Effect of chemical modifications upon exchange capacity of aminated macroporous styrene-divinyl benzene (PS-DVB) copolymer anion exchange resin

Abstract

The macroporous PS–DVB resin was prepared in the laboratory by suspension polymerization using gelatin as stabilizer and toluene as porogen. This is subsequently nitrated by a mixture of NO and NO2 (called NOx) in a gas phase reaction, and the carbon–nitrogen covalent bonding has been demonstrated by modified Laissagne spot test, FTIR, and ESCA analysis. This has been aminated by reducing the nitrate groups using hydrazine hydrate, and the resultant weak base anion exchange resin was shown to have a one-time exchange property because of its inability to be regenerated by the usual ASTM procedures. The chloroethylated PS–DVB resin is prepared by reacting aminated resin with dichloroethane, and is shown that two molecules of the latter react with every amine group. The regenerable strong-base anion exchange resin is then prepared by quarternizing it with tartiary (trimethyl and triethyl) amines and triphenyl phosphine, and it is shown that these gegen ions have a considerable effect on the exchange ability of the resin. We have found the duration of nitration to be the most important parameter affecting the capacity, and in this work, we report studies for all these gegen ions. It is found that for any gegen ion, the exchange capacity first increases for short times of nitration, reaches a broad maxima of around 5 mEq/g of wet resin with about 69% moisture content (or 15.48 mEq/dry g), and falls slightly for larger times of nitration due to a slight degradation. This is to be compared with commercial chloromethylated resin, which has an exchange capacity of 1.68 mEq/g of wet resin with 43.53% moisture content (or 2.97 mEq/dry g of resin). It is found that the resin with triphenyl phosphine as a gegen ion gives the highest exchange capacity, while the one with trimethyl gives the lowest. To assess the solvation ability of the chloroethylated resin prepared in this work, we evolved three stages of drying consistent with the literature such that in the first stage, unmodified resin loses moisture completely (shell 1 moisture), in the second stage, chloromethylated (commercial anion exchange) resin loses moisture completely (shell 2 moisture), and in the third stage chloroethylated resin loses moisture completely (shell 3 moisture). With the increase in the duration of nitration, the shell 1 and 2 moistures first increase, but after 5 h of nitration they fall to lower asymptotic values for a large duration of nitration. However, shell 3 moisture keeps on increasing and is the highest for triphenyl phosphine gegen ion and the lowest for trimethyl amine. This increased solvation ability of chloroethylated resin is likely to be responsible for higher exchange ability of the resin reported in this work. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1735–1748, 2001