Thermo-associating polymers based on cross-linked 2-acrylamido-methylpropane sulfonic acid, part A: Synthesis and solution behavior

Abstract

A novel thermo-thickening hydrophilic copolymer (CGBA) was prepared by free-radical copolymerization of sodium 2-acrylamido-2-methylpropane sulfonic acid (NaAMPS) with a newly-synthesized thermo-sensitive macromonomer (BA) and cross-linking N,N’-methylenebisacrylamide (MBA) in aqueous solution under optimal conditions. Its aqueous solution viscosity behavior with respect to temperature was preliminarily evaluated in comparison with its cross-linked sulfonated copolymer (CPAMPS) counterpart (without BA side-chains). Particular attention is dedicated to the thermo-thickening of the aqueous copolymer solutions as studied by the viscosity measurements. In pure water, and above 0.5 wt.%, CGBA manifested an abrupt macroscopic property above the critical association temperature (Tcass), while CPAMPS exhibited shear-thinning behavior following an Arrhenius law under the same conditions. The composition and length of BA side-chains were identified as the key parameters to envision the self-assembling behavior of CGBA. The results obtained from complementary experiments, performed by proton nuclear magnetic resonance (1H-NMR), Differential scanning calorimetry (DSC), and pyrene fluorescence showed the phase transition of BA side-chains above the Tcass. In addition, well above the Tcass (70 and 80 °C), the oscillatory shear experiments proved that the storage and loss modulus could be fitted with the single relation time Maxwell model at low frequencies. Furthermore, the magnitude of the thickening effect and the Tcass could be modulated using external factors such as shear rates, salinity, and pH. This, in combination with the cost-effectiveness, and the need to further broaden the established theory of thermo-sensitive comonomer, make this copolymer especially interesting for application not only in polymer flooding, but also in drilling fluid.