Oligo(ethylene oxide) side‐chain steric screening effects on conductimetric properties of grafted poly(4‐vinylpyridinium) salts in aqueous solutions

Abstract

A set of poly[N-oligo(ethylene oxide)yl 4-vinylpyridinium tosylate] (P4VOEOOTs) has been prepared by spontaneous polymerization of 4-vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on every backbone pyridinic moiety. The P4VP15Ts, P4VP164Ts, P4VP350Ts and P4VP750Ts aqueous solution conductivities were determined in the concentration range from 6 × 10 −4 to 10 −2 M at 25 • C. The variation of the conductivity versus concentration of the investigated system exhibits typical polyelectrolyte behaviour. The polyelectrolyte mobility was found to be dependent on the oligo(ethylene oxide) (OEO) side-chain length. Manning's rod-like model fails to describe these results. A simple steric effect is proposed to explain the influence of the OEO length.

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“…This is likely due to an enhanced screening of the charged groups of the polyion by the octyl chain. Similar results have been obtained by Benmansour et al on poly (4‐vinylpyridinium) grafted with oligo(ethylene oxide) of different size 6. This behavior does not follow Manning's counterion condensation theory, which predicts a decrease of Λ when the chain radius increases, as a more bulky hydrophobic substituent reduces the mobility of the polyion, and hence Λ.…”

“…The disagreement between predicted and experimental results can be attributed to various effects, which are not assumed by Manning in his theory, like polyion–polyion interactions, a different (lower) dielectric constant (ε) in the immediate neighborhood of the polyion than that in the bulk, which implies a greater interaction between counterions and polyions, various conformations of the chains, which could lead to a greater charge density parameter (ξ) than that calculated from the chemical structure of the chain assumed to be in a rod‐like conformation, and so forth. Such discrepancy between experimental and predicted Λ values, explained by the authors in a similar way, was also noticed for other polyelectrolytes in aqueous solution 6, 14, 28…”

“…It is well‐known that polyion–counterion interactions, and hence, the properties of ionic polymers in solution depend on various parameters related to the characteristics of the polyelectrolyte chain, the counterion, and the medium properties. The polyelectrolyte characteristics that affect the polyelectrolyte solution properties are the chemical structure of the monomer units, the chain length, the charge density, the type of the ionic groups, polyelectrolyte concentration, and so forth 5–11. The counterions influence the polyelectrolyte solution properties by their size, valency and polarizability, and the water structure around the counterion 12–16.…”

“…Moreover, the electrolytic conductivity measurements are rapid, inexpensive, and sensitive, being able to be carried out with a high level of confidence over a wide range of concentration, far below the overlap concentration ( c *) 4. Conductivity measurements for many synthetic polyelectrolytes have been reported,5, 6, 8, 9, 12–14, 17, 22, 24 but only a few studies on the natural polymers (such as polysaccharides) and their derivatives can be found 26–28. In recent times, a growing interest has been noticed in the study of the behavior of ionic polysaccharides in solution, taking into account their involvement in many processes in molecular biology 29.…”

Transport properties of some cationic amphiphilic polysaccharides: Effects of the side‐chain length and solvent polarity

“…Charged polymers, called amphiphilic polyelectrolytes , exhibit solution properties resulting from the competition between the hydrophobic and electrostatic interactions. Dilute solution properties of amphiphilic polyelectrolytes are influenced by many factors related to the molecular variables that are characteristic of the polymers chains (the chain length, charge density, polyelectrolyte concentration, length and content of hydrophobic groups, and sequence distribution of charged groups and hydrophobic units along the polymer chain), the counterion nature (size and valence), and the medium properties (pH, temperature, and dielectric constant) 12–28. Increasing interest has now been focused on ionic polysaccharides, which present the advantage of being nontoxic and hence involved in many processes in molecular biology 29.…”