Branched polyacrylamides: Synthesis and effect of molecular architecture on solution rheology

Linear, star and comb-like polyacrylamides (PAM) have been prepared by atomic transfer radical polymerization (ATRP) in aqueous media at room temperature. The influence of the molecular architecture of PAM on the rheological properties in aqueous solution has been investigated. The well-known theory of increased entanglement density by branching for polymers in the melt can also be applied to polymers in the semi-dilute water solutions. We have demonstrated this by investigating the rheological properties of PAM of similar molecular weights with different molecular architectures. Interestingly, the solution viscosity of a comb PAM is higher compared to its linear and star analogues (both at equal span molecular weight, Mn,SPAN, and total molecular weight, Mn,tot). In addition to the pure viscosity, we also demonstrate that the visco-elastic properties of the polymeric solutions depend significantly on the molecular architecture of the employed PAM. The elastic response of water solutions containing comb PAM is more pronounced than for solutions containing either linear or star PAM at similar Mn,SPAN and Mn,tot. The obtained results pave the way for application of these polymeric materials in Enhanced Oil Recovery (EOR).