Polystyrene aromatic substitution

The selective electrophilic aromatic substitution carried out by displacement of a metallic substituent (Hg, Sn) ( F-fluorodemetallation) using [ F]p2 or [ F]AcOF remains a method of choice to introduce a fluorine atom on a specific position. In the early preparations of [6- F]fluoro-L-DOPA, the reaction of a 6-substituted mercuric derivative with [ F]acetyl hypofluorite yielded the expected compound in 11 % yield [73,74]. Reaction of a mercuric precursor, free or on a modified polystyrene support P-CH2-COOHg(DOPA precursor) allows the preparation of [ F]fluoro-L-DOPA in an overall yield up to 23 %. The polymer supports are easily prepared, require no special treatment for storage and are convenient to use in automated production [75]. 

When naphthalene is substituted by a polyvinyl aromatic chain polystyrene PS, poly(p-tert-butylstyrene) PTBS or poly(ot-methylstyrene) PMS the course of the metalation is deeply modified (21, 22, 25.). 

It was known that polystyrene and poly- >-methoxystyrene initiated by tin tetrachloride have a branched structure, due to aromatic substitution in the course of the polymerization (186). Haas, Kamath and Schuler (93, 124) studied the ionic chain transfer reaction between a polystyrene carbonium chain and poly-/>-methoxystyrene. They were able to separate the homopolymers from the graft copolymers by extraction with methylcyclohexane. 

Sulfonation of polystyrene occurs by an electrophilic aromatic substitution... 

Step 1 Polystyrene and the phthalimide combine in an electrophilic aromatic substitution reaction... 

The nonpolar polymer that has received the most attention is polystyrene. A few studies have included alkyl-substituted polystyrenes, and the majority support the assumption that polystyrene is representative of nonpolar aromatic polymers in general [60b,d, 68dj. There are, in addition, a few data on not-very-polar polymers with quite different chemical structures where, at least, the mobilities at room temperature are similar to those in polystyrene [55k]. 

The widespread applications of polystyrene derived resins is due to the fact that styrene consists of a chemically inert aUcyl backbone carrying chemically reactive aryl side chains that can be easily modified. As discussed earlier, a wide range of different types of polystyrene resins exhibiting various different physical properties can be easily generated by modification of the crosslinking degree. In addition, many styrene derived monomers are commercially available and fairly cheap. Polystyrene is chemically stable to many reaction conditions while the benzene moiety, however, can be funtionalised in many ways by electrophilic aromatic substitutions or lithiations. As shown in Scheme 1.5.4.1 there are principally two different ways to obtain functionalised polystyrene/DVB-copolymers. 

As shown so far many functionalised resins were obtained by electrophilic aromatic substitution reactions. A very valuable route to other functionalised resins constitute lithiation reactions on polystyrenes as shown by Frechet and FarralF and depicted in Scheme 1.54.9. 

PET reactions of benzylic silanes with polycyano-aromatic compounds have been applied to photoresist and electron-beam resist technologies. "" The photoreaction of poly(4-trimethylsilyl-methylstyrene) in benzene-acetonitrile with DCB affords insoluble polymer via photo-cross-linking, which contains 4-cyanophenyl-methyl groups. In the case of 1,2,4,5-tetracyanobenzene, soluble 2,4,5-tricyanophenylmethyl-substituted polystyrene is produced. But,... 

There are some interesting reports in the literature on reactions carried out on the backbones of polystyrenes. There are also many reports in the literature on aromatic substitution reactions of polystyrene. Only a few, however, are in industrial practice. 

Aromatic isocyanates are used to acylate aromatic substratesand polystyrene . Reaction of trialkylstannyl substituted arenes 214 with phenyl isocyanate at 20 °C in the presence of aluminum chloride affords A-substituted amides 215. ... 

After termination, this gives the block copolymer S-iB-S. Polyisobutylene is the only elastomeric midsegment that can be produced by carbocationic polymerization. There are many aromatic polymers (mostly substituted polystyrenes) that can form the end segments [8]. 

The study of polymer-supported reactions in organic chemistry (Ref 1-6) is a field which has enjoyed rapid growth in the past two decades and has required the preparation of a large number of specialty polymers carrying various functionalities much of this preparative work has been carried out through the modification of a few reactive polymers derived from polystyrene (Ref 7) The chemical modification route is particularly attractive in this instance as polystyrene resins contain aromatic rings which can be modified readily, often by electrophilic aromatic substitutions, while the rest of the molecule (polymer backbone) is relatively... 

The dielectric losses at high frequencies are found to increase in intensity with increasing polarity of librating atomic groups in substituted polystyrenes (Fig. 18). In Ref. [78], the observations have been made on PPFS in which the aromatic nucleus contains the five fluorine atoms. As expected for heavier groups, the frequency of maximum loss drops to 3 cm"10 Hz) and the maximum loss amplitude rises compared to PS. 

Polystyrene is a polymer (Section 12-15) whose subunits are derived from ethenylbenzene (styrene). Although beads of polystyrene are insoluble and rigid when dry, they swell considerably in certain organic solvents, such as dichloromethane. The swollen material allows reagents to move in and out of the polymer matrix easily. Thus, its phenyl groups may be functionalized by electrophihc aromatic substitution. For peptide synthesis, a form of Friedel-Crafts alkylation is used to chloromethylate a few percent of the phenyl rings in the polymer. 

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