Highlight on the Mechanism of Linear Polyamidoamine Degradation in Water

Abstract

This paper aims at elucidating the degradation mechanism of linear polyamidoamines (PAAs) in water. PAAs are synthesized by the aza-Michael polyaddition of prim-monoamines or bis-sec-amines with bisacrylamides. Many PAAs are water-soluble and have potential for biotechnological applications and as flame-retardants. PAAs have long been known to degrade in water at pH ≥ 7, but their degradation mechanism has never been explored in detail. Filling this gap was necessary to assess the suitability of PAAs for the above applications. To this aim, a small library of nine PAAs was expressly synthesized and their degradation mechanism in aqueous solution studied by 1H-NMR in different conditions of pH and temperature. The main degradation mechanism was in all cases the retro-aza-Michael reaction triggered by dilution but, in some cases, hints were detected of concurrent hydrolytic degradation. Most PAAs were stable at pH 4.0; all degraded at pH 7.0 and 9.0. Initially, the degradation rate was faster at pH 9.0 than at pH 7.0, but the percent degradation after 97 days was mostly lower. In most cases, at pH 7.0 the degradation followed first order kinetics. The degradation rates mainly depended on the basicity of the amine monomers. More basic amines acted as better leaving groups.

Reactive degradable linear poly(aminoamide)s: synthesis, post-polymerization modifications and layer-by-layer coating

“…However, the rate of degradation largely depends upon the pH and temperature of the aqueous medium. Since poly(aminoamide)s favor degradation under alkaline conditions (rate of degradation is higher at higher pH), 12 we studied the degradation of indolized-PAA and its crosslinked derivative (PAA-60% M) in two different basic solutions −0.01 M (pH 12) and 0.1 M NaOH (pH 13) solution at 40 °C. As both linear and crosslinked poly(aminoamide)s are insoluble in water, gravimetric method is extremely reliable method of choice to monitor the degradation.…”

“…[9][10][11] Such polymers are biodegradable due to the combination of retro aza-Michael and hydrolysis reactions. 12,13 Due to its biodegradability and biocompatibility, functional poly(aminoamide)s are well known in various biomedical applications such as gene delivery, drug delivery, bioimaging, biosensing, etc. [14][15][16][17][18][19][20][21][22][23][24][25] Beside these conventional applications, very recently poly(aminoamide)s are well explored for environmental remediations and as dynamic materials.…”

Bactericidal Biodegradable Linear Polyamidoamines Obtained with the Use of Endogenous Polyamines

“…Significantly less toxic linear polyamidoamines (PAAs) are the aza-Michael polyaddition products of primary monoamines or bis-sec-amines with bisacrylamides [ 12 , 13 ]. These polymers are particularly useful as anti-metastatic drugs [ 14 ] and as intercellular nonviral carriers of DNA [ 15 ].…”

“…Due to the limited possibility of selecting monomers, their chains are always built of repeating units containing bis-amide derivatives and tertiary amines. Due to such a structure, these polymers are most often difficult to degrade in the conditions of the human body, and some of the degradation products are not biocompatible [ 12 ]. For this reason, various attempts have been made to overcome this problem.…”

Semi-Crystalline Hydrophobic Polyamidoamines: A New Family of Technological Materials?

“…Consequently, PAAs are a polymer class with high structural versatility. In particular, they can be designed to be biocompatible and degradable [ 4 , 5 , 6 ]. All PAAs described so far are highly hydrophilic and in most cases water soluble.…”