistent with the gel times observed visually. The conversion of pendant vinyl groups during the polymerization has been determined by bromination. It is found that the homopolymers of poly(para-DVB) have a substantially higher content of pendant vinyl groups than poly(meta-DVB) both during and at the end of the polymerization. The molecular weight distribution (MWD) prior to gelation has been determined by size exclusion chromatography (SEC). Weight average (Mw); and number average (Mn) molecular weight prior to gelation and of the sol fractions after gelation have also been measured by SEC. There are larger fractions of high molecular weight polymers prior to gelation, when the polymerization was run in the presence of toluene, than in 2-EHA, mainly due to the differences in solvating power of the two diluents.

Addition of diazomethane and sulfur ylides to the carbonyl group in derivatives of ketoses and aldoses-III: Reactions of 1,2-dideoxy-4,5-O-isopropylidene-d-glycero-3-pentulose

Abstract The reactions of diazomethane and dimethyloxo-sulfonium methylide with 1,2-dideoxy-4,5- O -isopropylidene- d - glycero -3-pentulose were studied. The sulfur ylide yielded two epimeric epoxides while diazomethane in addition furnished a homologous ketone. The reaction with diazomethane was carried out with varying concentrations of methanol in the reaction medium, and the relative yields of the three products were determined in each case. The results were explained on the basis of a two-step reaction mechanism proposed earlier. Steric effects and complexation between the positive nitrogen and one of the oxygens were inferred to be important.

Synthetic and spectroscopic studies of 2-C-methyl-erythritol and 2-C-methyl-threito

Abstract The synthesis of 2- C -methyl- d,l -threitol and two isopropylidene derivatives of 2- C -methyl- d -erythritol is described. 1 H and 13 C NMR spectra of these and several related compounds are discussed.

Pre-treatment of diffuse reflectance infrared spectra for quantitative analysis of macro porous polymer particles

Abstract A general pre-treatment procedure for diffuse reflectance infrared spectra is developed for quantitative analysis of macro porous polymer particles. Several different procedures for pre-treatment of diffuse reflectance infrared spectra are compared. Different samples with replicated spectral measurements from manual packing as well as from automatic packing were investigated in order to define the best pre-treatment procedure. Excellent results are obtained by the following four-step procedure: (i) use the packing unit in order to reduce deviations due to surface differences for different packings, (ii) define a zero-absorbance range (100% in reflectance spectrum) or some unchanged peak region to normalise the spectra in order to eliminate deviations between different packings, (iii) correct baseline of the reflectance spectrum peak by peak, and, (iv) finally, transform the baseline-corrected reflectance spectrum into Kubelka–Munk format. The diffuse reflectance spectra so obtained can be then utilised in quantitative analysis, since the relative deviations between the repeatedly measured spectra after this pre-treatment are lower than 5%.