This study is on the preparation of rubber toughened syndiotactic polystyrene (sPS) via reactive compatibilization. sPS is a recently developed engineering thermoplastic, synthesized using metallocene catalyst. So it has been having an attention for industrial and academic researcher because of its attractive features, high heat resistance, low dielectric constant and good chemical resistance. But its critical defect for various applications is poor impact strength. So it is essential to toughen sPS by blending with rubber components as a stress concentrator in order to widen its applications.
To modify ethylene-propylene random copolymer (EPR), maleic anhydride (MA) was melt grafted on EPR, and oxazoline containing polystyrene (RPS) was used to occur the reaction with EPR-MA during melt blending.
The reactivity between RPS and EPR-MA was examined by FT-IR characterization. FT-IR spectrum of RPS/EPR-MA blend had $3440 cm^{-1}$ N-H secondary amide peak and $1713 cm^{-1}$ carboxylic acid peak that were generated by the reaction of oxazoline/MA. These characteristic peaks did not find in the nonreactive blend of RPS/EPR.
The miscibility between RPS and sPS was investigated by the two methods; thermal (glass transition behavior and enthalpy relaxation behavior) and rheological analysis. The cold crystallization peak $(T_{cc})$ moved toward higher temperature as increasing the amount of PRS, which indicating the amorphous RPS chain hindered the crystallization of sPS. Also, the glass transition breadth maintained constantly along the various compositions, which is the evidence that the single $T_g$ peak did not come from the superposition of two sPS and RPS $T_gs$. In the enthalpy relaxation behaviors, only one single enthalpy relation peak is found in all aged samples along the various compositions. In rheological measurements, the plots of G' and G' as function of frequency, and Log G'-Log G' relationship showed almost the same slope and trend with miscible blend behavior. From these results, it could be concluded that RPS is miscible with sPS along various compositions.
In sPS/RPS/EPR-MA blends with varying the amount of RPS, the torque during the melt process increased as the addition of RPS, as a compatibilization effect of copolymer formed by the reaction of RPS/EPR-MA. Notched impact strength improved significantly, indicating that sPS was toughened by introducing the reactive agents, RPS and EPR-MA. The fracture surfaces of reactive blends after impact test, also, were evidences of the improvement of toughness of sPS; small domain, rougher fracture surface and distinct domain deformation in reactive blends comparing to nonreactive blends. For the rheological measurements, the reactive blends tended to show the increase of G' and complex viscosity. These behaviors caused from the compatibilization effect of copolymer formed during the blend process.
