*1.4. Natural Antioxidant Macromolecules*

Antioxidant polymers are a broad class of polymers, including polylactones [25], polymer nanoparticles integrated with living polymerization techniques [26], poly(b-malic acid) derivatives [27], lignin graft polymers, and polyphenols, which offer unparalleled capabilities in tumor-targeted drug delivery, food fortification [28], biodegradation of polymers, and antimicrobial treatment [29]. Emerging research evidence indicates that hydrophobic antioxidant polymers are effective corrosion inhibitors in steel structures.

The development of green, biocompatible, and biodegradable antioxidants is critical in polymer processing industries, packaging, health, cosmetics, textiles, and agricultural sectors. The transition to green materials is supported by growing environmental awareness. The need to explore antioxidant molecules is supported by widespread availability in nature, such as lignin and polyphenol adduct polysaccharides. Additionally, certain natural essential oils such as limonene also feature antioxidant properties and can be polymerized into renewable polylimonene while preserving their antioxidant properties. The antioxidant polymers (including polyfurfuryl alcohol and its derivatives) can be directly sourced from agricultural wastes. Polyphenols drawn from a variety of sources, including fruits and vegetables, dopamine, pyrogallol, tannic acid, and green tea catechins, undergo controlled oxidation and bio-inspired polymerization, which is vital in biomedical applica-

tions. For example, quercetin (a potent antioxidant) is polymerized to encapsulate cancer treatment medicines. Recently, edible flavors such as vanillin (phenolic aldehyde) have also been polymerized into an antioxidant copolymer known as polyoxalate co-vanillyl alcohol (PVAX) for biomedical applications. Vitamin C and other poly vitamins with potent antioxidant properties can facilitate the synthesis of ADMET, acyclic diene metathesis polymerization. The procedure involves a step-growth polymerization where α, ω-diene monomer is transformed in the presence of a ruthenium catalyst.

In contrast to synthetic antioxidants, natural antioxidants are naturally occurring compounds generated by plants, fungi, bacteria, and mammals, and are environmentally benign and largely biocompatible. Additionally, natural polymers are preferred due to the diminished risk of harmful byproduct formation in the course of their use relative to synthetic antioxidants [30]. Common antioxidant polymers include essential vitamins such as retinoids, ascorbic acid, tocopherols, and polyphenolic compounds epigallocatechin gallate (EGCG), quercetin, curcumin, and resveratrol [31]. The natural antioxidants exhibit unique material properties, including the ability to scavenge reactive oxygen species, targeted delivery, and long-term functionality/reactivity [32]. Such properties are vital agricultural, textiles, cosmetics, health, and packaging industries. Future applications require the development of materials with customized properties for specialized applications.
