A Discussion of the pH-Dependent Protonation Behaviors of Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and Poly(ethylenimine-ran-2-ethyl-2-oxazoline) (P(EI-r-EOz))

Abstract

In this article, we present results of our experimental and atomistic simulation studies of the pH-dependent protonation behaviors of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(ethylenimine) (PEI). The potentiometric titration profiles of the PDMAEMA polymer and its unpolymerized monomer (i.e., DMAEMA) were measured under identical conditions in order to study the influence of the covalent linkage of the amine groups on their protonation behavior. The titration curves of poly(ethylenimine-ran-2-ethyl-2-oxazoline) (P(EI-r-EOz)) random copolymers with varying monomer composition were measured in order to study the effect of the spacing between the EI monomers on the protonation behavior of the P(EI-r-EOz) copolymer. The results of these two sets of measurements demonstrate that the connectivity and tight spacing between amine groups in a polyamine chain causes the retardation of the protonation of the amine groups relative to the same compounds in their isolated state. The same titration measurements were also performed with added NaCl. The results of these measurements demonstrate that added NaCl weakens the electrostatic repulsion between charged amine groups in a polyamine chain and thus enhances the protonation of the chain, and this effect is quite significant at a physiological NaCl concentration of 150 mM. However, on the quantitative level, the effect of added NaCl was found to be very different between the PDMAEMA and P(EI-r-EOz) cases. In PDMAEMA, since the amine groups are located at the termini of the side chains, the interaction between adjacent charged monomers occurs through the aqueous medium, and therefore at a sufficiently high concentration of added NaCl, the amine groups on the chain behave almost identically to their unpolymerized equivalents. In contrast, the electrostatic interaction between two closely spaced charged EI monomers in a P(EI-r-EOz) chain is significantly less influenced by a change of the ionic strength of the medium, because it is dominated by the local dielectric property of the polymer segment located between the charged monomers. This interpretation is further supported by ab initio electron density functional theory (DFT) calculations on model oligomeric compounds whose structures imitate the repeat unit structures of the polymers. Lastly, in connection with potential applications of the PEI and PDMAEMA polymers in gene delivery technologies, it was also examined how complexation with negatively charged polymers at the physiological NaCl concentration (150 mM) impacts the protonation behaviors of the polyamines. We found that the oppositely charged polyanion greatly stabilizes the protonated form of the amine groups on the polyamine chain. However, the proton buffering capacity of the polyamine in the complexed form under the influence of added 150 mM NaCl for the intracellularly relevant pH change was found to be significantly lower than that of the pure polyamine in the uncomplexed state with no added salt.

Charged hydrophilic polymer brushes and their relevance for understanding marine biofouling

“…The wettability data presented in Table 1 shows that PDMAEMA is more hydrophobic than the other polymers, but the difference does not suggest that the materials is uncharged, in which case the hydrophobic nature of the hydrocarbons would be more pronounced. A more thorough investigation of the pHdependence shows that at high pH, of PDMAEMA is uncharged, and collapsed, but both our own unpublished investigations (Yandi et al In preparation) and published data (Lee et al 2011) demonstrate that this is not the case at the pH of ASW, but that PDMAEMA have approximately 10% of the amino residues protonated at a pH of 8.2. Hence, we here refer to PDMAEMA as 'cationic', although the polymer itself is nominally neutral.…”

Universal Conditions for the Controlled Polymerization of Acrylates, Methacrylates, and Styrene via Cu(0)-RDRP

“…Increasing the temperature to 40 °C gave no improvement over the conversion or the control over the MWD (Đ ≥ 1.76), which demonstrates that this combination of initiator, solvent, ligand cannot facilitate the con trolled polymerization of MMA (Table 1, Entry 2 and Figure S2). MBPA, a much less explored initiator, [42][43][44] exhibits high activity and should thus be suitable for methacrylates given they are considered active monomers. 9 Significantly, switching the initiator from EBiB to MBPA gave rise to low dispersities (Ð~1.15) although the conversion did not exceed 79% (overnight) even when the temperature was increased to 40 °C (Table 1, Entries 3-4 and Figure S3-S4).…”

Well-Defined PDMAEA Stars via Cu(0)-Mediated Reversible Deactivation Radical Polymerization

“…[1][2][3] These properties render polyamines a good candidate for a wide range of applications such as gene delivery 4 , waste water treatment 5 , paper making 6 and cosmetics 7 . In comparison to the analogous methacrylate, poly(dimethylaminoethyl methacrylate) (PDMAEMA), poly(dimethylaminoethyl acrylate) (PDMAEA) has attracted further interest due to its ability to provide a timed release mechanism facilitated by its selfcatalysed hydrolysis in water to polyacrylic acid and N,N'-dimethylaminoethanol.…”