Polystyrene resins bead diameter

Typical solid supports used in organic syntheses are resin beads formed from cross-linked polystyrene (PS 40-150 pm diameter), polystyrene-... 

FIGURE 19.3 Schematic of a cation resin bead showing the polystyrene chains with sulfonic groups, the divinylbenzene cross-links, and the active sulfonic groups where the ion exchange occurs. Because the void spaces between the polymer chains and crosslinks contain water, the effective ion-exchange surface area of the bead is not limited to its outside diameter. 

Sevenich and Fritz [9] published a comprehensive study of metal cation selectivity with resins of a more modern type. The studies were made on a column packed with a 12% cross-linked polystyrene-divinylbenzene resin 12-15 mm in diameter and with an exchange capacity of 6.1 pequiv/g. The resins were prepared by rapid sulfonation so that the sulfonic acid groups are concentrated on the outer perimeter of the resin beads [10]. 

The deposition of latex particles on the cationic resin beads is almost certain to occur, but the amount of latex polymer lost in this way is likely to be small. For example, a monolayer of polystyrene particles deposited on the surface of 1 g of 0.5mm-diameter cationic resin beads amounts to 1.3, 0.47, and 0.24 mg for particle sizes of 1760A, 640X, and 330X, respectively. From the proportions of latex and ion-exchange resin used in these experiments, this corresponds at most to about 1% of the latex polymer. Of course, the particles may deposit to form more than one layer, but the number of layers that can be formed by this mechanism is limited moreover, the formation of several such layers would remove only a minor pro-... 

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. 

Macroporous and isoporous polystyrene supports have been used for onium ion catalysts in attempts to overcome intraparticle diffusional limitations on catalyst activity. A macroporous polymer may be defined as one which retains significant porosity in the dry state68-71 . The terms macroporous and macroreticular are synonomous in this review. Macroreticular is the term used by the Rohm and Haas Company to describe macroporous ion exchange resins and adsorbents 108). The terms microporous and gel have been used for cross-linked polymers which have no macropores. Both terms can be confusing. The micropores are the solvent-filled spaces between polymer chains in a swollen network. They have dimensions of one or a few molecular diameters. When swollen by solvent a macroporous polymer has both solvent-filled macropores and micropores created by the solvent within the network. A gel is defined as a solvent-swollen polymer network. It is a macroscopic solid, since it does not flow, and a microscopic liquid, since the solvent molecules and polymer chains are mobile within the network. Thus a solvent-swollen macroporous polymer is also microporous and is a gel. Non-macroporous is a better term for the polymers usually called microporous or gels. A sample of 200/400 mesh spherical non-macroporous polystyrene beads has a surface area of about 0.1 m2/g. Macroporous polystyrenes can have surface areas up to 1000 m2/g. 

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 %, %,... 

Cross-linked polystyrene (PS)-based resins are most commonly used for routine SPPS. Beads of 200 to 400 mesh size distribution (corresponding to a diameter of about 50 pm) and a loading of 0.5 to 0.8 mmol/g present good characteristics for polymer swelling in solvents such as DMF and DCM, diffusion of reactants into the polymer matrix, and accessibility of linker sites buried into the bead. For larger peptides (more than 25 amino acids) or more difficult sequences, a lower loading is required (0.1-0.2 mmol/g). 

Both of the periods of linear temperature rise AT, and AT2 were used to calculate power (see Figure 8). The plots are normalized with respect to the maximum value using both periods and were shown to be very similar. Several different absorbing coatings were used glues (polystyrene cement and UHU), epoxy resins, silicone rubber, polyurethane varnish, and cellulose lacquer. The diameter and length of the beads were varied within the ranges 0.5-0.8 mm and 0.68-1 mm. 

The synthesis of highly substituted pyrrolidines was performed using commercially available monodisperse polystyrene Wang resin from Rapp Polymere (Tubingen, Germany). The diameter of the beads was 160 pm. 

The carrier may consist of styrene copolymer beads with a diameter of 200-600 jum and a bidisperse size distribution, and the toner may consist of modified natural resins or synthetic resins such as polystyrene or phenol-formaldehyde, with a particle diameter of 5-15 jim. 

In the incipience of the methodical development, after some tests with different types of supports, Merrifield had already selected from the gigantic palette of organic and inorganic polymers the commercially available beaded polystyrene (200-400 mesh, 80—20 /i diameter), cross-linked by 2% divinylbenzene as the most suitable up to that time for the purposes of peptide synthesis on solid phase. Today there are series of investigations to find better supports for use in Merrifield s synthesis (for comparison, see the review articles of Merrifield [16, 35] and Meienhofer [33]). But in all cases the improved properties of novel carriers or modified polystyrenes concern only one or two of the above-mentioned necessary parameters — e.g., mechanical stability or strengthened C-terminal bond of an amino acid to the carrier — whereas nearly all the other characteristics for a suitable solid phase turn out to be less favourable, compared to the original Merrifield resin. 

Two polymeric supports have classically been nsed in batchwise SPPS. The first is polystyrene polymer cross-linked with 1% of 1,3-divinyl benzene. A typical dry bead has a diameter of 50 fj,m that swells five- to sixfold in DCM or DMF (144). The second was developed on the basis of the idea that the polymeric backbone should be of similar chemical composition, a polyamide, as the peptide backbone (11). Thns, copol5nnerized dimethylacrylamide, ATjAT -bisacryloylethylenediamine, and acryloylsarcosine methyl ester, or polyamide resin, was developed (146). Polyamide snpports are commercially known as Pepsyn resin. Many other supports have been developed that are compatible with batchwise SPPS and are summarized in the more comprehensive reviews (7,10-20,109). 

Two basic types of packings have been used in LC, pellicular and porous particle. The original pellicular particles were spherical, nonporous. glass or polymer beads with typical diameters of 30 to 40 pm. A thin, porous layer of silica, alumina, a polystyrene-divinyl-benzene synthetic resin, or an ion-exchange resin was deposited on the surface of these beads. Small porous microparticles have completely replaced these large pellicular particles. In recent years, small (- 5 pm) pellicular packings have been reintroduced for separation of proteins and large biomolecules. 

If a polymer product is required in particulate form, then suspension polymerization is especially suitable. The energy required to disperse monomer drops is lower than that required to break up the finished polymer. Also, drop size control before polymerization is easier to achieve than particle size manipulation of granulated polymer. Suspension polymerization provides a good route to functionalized particles such as those used in ion-exchange resins. Expandable polystyrene beads are also made by suspension polymerization. When a product is to be used in bead form , initial drop diameters can be as large as 1-2 mm [1]. 

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