Perfluoroalkyl End-Capped Poly(ethylene oxide). Synthesis, Characterization, and Rheological Behavior in Aqueous Solution

A series of perfluoroalkyl end-capped poly(ethylene oxide) (PEO) of molecular weight M n = 10 000 and 20 000, noted F-HEUR-10K and F-HEUR-20K, with a well-defined structure were synthesized in two reaction steps. The reaction of PEO with a large excess of isophorone diisocyanate (IPDI) leads to an isocyanate-terminated prepolymer which is then reacted with the semifluorinated alcohol [C 8 F 17 (CH 2 ) 11 OH]. Experimental conditions were improved to prevent polycondensation in the first step of the synthesis. The degree of functionalization is controlled by 19 F NMR. The influence of the terminal perfluorinated group on the linear viscoelasticity of aqueous solutions has been investigated as a function of the polymer concentration C pol, PEO chain length, degree of functionalization, surfactant (SDS), and temperature. A steep increase of the static viscosity η 0, attributed to the sol−viscoelastic transition with the formation of a multiconnected network, is observed at C pol ≈ 1 wt %. The stress relaxation function G ( t ) is best fitted by a stretched exponential G ( t ) = G 0 exp[−( t /τ) α ], where G 0 is the elastic plateau modulus. The relaxation time τ and static viscosity η 0 were found to be temperature-dependent according to the Arrhenius law. The hydrophobic character of the end caps reinforced by the perfluorinated segments leads to larger relaxation times (several hundred seconds) and higher activation energies (≈120 kJ mol -1 ) compared to those of hydrocarbon HEUR-type associative polymers.