Charge-Shifting Polycations with Tunable Rates of Hydrolysis: Effect of Backbone Substituents on Poly[2-(dimethylamino)ethyl acrylates]

Abstract

While polycations based on 2-(dimethylamino)ethyl methacrylate and 2-(dimethylamino)ethyl acrylate are used in applications ranging from biomaterials to wastewater treatment, few studies have considered the remarkable differences in the hydrolytic stabilities of the respective ester groups. Here, we describe how the nature of nonmethyl α-substituents affect the rates of ester hydrolysis of such polymers, with an emphasis on the resulting shift of net polymer charge from cationic toward anionic. We introduce 2-(dimethylamino)ethyl 2-hydroxymethyl acrylate (DHMA) as a new, very hydrolytically labile, cationic monomer that can be used to form homopolymers as well as a means to tune copolymer hydrolysis. DHMA synthesis and free radical polymerization are described, including reactivity ratios for hydroxyl-protected derivatives of DHMA and 2-(dimethylamino)ethyl acrylate (DMAEA). Hydrolyses of PDHMA, P[DHMA-co-DMAEA], PDMAEA, and PDMAEMA in pH 5 and 7 buffer are reported. The presence of the hydroxymethyl α-substituent in PDHMA led to rates of hydrolysis 2−3 orders of magnitude faster than the already rapid hydrolysis of PDMAEA. Furthermore, hydrolysis rates of P[DHMA-co-DMAEA] copolymers were shown to increase as the DHMA mole fraction increased. As a result, a new route to adjusting the charge-shifting rates of such polycations in aqueous media is described.

A Mechanistic Study of the Hydrolysis of Poly[N,N-(dimethylamino)ethyl acrylates] as Charge-Shifting Polycations

“…5 In addition, we have observed pH-dependent hydrolysis for some DMAEAcontaining polymers. 6,7 Thus, it seemed worthwhile to examine the hydrolysis of DMAE esters in polymeric systems in greater detail.…”

Facile Synthesis of Tertiary Amine Pendant Polymers by Cu0-Mediated ATRP under Aqueous Conditions

“…al have demonstrated a related phenomenon for monomeric DMAEMA, where the rate of ester hydrolysis shows a plateau near the p K a of 8.4 due to a trade-off between hydroxide concentration and monomer protonation . Studies have also established a significantly decreased hydrolysis for PDMAEMA due to the hydrophobicity of the polymer backbone. , As the hydrophilicity increases with protonation of the pendant amine groups, this shielding effect would be reduced to enable a faster rate of hydrolysis. With PDMAEMA demonstrating a p K a of 7–7.5 dependent on molecular weight, this is likely a driving factor for decreased control of the polymerization near neutral pH.…”

“…This effect may be coupled to the increase in solubility accompanied by protonation of the tertiary amine pendant groups. PDMAEMA has been shown to have a much slower rate of hydrolysis than monomeric DMAEMA, generally attributed to the increased hydrophobicity along the polymer backbone. , At high pH, the high hydrophobicity of the polymer backbone may serve to shield the active end groups from hydrolytic attack. Indeed, van de Wetering et.…”

Preparation of amphiphilic copolymers via base-catalyzed hydrolysis of quaternized poly[2-(dimethylamino)ethyl methacrylate]

“…14–16 Regardless of the application field, the hydrolytic stability of all compounds must be taken into consideration. The degradation of poly[2-(dimethylamino)ethyl acrylate] (PDMAEA) has already been extensively studied, 17–22 indicating that PDMAEA indeed can decompose fairly easily in the aqueous medium. In contrast, researchers revealed that its methacrylic analog, poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), appears to be rather insensitive to hydrolysis.…”

“…In contrast, researchers revealed that its methacrylic analog, poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), appears to be rather insensitive to hydrolysis. 19,21,23 Those studies, however, can be criticized for focusing primarily on hydrolysis at acidic or neutral pH, often omitting base-promoted hydrolysis.…”