Effect of Aromatic Pendant Spacer Length on the Performance of Terpolymer Viscosity Reducers for Heavy Oil

Viscosity reducers are critical for heavy oil exploitation and transportation. In this study, three terpolymers with varied aromatic spatial topologies─poly(stearyl acrylate- co -styrene- co -maleic anhydride) (SSRM), poly(stearyl acrylate- co -allylbenzene- co -maleic anhydride) (SALM), and poly(stearyl acrylate- co -4-phenyl-1-butene- co -maleic anhydride) (SPEM)─were synthesized via radical polymerization and characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ( 1 H NMR), gel permeation chromatography (GPC), and thermogravimetry (TG). Rheological tests evaluated viscosity reduction efficiency, while differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic light scattering (DLS), and scanning electron microscopy (SEM) investigated the induced evolution of asphaltene microstructures. Results indicated that SPEM achieved the highest net viscosity reduction rates of 79.24% (Shengli) and 86.36% (Daqing). Specifically, SPEM reduced asphaltene aggregate diameters from 1068.0 to 326.6 nm and expanded aromatic interlayer spacing from 0.355 to 0.453 nm. This enhanced effect is attributed to SPEM’s flexible ethylene spacer, which facilitates aromatic ring insertion into asphaltene stacks via π–π interactions. These findings demonstrate that the spatial topology of functional groups significantly influences the efficacy of viscosity reducers, providing a valuable reference for the molecular design of viscosity reducers.