## 1 Introduction  
Thermoplastics are common polymers with high molecular weight, which are moldable at elevated temperatures. The physical properties of plastics can dramatically worsen below their melting point and above glass transition temperatures. Along with polyethylene, polypropylene, and polystyrene, polyvinyl chloride (PVC) is a well-known plastic with unique properties that allows for its use in several applications. PVC is produced in large quantities in both rigid and flexible forms [1]. Rigid PVC is frequently used in the production of construction materials (e.g., pipes, doors, and windows), bottles, cards, and packaging. Hence, the addition of plasticizers can reduce PVC brittleness and make it as soft as rubber. Soft PVC is used in manufacturing cable insulation, plumbing, and flooring. Pure PVC is a brittle white solid that is soluble in tetrahydrofuran (THF). The majority (80%) of PVC is produced through suspension polymerization along with 20% emulsion usage and bulk polymerizations. PVC has excellent properties and is inexpensive to produce; however, it suffers from photodegradation if exposed to sunlight for long durations and therefore, must be protected for outdoor applications [2].  
In the presence of oxygen, PVC photodegradation occurs due to ultraviolet (UV) irradiation, which leads to weathering as a result of chain scission [3]. Consequently, this results in changes to its mechanical properties and turns the PVC into brittle material. The photodegradation process starts with the production of free radicals that react with oxygen. These chain reactions involving radicals lead to changes in mechanical and physical properties. Additionally, PVC photodegradation leads to the formation of volatile by-products, such as hydrogen chloride (HCl), deformation, discoloration, and cracking [4]. PVC photodegradation is mainly caused by defects and irregularities in the polymeric chains along with the formation of hydroperoxides, double bonds, and carbonyl groups [5]. Photostabilizers can efficiently absorb UV light; thus, their addition to PVC can inhibit photodegradation. PVC additives should be non-volatile and chemically stable, have low production costs, be compatible with the polymer, and be used at a low concentration to avoid color changes [6]. In terms of toxicity and volatility, many limitations are associated with using previously developed additives, such as polychlorinated biphenyls, phthalates, phosphites, and mixed metals [7; 8]. Therefore, research has continued to synthesize and use new PVC additives to enhance photostability. Various additives have been used to overcome the problems associated with the creation of side products and small fragments from PVC when exposed to UV irradiation. Common PVC additives include aromatics [9; 10; 11; 12], polyphosphates [13; 14; 15], Schiff bases [16; 17; 18; 19; 20; 21], carbon nanotubes [22], and titanium dioxide [23; 24; 25; 26; 27], among many others [28; 29; 30].  
Compounds containing tin have unique physical and chemical properties and are widely used in the pharmaceutical industry [31]. Organotin compounds containing carboxylate moiety showed potential for use as a cancer chemotherapy drug [32]. They can be used as antimicrobials [33], anti-inflammatory agents [34], antitubercular agents [35], biocides and wood preservatives [36], and catalysts [37]. The biological performance of organotin compounds is dependent on the nature of organic units and the number and types of substituents (alkyl or aryl) present [38]. We recently successfully synthesized various organotin complexes and investigated their uses as PVC photod stabilizers [39; 40; 41; 42; 43; 44; 45; 46; 47]. Continuing our interest in the polymer photod stabilization subject, we can now report the successful synthesis of different tin complexes containing the prefenamic unit and their effect in enhancing the PVC photod stabilization.