Polystyrene cross-linking

Whereas polymers of sufficiently high molecular weight may be soluble in the common solvents with some difficulty, network polymers do not dissolve, even at elevated temperature. They usually swell depending on the nature and cross-link density. Marcus [10] described the swelling of polystyrene cross-linked by divinylbenzene. 

Figure 8. 31P-CP/MAS solid-state spectrum of polymer-bound (polystyrene cross-linked with 2% divinylbenzene) triphenylphosphine (a), 31P-CP/MAS solid-state spectrum of cis-[PtCl2(PPht-C6H -CH—CH2)2] (referenced to external 85% Hs POJ (b), 31P-CP/MAS solid-state spectrum of a copolymer of 65% styrene, 31% divinylbenzene and 4% cis-/PtCl2(PPh2-C6H -CH CH2)z] after soxhlet extraction (c) and 31P-CP/MAS solid-state spectrum of c s-[PtCl(PPhs)2, (N P )] ClOf after soxhlet extraction (d). All spectra referenced to external 85% HsPOk. (Reproduced from Ref. 21. Copyright by American Chemical Society.)...

Immobilized cryptates. Like the crowns, cryptates have been immobilized on polymeric backbones. A typical system is given by (221) (Cinquini, Colonna, Molinari, Montanari Tundo, 1976). In this case, the polymeric matrix is polystyrene cross-linked with p-divinyl benzene and the cage is connected to this matrix via a long-chain aliphatic spacer group. This reagent is quite effective as a (triphase) transfer catalyst. 

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

Figure 5.16 2,6-Diaminopyridine side chain functionalized polystyrene cross-linked via bis-thymine cross-linking agents.

Figure 1.8 shows an electron micrograph of latex particles made from polystyrene cross-linked with divinylbenzene. Note that these latex particles are not the same as simple polystyrene molecules in a true solution. The particles shown in the figure display a remarkable degree of homogeneity with respect to particle size. Such a sample is said to be monodisperse (in size), in contrast to polydisperse systems, which contain a variety of particle sizes. We have a good... 

Table 2.3. Gel points in polystyrene cross-linked by gamma radiation...

Polystyrene cross-linked with 1-2% DVB is sufficiently flexible to allow intermediates attached to it to react with each other. Terminal alkenes linked to this support can therefore undergo self-metathesis to yield symmetrical, internal alkenes when treated with a suitable catalyst [133,134]. Self-metathesis of support-bound /V-alke-noylated peptides has been used by Conde-Frieboes et al. [133] for the preparation of symmetrical peptidomimetics (Figure 5.17). Various peptides were prepared on cross-... 

PEG-grafted polystyrene is also well suited for reactions with highly reactive orga-nometallic reagents, provided that the support has been dried. PEG-containing polymers are generally more difficult to dry than pure polystyrene. Cross-linked PEG is stable towards Lewis acids, and can be used for SnCl4-mediated allylations of aldehydes with allyl silanes [21],... 

Polystyrenes cross-linked with divinylbenzene commercial resins, such as Lewatit VP-OC 1163 (Bayer AG, Leverkusen, Germany), Amberlite XAD-4 (Rohm Haas, Frankfurt, Germany), and Serdolite PAD I, PAD II, and PAD III (Serva AG, Heidelberg, Germany), have been applied in the adsorption of phenol, chlorophenols, and dihydroxybenzenes from water solutions [90]. Besides, commercial polymethacrylate/divinylbenzene resins, for example, Supelcogel TPR-100... 

Porous polystyrene cross-linked with l,l -(methylene-4,4 -phenylene)bismaleimide (72) shows good recoveries for aniline (la), 1,2- (lj) and 1,3-phenylenediamine (lk) in water solution, probably due to adsorption on the imide moieties. Other cross-linked porous aromatic polymers show poor results with these PAA analytes even if they adsorb efficiently similarly substituted nitroaromatic analytes. Recovery of the analytes from the SPE cartridges can be done with MeOH end analysis was by HPLC-DA-UVD132. 

Fig. 4 Two parallel routes for synthesis of imino-diacetate resins from polystyrene (cross-linking not shown).

Haraguchi et al. recently supported 26 on three different types of cross linked polystyrenes standard cross linked polystyrene, cross linked polystyrene with... 

Merrifield pioneered the solid-phase method for the preparation of polypeptides.146 The typical support used is a chloromethylated polystyrene cross-linked with 1% di-vinylbenzene. A generalized scheme is shown (5.35). 

While Merrifield experimented with the polystyrene cross-linked with 2% and later 1% DVB [55], Letsinger adopted the popcorn polystyrene [54] which relies on less cross-linking agent (0.05-0.2%) to achieve complete insolubility in common organic solvents. Ah of his early ohgodeoxyribonucleohde syntheses by the phos-photriester method were performed on this type of support [53, 58, 59], Other researchers have used popcorn PS as well in the syntheses by the phosphodiester method [144] and, later, more advanced phosphotriester method [145], However, with the widespread use of low cross-linked PS and the advent of polyacrylamide and especially silica gel supports (Section 19.2.3), use of popcorn polystyrene in oligonucleotide synthesis has practically ceased. 

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