A series of well-defined poly(styrene-co-maleic anhydride) copolymers (PSMA) allowing controlled grafting density and distribution of long alkyl side chains (C12 and C22) was synthesized and investigated as viscosity modifiers for two mineral base oils (API Group II and III). The PSMA copolymer backbones (multisite, multiblock, diblock, alternating linear, alternating star) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using an industrial chain transfer agent (CTA-Ester) and subsequently esterified using long alkyl alcohols (lauryl and behenyl alcohol). The influence of grafting density and distribution, backbone, and side chain length of the polymers on the pour point (PPT) of blended fluids was investigated. The viscosity index (VI) and thickening efficiency (TE) were also studied. All the polymers showed improvement of base oil properties (PPT, VI, and TE). The alternating PSMA materials (high density of side chains) functionalized with shorter alkyl chains (C12) were found to be more efficient as pour point depressants (PPDs), regardless of the oil type and the molar mass or architecture of the polymer tested (Delta PPT = -36 degrees C and -30 degrees C in oil groups II and III, respectively). A poly(lauryl acrylate) (PLAc) sample was also synthesized and used for comparison, showing the benefit of having styrene in the copolymer additive composition. The VI and TE properties were shown to be dependent on molar mass and architectures used, where the best results were obtained for the high molar mass PSMA star.