We report on the role of the chemical structure of polyphenol pendant groups in linear antioxidant polymers in their assembly and chain intermixing within layer-by-layer (LbL) films, as well as in the antioxidant performance of interfacial assemblies. When assembled with poly(ethylene oxide) (PEO) within hydrogen-bonded films, the antioxidant polymers-poly(3,4-dihydroxybenzyl methacrylamide) (P2HMA) and poly(3,4,S-trihydroxybenzyl methacrylamide) (P3HMA)-which contain catechol- and gallol-like moieties, respectively, generated films with drastically different structure and functionality. Specifically, while catechol-based P2HMA deposited within LbL films linearly with a low increment of mass increase per step, the growth of P3HMA/PEO films was strongly exponential. Dramatic differences in chain intermixing and layering in these films are revealed by the application of neutron reflectometry using deuterated PEO, dPEO, to create marker layers. Differences in film structure strongly affected film antioxidant performance, as demonstrated by the radical scavenging assay. While assembled P3HMA was fully available for scavenging 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(center dot+)) radical cations, in assembled P2HMA, radical scavenging was restricted to the top similar to 35 nm of the LbL film, highlighting the effect of LbL film structure on antioxidant performance.