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Poly(styrene-co-maleic anhydride)s (SMAs) with different compositions and molecular weight were synthesized through the reversible addition–fragmentation chain transfer polymerization technique. SMAs were converted to poly(styrene-co-octadecyl maleimide)s (SNODMIs) by amidation with octadecyl amine and subsequent imidization. SNODMIs with octadecyl branches were evaluated as flow improvers in the model crude oil with a high content of asphaltenes. The effects of molecular structures, including molecular weight, branch content, and imidization degree, on the effectiveness of SNODMI in reducing the viscosity and yield stress and improving the morphologies of asphaltene particles were thoroughly investigated using a rotational rheometer with parallel plate geometry and a polarizing microscope with a hot stage, respectively. It has been found that efficacy of SNODMI in reducing the viscosity and yield stress of the model crude oil increases with an increasing branch content of SNODMI. (alt)SNODMI with the highest branch content, approximately 45 mol %, achieved the best performance. Too high or too low molecular weight is not beneficial for SNODMI to improve the flow ability of the model crude oil. The appropriate molecular weight (Mₙ = 3500 Da) is required to achieve the optimal effectiveness. The optimal imidization degree of SNODMI is 100% and is independent of the branch content. The addition of SNODMI in a real crude oil has reduced the viscosity and yield stress by more than 90%.

A series of poly(styrene-co-octadecyl maleimide) (SNODMI) with various molecular structures were prepared through RAFT polymerization and subsequent modification with amine. The obtained SNODMIs we...