Chloromethylated Polystyrene-Divinylbenzene Copolymers

Poly(vinylbenzyl mercaptan) has been described by several authors. The synthesis always follows the same path chloromethylation of polystyrene followed by reaction with thiourea and hydrolysis of the isothiuronium salt 1,53,55,63-65). The redox properties of a polymer obtained from chloromethylated styrene-divinylbenzene copolymers have been evaluated (3). Redox capacities givrai for mercaptyl resins were determined to be 2. W>-5.27 milliequivalents of iodine reduced per gram of (dry) resin in aqueous potassium iodide. The oxidized form of the resin could be easily reduced with 10% aqueous bisulfite fmr a complete redox cycle. Recently polyvinylbenzyl mercaptan resins were prepared directly by treating chloromethylat polystyrene with KSH in dimethyl formamide (66). 

NaHC03 (0.2 g) was added to a suspension of chloromethylated polystyrene-1 % divinylbenzene copolymer (Merrifield resin, 0.5 g, 0.76 mmol/g) in DMSO (3 mL). After stirring for 7 h at 155 °C, the resin was washed successively with H20, MeOH, DMF, CH2C12, and Et20 and then dried under reduced pressure. To confirm the conversion of the chloromethyl resin into the aldehyde resin, two analyses were used FTIR analysis showing the typical carbonyl absorption at 1700.5 cm-1 and microanalysis showing the absence of any chlorine on the resin. The benzaldehyde resin (1.0g, 0.59mmol/g) was suspended in... 

Polymeric supports can also be used with advantage to form monofunctional moieties from difunctional (Hies. Leznoff has used this principal in the synthesis of sex attractants on polymer supports (67). Starting from a sheap symmetrical diol he blocked one hydroxyl group by the polymer. Functionalization of cross-linked polymers is mostly performed by chloromethylation (65). A very promising method to introduce functional groups into crosslinked styrene-divinylbenzene copolymers is the direct lithiation with butyllithium in presence of N,N,N, N -tetramethyl-ethylenediamine (TMEDA) (69, 70). Metalation of linear polystyrene with butyl-lithium/TMEDA showed no exchange of benzylic hydrogen and a ratio of attack at m/p-position of 2 1 (71). In the model reaction of cumene with amylsodium, a kinetic control of the reaction path is established. After 3h of treatment with amyl-sodiuni, cumene is metalated 42% in a-, 39% m-, and 19% p-position. After 20h the mixture equilibrates to affort 100% of the thermodynamically more stable a-prod-uct (72). 

Subsequently D Alello developed the polystyrene-hased resin in 1944 (4). Two years later, polystyrene anion-exchange resins made hy chloromethylation and amination of the matrix were produced. Four principal classes of ion-exchange resins were commercially availahle by the 1950s. These are the strong-acid, strong-hase, and weak-hase resins derived from styrene-divinylbenzene copolymers, and the weak-acid resins derived from cross-linked acrylics. To this day, the most widely used ion exchangers are synthetic organic polymer resins based on styrene- or acrylic-acid-type monomers as described by D Alelio in U.S. Patent 2,3666,007. 

These polymers constitute the largest group to be discussed in this report and this is mainly because polystyrene and poly(chloromethylstyrene), often crosslinked with divinylbenzene, continue to be widely used in the preparation of functional polymers and resin-supported reagents. In fact most of the examples given here refer to the preparation of functional polymers rather than to new materials. This is a rapidly growing area of polymer chemistry and it is not possible to refer, in a compressed review of this nature, to all reports of functionalized styrene-based resins that have appeared in the past two years. This section falls naturally into three parts the first deals with styrene polymers and copolymers, the second with reactions on chloromethylated polystyrenes, and the third deals with styrene-related polymers. 

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