Crosslinking of poly(allylamine) with esters of diimidic acids in aqueous media

Abstract

Recently, in our laboratory we started work on intra-and intermolecular crosslinked mircrogels of different molecular weights which contain free. amino groups and are soluble in water. The amino groups of the microgels react at anhydrous conditions with aldonolactones (mono-, di-or oligo-saccharides with a lactone group). The resulting sugar-surrounded microgels may be used as models of a living cell and should be suitable to investigate interactions among polysaccharides.Poly(al1ylamine) (PAlA) was found to be a suitable polymer for this purpose. It is soluble only in water and ethylene glycol. For this reason a crosslinking agent was required which reacts selectively with amino groups in aqueous solutions under mild conditions and which does not change the net charge of the polymer when crosslinking is performed.A wide variety of reagents has been studied to crosslink proteins intra-and intermolecularly in aqueous Each crosslinking agent has its own set of advantages and disadvantages in terms of specificity, reactivity, solubility and stability. Hunter and Ludwig4) showed that water-soluble imidic esters react specifically under mild conditions with amino groups of proteins. By the appropriate choice of the pH even the ratio of the reaction rates of aand &-amino groups can be varied5). The resulting amidines can be cleaved again by treatment with ammonium hydroxide to yield the original amino groups4). Since the pKa of amidines is higher than that of amino groups, an amidinated molecule has the same net charge in the acid or neutral pH range as does the unmodified amino group; thus the solubility of the crosslinked protein or polymer should not be affected by this reaction.The synthesis of a number of diimidic ester dihydrochlorides 2 (Eq. (1)) has been described6).OR' I C=N C=NH. HCI