Conformational Characteristics of Modified Ethylene-Vinyl Acetate Copolymer (EVA) Facilitate the Pour-Point Depression of Waxy Oils

Molecular architecture of polymers largely determines the efficiency of pour-point depressants (PPDs). Here, alcoholyzed ethylene-vinyl acetate copolymer (EVA) was modified using alkyl acyl chlorides (C n H 2n+1 –C═O–Cl, n = 6, 12, 24, 36) to elucidate how side-chain length governs the rheological behavior of waxy oils. Macroscopic tests, combined with molecular dynamics simulations, show that pour-point depression and viscosity reduction generally improve with increasing side-chain carbon number; however, the incremental gain becomes less pronounced for the longest substituent. The polymer radius of gyration ( R g ) exhibits a piecewise dependence on side-chain length, whereas the backbone R g remains essentially unchanged (1.02–1.03 nm). Junction-region bond angles vary only slightly, indicating negligible local geometric distortion; instead, the dominant response is the redistribution of key dihedral angles, which shifts preferred side-chain orientation and thereby modulates chain extension and flexibility. In the cocrystalline environment with wax molecules, EVA maintains a local wax-rich region that becomes denser as the side chain lengthens, consistent with strengthened van der Waals interactions of wax–EVA and more compact local packing. Moreover, EVA disrupts wax packing and orientational order, constrains wax mobility, and reduces the wax-phase packing order by 18.7%, rationalizing the observed improvements in bulk rheology.