Synthesis, characterization, rheological properties and hydrophobic nano-association of acrylamide/styrene and acrylamide/sodium styrene sulfonate/styrene co- and terpolymers

Abstract

Hydrophobically modified polyacrylamides (HMPAMs) are used as rheological modifier and thickening agent, for example, in enhanced oil recovery, drilling fluids and dying technology. In this work, acrylamide/ styrene (AM/St) copolymers and AM/St/ sodium styrene sulfonate (AM/St/SSS) terpolymer were synthesized by heterogeneous and micellar radical copolymerization methods. Final copolymer composition was determined using 1H-NMR spectroscopy. In comparison to initial mole fraction of St (0.0137), mole fraction of St incorporated into the copolymer chains for heterogeneous sample decreased to 0.0093 while that for micellar sample increased to 0.01386. Microstructures of the synthesized samples were investigated by calculating sequence length of the hydrophobic (St) and hydrophilic monomers. Depending on the polymerization conditions, viscosity- average molecular weight of the synthesized samples varied in the range of 4 × 105 g.mol−1 and 1 × 106 g.mol−1. In the heterogeneous copolymerization method, St was incorporated randomly into the copolymer chains while in micellar copolymerization method, a multi-block distribution of St in the copolymer chain was observed. Strong thickening behavior was observed by increasing copolymer concentration and NaCl concentration. Among other co- and terpolymers, AM/St/SSS revealed the best rheological and thermal properties. Shear thinning behavior was observed for all co- and terpolymers. It was found that rheological properties of the synthesized HMPAMs can be affected significantly by the microstructural parameters and hydrophobic interchain nano-association.