Divinylbenzene cross-linked polystyrene

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

Chromosorb and Porapak series are divinylbenzene cross-linked polystyrene copolymers. Different members of the series vary in surface area and average pore diameter. Separations range from free fatty acids to free amines. Alcohols from methanol to pentanol can be separated on Porapak Q or Chromosorb 102. The maximum operating temperatiue is about 250°. 

Although l-aIkyl-4-(dialkylamino)pyridinium salts are moderate catalysts for the nucleophilic displacement of chloride, for example, by fluoride ion. their application is limited by their expense. To enable the separation of the catalyst from the product and thus facilitate reuse, immobilized aminopyridinium salts on divinylbenzene cross-linked polystyrene gels of type 3 and 4 are used (see Table 12). The catalytic activities of 3 and 4 were the same after recycling, even after they were reused 8 limes. ... 

Most synthetic methods for the generation of peptide libraries have been derived from various multiple parallel peptide synthesis techniques developed since 1984.bs-i l Consequently, the sohd supports used for hbrary synthesis are essentially the same as those used for multiple peptide synthesis. Standard divinylbenzene cross-linked polystyrene resins are typically used for hbraries that are cleaved from the resin and screened in solution.P Polyoxyethylene-grafted polystyrene resins,f l or acrylamide-polyoxyethylene copolymers, P on the other hand, are the sohd supports of choice for the synthesis of resin-bound peptide hbraries screened in sohd-phase binding assays.P Such resins are compatible with both organic solvents used for peptide synthesis, as well as aqueous buffers used in the bioassays. Various segmental supports previously employed for multiple peptide syntheses have also been utilized for the synthesis of peptide libraries, including polypropylene pins, PI cotton,t cellulose membrane,and glass shdes.P ... 

Columns packed with porous, polymeric particles such as divinylbenzene cross-linked polystyrene, substimted methacrylates, and polyvinyl alcohols can also be used for HPLC method development " as can modified alumina and zirconia stationary phases. ... 

When an electrical potential gradient is imposed on the stack, alternate compartments become enriched and depleted in sodium chloride. A typical module of an electrodialytic salt plant has 1500 pairs of membranes, each with an effective membrane area of 1 m2. The current density is 3.65 A/dm2 at 620 V with a membrane spacing of about 0.75 mm. A brine concentrate containing about 118 g/1 of chloride can be attained. The overall current efficiency is 73% for Na+ and 85% for Cl". Typically, the membranes are divinylbenzene cross-linked polystyrene with sul-phonic acid, or quaternary ammonium exchange groups the exchange capacity is 1.8 to 2.8 meq/g at 25 °C34). 

Mg2" " > Ca2" " > Sr2" " > Ba2" " which is the inverse order of exchange selectivities. The spread in selectivities for the alkaline earth ion series is much smaller compared to that of the alkali metal ions however. The values for the normal form of Nafion in Table II are similar to those of a 4% divinylbenzene cross-linked polystyrene sulfonate resin Mg2" ", 2.23 Ca2" ", 3.14 Sr2" ", 3.56 Ba2" ", 5.66 (12). Resins of 8% and 16% cross-linking have a much larger spread than do these values thus the enhancement in... 

Obviously, the incorporation of an electron-withdrawing substituent in the polymer-supported benzotriazole ring should enhance its reactivity. Thus, the sulfonamide-substituted HOBt resin 34 (Section 7.3) has been obtained by reaction of aminomethylated divinylbenzene cross-linked polystyrene with the sulfonyl chloride 116 to give supported sulfonamide 117, followed by typical hydroxybenzo-triazole formation (Scheme 7.37) [128]. The effect induced by the sulfonamide group was determined by measuring the acidity of non-polymeric analogues, showing a pKa of 3.59 for the sulfonamide-substituted HOBt, and a pKa of 4.64... 

Since the invention of SPPS, divinylbenzene-cross-linked polystyrene has been the predominant solid support used. There have been several alternatives developed along the way, with the most important advancement being the introduction of PEG, including PEG-grafted polystyrene resin [39, 40] and all-PEG-based resin (ChemMatrix) [41, 42]. PEG-based resins can produce crude products with better quality than the polystyrene resins, particularly in the case of difficult sequences [43]. This superiority is explained by the H-bond acceptor function of PEG which interrupts peptide inter-chain H-lxMiding, effectively inhibiting peptide chain aggregation [44],... 

For batchwise synthesis, the base matrix used is almost invariably 1% divinylbenzene cross-linked polystyrene (PS). It is relatively inexpensive to produce, swells in the solvents most commonly used in peptide synthesis, namely DCM, DMF, and NMP, and can be readily functionalized using the Friedel-Crafts reaction with chloromethyl, aminomethyl, and benzhydrylamino groups. 

Later, Kobayashi and coworkers reported on a new type of microencapsulated osmium tetroxide using phenoxyethoxymethyl-polystyrene as support [40]. With this catalyst, asymmetric dihydroxylation of alkenes has been successfully performed using (DHQD)2PHAL as a chiral ligand and K3[Fe(CN)6] as a cooxidant in H20/acetone (Scheme 1.16). This dihydroxylation does not require slow addition of the alkene, and the catalyst can be recovered quantitatively by simple filtration and reused without loss of activity. With a divinylbenzene-cross-linked polystyrene microencapsulated OSO4 and a nonionic phase transfer catalyst (Triton X-405), this system can be run in an aqueous system [41]. 

---