Plasticization of Polystyrene with Copolymers Based on High Oleic Soybean Acrylic Monomer

In this work, high oleic soybean oil was used to synthesize an acrylic monomer (HOSBM), which was copolymerized with myrcene and styrene at a 90:10 wt/wt feed ratio to obtain copolymers containing myrcene (HOSBM-M) and styrene (HOSBM-S). These copolymers were employed here as macromolecular plasticizers to modify the brittle nature of polystyrene (PS). Specifically, the soy-based copolymers were added to commodity polystyrene at 5–20 wt %, and the copolymer effect on the polymer blends’ structure and behavior was studied. We report on the blends’ morphology and thermal/mechanical properties and employ thermodynamic and mechanical models to understand the interactions between the PS matrix and the HOSBM copolymer dispersed phase. Microscopy indicated that the mixed materials have a phase-separated structure composed of the PS-based matrix and the copolymer-based dispersed phase. Our thermodynamic estimations and measurement of the thermal transitions showed that the blends are partially miscible, where a fraction of PS chains migrated into the dispersed phase and the copolymer was partially situated in the PS matrix. Therefore, HOSBM-M and HOSBM-S plasticize the PS matrix, decreasing the glass transition temperature and moduli. The mechanical properties of the blends depicted a trade-off between the flexural modulus, strength, and toughness. Although the PS/HOSBM-S blends showed decreased storage/flexural moduli and strength compared to neat PS, the decline was significantly lower than that demonstrated by the HOSBM-M blends. Moreover, adding the HOSBM-S copolymer to PS at 10–15 wt % loading enhances the material’s extensibility compared to pure PS. The trend in the toughness values shows that the optimal HOSBM-S loading is 10 wt % to obtain materials with the best middle ground between flexural modulus, strength, extensibility, and toughness.