Polyelectrolytes of high charge density in organic solvents. Synthesis and viscosimetric behavior
Résumé
An easy anion exchange between electrolyte monomers of the quaternary ammonium halide type such as [(2-methacryloyloxy)ethyl]trimethylammonium chloride or 1-vinyl-3-methylimidazolium iodide and various cyanocarbon salts such as 1,2,2-tricyanoethenolate, 1,1,2,3,3-pentacyanopropenide, α,α-dicyano-p-toluoylcyanide, or p-(tricyanovinyl)phenyldicyanomethide readily leads to a series of new hydrophobic electrolyte monomers with yields generally over 70%. [(2-Methacryloyloxy)ethyl]trimethy-lammonium 1,1,2,3,3-pentacyanopropenide is a most representative example. Its free radical polymerization in homogeneous solution (DMF, 60 °C) currently yields atactic chains (Bernoulli stereopropagation process, probability of meso placement Pm = 0.31) of fairly high degree of polymerization (DPw ∼ 1600) which show an unique spectrum of solubility in dipolar organic solvents (dipole moment μ > 2.6 D) covering a very broad range of dielectric constants (∈ ∼ 10-180). Viscosity measurements performed in 13 solvents allow us to analyze the polymer solution properties in three different situations: (a) For good, but weakly dissociating solvent (triethyl phosphate, ∈ ∼ 10), there were no polyelectrolyte effects, (b) For good and fairly to highly dissociating solvents (cyclopentanone...2-cyanopyridine, ∈ ∼ 13-90), as a general trend, polyelectrolyte effects increase with the dielectric constant, but the usual excluded volume effects remain a factor of the number of effective charges per chain, as estimated from the ratio A/B of the parameters of the Fuoss equation in its simplified form (ηred = A/1 + BC0.5). (c) For very poor but very strongly dissociating solvents (formamide, N-methylformamide, ∈ > 100), there were no polyelectrolyte effects at 25 °C and transition to a fairly good solvent at about 50 °C with simultaneous emergence of weak polyelectrolyte effects. These new hydrophobic polyelectrolytes appear as optimized and versatile models for the quantitative analysis of the influence of the usual excluded volume effects and of the specific electrostatic interactions on the static and dynamic solution properties of polyelectrolytes in all possible solvation and dissociation situations.