Abstract: Stable boron resins of high selective absorbent power, their production process, and processes of using said boron resins. The boron resins include a polyacrylic matrix functionalized with quaternary ammonium groups, an epoxy group and phenylboric groups in accordance with general formula (I): ##STR1## in which P, R, R.sub.1, R.sub.2, R.sub.3, Y and X.sup.- are as defined in the text. The resin is prepared by condensing an acrylic resin with an epihalohydrin and then with a halide or hydroxide of an oxiphenyl-aminophenyl- or thiophenyl-boroxin or their alkyl derivatives. Compared with similar currently known resins, the resins of formula (I) have improved selectivity in sugar preparation. They can be used for purifying lactulose.