*1.5. A Review of Antioxidant Molecule-Incorporating Polymers*

The encapsulation of antioxidant molecules in conventional polymers is integral to the regulation of the potential toxicity, lability, solubility, and diffusion, and other antioxidant properties; this is particularly true for natural antioxidant polymers, which achieve high antioxidizing effectiveness at relatively low concentrations [33]. In other cases, the incorporation of antioxidant molecules into polymers has been proven useful in autosynergism and heterosynergism [33]. Lith and Ameer [32] and Sawant et al. [1] reported the successful encapsulation of vitamin C antioxidant polymer in PEO (or poly(ethylene glycol), PEG) micelles. The incorporation of vitamin C into PEG/PEO micelles was beneficial in the treatment of cancer. Preliminary in vivo experiments using mouse models demonstrated selective necrosis of breast cancer cells; the outcomes demonstrate the unique capabilities of antioxidant compounds embedded into polymers [1,32]. However, the potency of the antioxidant polymers was dependent on concentration—higher concentrations were established to be highly effective in overcoming cancer antioxidant defense mechanisms. Wang et al. [26] reported successful incorporation of paclitaxel into polyethylene glycolb-poly(D, L-lactide) (PEG-PDLLA) micelle for tumor-targeted drug delivery. Preliminary clinical data show that the technique offers promising prospects in the treatment of tumors.

Beyond targeted drug delivery, the encapsulation of antioxidant molecules in conventional polymers was proven beneficial in agricultural and food packaging applications. The incorporation of primary phenolic antioxidants into polyolefins and polyethylene has been proven useful in the protection of the thermo-oxidative stability of polymers used in packing [30]. The stabilization of synthetic polymers exposed to natural elements, including UV radiation, shear forces, and higher temperatures, is integral to their durability post-production. However, there are ecological implications associated with the incorporation of natural phenolic antioxidants into polymers [30]. Some studies have suggested that the incorporation of antioxidant polymers into polymers poses significant environmental and health hazards. For example, the study found traces of plastics (polyethylene) in drinking water [34]. The problem was attributed to the byproducts of phenolic antioxidant additives used in pipeline production [34]. The compounds migrated to waterways via diffusion. The presence of polymers in drinking water elevates the risk of health complications associated with reactive oxygen species [32]. Even though the latter findings point to the negative effects of antioxidant molecules in conventional polymers, there are tangible benefits associated with the embedding of antioxidant species. The positive benefits in the agricultural, textiles, cosmetics, health and packaging industries help to offset the adverse effects.
