The possibility of adjusting the degree of hydrophilic functionalization in polymeric microparticles with a hydrophobic skeleton makes it possible to obtain adsorbents and catalyst microparticles that may show better performance. In this regard, in this study, gel-type poly(styrene-co-divinyl benzene) microparticles were chloromethylated and subsequently aminated, and the quantitative effect of the chloromethylation reaction conditions on the final degree of functionalization achieved were examined. In the chloromethylation route, methylal, thionyl chloride, and a Friedel-Craft catalyst were used. From the experimental results, two models were obtained by multiple linear regression relating the chloromethylation conditions to the anion-exchange capacity (AEC) achieved and to the replaceable chlorine content, according to which the achievement of a high degree of useful functionalization within the microparticles entailed chloromethylation with low methylal/polymer molar ratios and high thionyl chloride/polymer molar ratios, relatively high temperatures, and short reaction times; all of these values were within the ranges used in this study. Additionally, we found that the highest values of AEC could be reached with a methylal/thionyl chloride molar ratio close to unity. The models obtained could be useful for the synthesis of microparticles with required degrees of functionalization, that is, with the chosen hydrophilicity/hydrophobicity ratio. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4054-4065, 2013