Synthesis of novel polyethyleneimine derivatives by stepwise, reversible blocking of primary and secondary amines

In the design of polyethyleneimine derivatives for use as catalysts and binding media, the placement of reactive and hydrophobic groups previously has been limited by the specificity of the addition reaction. In this paper is described a protocol to limit the sites of addition of nucleophiles and long-chain alkanes to tertiary amines and the less reactive of the secondary amines. Three blocking groups for the primary and secondary amines were tested, but only trifluoroacteylating reagents left the polymer reactive to substitution on the tertiary amines with halogenated alkanes. The secondary amines that resisted trifluoroacetylation were blocked with either tert-butyloxy carbonate or trimethylsilyl carbonate. The tertiary amines were quaternized with iodododecane or dodecyl benzyl chloride. After removal of the trifluoroacetyl groups, the polymer amines were inactivated by methylation, which proceeded to 93% completion. The 7% of the amines that were not quaternized were largely tertiary, since propylene sulfide, which reacts only with secondary and primary amines, was substituted onto the polymer only to the extent of 0.2% total amine, as quantified by the indirect method of P. H. Butterworth, F. Baum, and J. W. Porter (1967, Arch. Biochem. Biophys., 118, 716–723). The sulfhydryl group did not oxidize over at least 14 days. This is the first stable sulfhydryl-containing synthetic polymer that has been reported.