**1. Introduction**

Poly(vinyl chloride) (PVC) is one of the most commonly employed polymeric materials. It is used widely in packing materials, toys, healthcare, electric insulation, automobiles, and interior decorations, because of its high transparency, inertness, and reasonable mechanical properties [1–5]. Nonetheless, the intrinsic rigidity of PVC limits its end-user applications, because of its high glass transition temperature (*T*g, ca. 89 ◦C). Therefore, PVC is often blended commercially with various plasticizers, e.g., di-(2-ethylhexyl)phthalate (DEHP) [1]. A serious shortcoming of DEHP, however, is its leachability from PVC materials upon contact with tissues or body fluids [6,7].

Dissononyl cyclohexane-1,2-dicarboxylate (DINCH) is a promising substitute plasticizer for DEHP in PVC; it exhibits high biodegradability and low environmental persistence compared with DEHP, the result of replacing the benzene ring in DEHP with a cyclohexane ring in DINCH [1]. Nevertheless, this substitution can result in PVC/DINCH blend systems possessing thermal stability lower than that of corresponding PVC/DEHP blends. As a result, various nanofillers have been tested as plasticizers to enhance the thermal stability of PVC [8–10]. Ideally, these nanofillers would function as plasticizers, while inhibiting the degradation of the polymer and the release of HCl.

Polyhedral oligomeric silsesquioxane (POSS) derivatives are organic/inorganic hybrid materials that have been widely dispersed in polymeric matrices by taking advantage of both chemical and physical bonding interactions [11–26]. Such POSS-related polymer nanocomposites can exhibit enhanced strength, rigidity, decomposition temperature, and modulus, and decreased viscosity, flammability, and surface free energy, depending on the degree of dispersion of POSS nanoparticles in the polymeric matrix [27–31]. In the case of physical bonding, the POSS units can be dispersed through solvent-casting or melting/mixing blending approaches (i.e., without covalent bonding). Blending with POSS as a plasticizer can increase thermal decomposition temperature, enhance impact strength, and lower the value of *T*<sup>g</sup> of PVC [32–35]. Various functional groups (e.g., methacryl and ethylene glycol units) have been appended to POSS nanoparticles for incorporation into PVC matrices. Because the thermal decomposition temperature with 10 wt% loss of the ethylene glycol unit (*T*d10 = 250 ◦C) [35] is lower than that of the methacryl unit (*T*d10 = 420 ◦C) [33,34], in this study, we chose to combine methacryl-POSS (MA-POSS) nanoparticles with DINCH to use as plasticizers for a PVC matrix. The incorporation of MA-POSS in PVC reduces both the primary and secondary transition temperature. In addition, the ternary blend of PVC/MA-POSS/DOP could reduce *T*<sup>g</sup> behavior near room temperature with desirable ductile behavior. To the best of our knowledge, this paper is the first to describe the incorporation of combinations of DINCH and MA-POSS within PVC matrices. We have employed differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and tensile tests to characterize the glass transition and thermal decomposition temperatures, hydrogen bonding interactions, and mechanical properties of binary blends of PVC/MA-POSS and ternary blends of PVC/DINCH/MA-POSS.

### **2. Materials and Methods**
