Chemical degradation of poly(2-aminoethyl methacrylate)

Poly(2-aminoethyl methacrylate) (PAMA) has a pK_a of approximately 7.6 and is chemically stable in acidic or neutral aqueous solution in its protonated form. However, chemical degradation of PAMA is known to occur in alkaline media as its primary amine groups become deprotonated (He L et al. Macromolecules 2007; 40: 4429-38). In the present work, the effect of temperature, pH and polymer concentration on the rate of PAMA degradation in dilute aqueous solution has been examined. ¹H NMR spectroscopy indicates that both elimination of 2-aminoethanol and formation of 2-hydroxyethyl methacrylamide repeat units occur above pH 9; elimination is observed first and occurs to a greater extent. FT-IR studies of aqueous PAMA solutions aged at pH 12 and 50 °C confirm the presence of anionic carboxylate groups, which suggests that such elimination is simply due to ester hydrolysis. A control experiment suggests that methacrylamide formation occurs via internal rearrangement, rather than by amidation of the remaining ester groups by the eliminated 2-aminoethanol.