| Abstract
| - In this paper, we investigated the interactions between poly(ethylenimine) [BPEI] and the proton by using (H+-glass electrode) potentiometry and titration calorimetry. The measurements were carried out in NaCl aqueoussolutions, at T = 298 K in a wide range of ionic strength (up to I ≈ 5.0 mol·L-1). The protonation constants werecalculated by following different approaches: (a) first, all the protonation constants were considered as true constants(considering BPEI as a simple low molecular weight tetramine); (b) second, the log KH3 was considered as alinear function of p̄ (p̄ = protonation degree); and (c) the log KH3 was considered as a nonlinear function of p̄.The difference in the standard deviation on the fit between (a) and (b) calculations is quite significant, while nofurther improvement is observed by using the (c) model. The protonation enthalpies were calculated from thecalorimetric titrations. In these calculations, all the protonation steps of BPEI were considered as independent ofp̄. The dependence of protonation constants and enthalpies on ionic strength was modeled using the Specific ionInteraction Theory (SIT).
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