Reactions of Halomethylated Polymers
Many known reactions of the halomethyl groups on polymers are possible. One can, for instance, convert poly (chloromethyl styrene) to poly (hydroxymethyl styrene) [183]. Also, iodomethylated polystyrene can be treated with triethyl phosphite in order to carry out an Arbuzov reaction [192]:
Chloromethylated polystyrene can also be converted to a phosphonium salt for use in the Wittig reaction [193]:
The product of areaction of chloromethylated polystyrene and triphenylphosphine can also convert to nucleophiles [194]. In addition, use of a phase transfer catalyst converts soluble chloromethylated polystyrenes to phosphine oxides. Reactions with dioctyl phosphine can serve as an example [195]. Sometimes phase transfer reactions are easier to carry out than conventional ones. This is the case with a Witting reaction. Both linear and cross-linked chloromethylated polystyrenes react smoothly with triphenylphosphine to give derivatives that react with various aldehydes [196, 197]. Phase transfer catalysts can also be used in carrying out nucleophilic substitutions with the aid of sulfides, like tetrahydrothiophine [198]:
Whenchloromethylated cross-linked polystyrene is reacted with potassium superoxide, the yield depends upon the type of solvent used. In dimethylsulfoxide, in the presence of 18-crown-6 ether, the conversion to hydroxymethyl groups is 45%. In benzene, however, it is only 25%. High conversions are obtained by catalyzing the reaction with tetrabutylammonium iodide in a mixture of solvents. This results in 85% conversions to hydroxymethyl groups, while the rest become iodide groups [199]. Quaternary salts are more effective than crown ethers in reactions with salts of oxygen-anions, such as carboxylate and phenolate [200]. On the other hand, lipophilic crown ethers, like dicyclohexyl-18-crown-6, exhibit higher catalytic activity than the quaternary salts in reactions with salts of the sulfur anions. Also, the catalytic activity of the phase transfer catalysts toward nitrogen anions is intermediate between that toward oxygen and that toward sulfur anions. Solid–liquid two-phase systems generally give higher degrees of conversion than do liquid–liquid systems. When, however, lipophilic phase transfer catalysts are used with lipophilic reagents, high degrees of substitutions are achieved in liquid–liquid two-phase systems [200]. Conversion of chloromethylated styrene to anionic exchange resins is done commercially by amination reactions to form quaternary ammonium groups [201, 202]. This reaction can be illustrated as follows [203]:
The kinetics of amination of chloromethylated polystyrene with monohydroxy dialkyl tertiary amines shows that the reactions proceed in two steps, at two different rates. The rate changes take place at conversions of 45–50% [205]. These rates are favorably influenced by increases in the dielectric constants of the solvents [204]. Two different rate constants also exist in reactions with 3 alkyl aminopropionitrile.
