| In this work, the relationships among structure, microdeformation processes and mechanical behavior in several different polymer blend systems were studied.; Poly(methyl methacrylate)/polyurethane blend system is discussed in Chapter 1. The goal of this project was to modify the structure and properties of polymer blends by using a reactive initiator that can enhance the adhesion between different phases in the polymer blends. This project utilized the technique of polymerizing liquid monomer that had been pregelled by another monomer to produce new polymer blends. The effects of different initiator systems on the morphology and properties of these polymer blends have been investigated. Microscopic study of the PMMA/PU blend prepared by a normal azo initiator showed that the PMMA phase existed as isolated particles poorly adhered to the PU phase. With an reactive initiator which had reactive carboxylic functional groups, the PMMA phase existed as aggregates of interconnected spheres which were tightly bound to the continuous PU phase. This difference is morphology was responsible for the change in the tensile failure mechanism by inhibition of premature crack propagation in the reactive initiator blends. This enhanced morphology in the new system resulted in greater tensile strength, increased elongation at break, and better recovery. The key finding of this study was that the chemical reactivity of the initiator system was critical in influencing the morphology and properties and these polymer blends.; Chapter 2 discusses the effect of crystallization of isotactic polystyrene on the mechanical properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and isotactic polystyrene (IPS). Miscible solution blends of PPO and IPS have been investigated as a function of composition, thermal history, and test temperature. Since IPS can be crystallized thermally while PPO cannot, it is possible to prepare IPS/PPO blends that contains a crystalline IPS phase, and an amorphous phase consisting of PPO and uncrystallized IPS. The relationships between the deformation processes and the mechanical behavior, especially the brittle to ductile or craze to shear transition, have been studied by observation of the blend films using optical microscopy, simultaneously with tensile testing. While the crystallization of the IPS component significantly improved the high temperature properties, it also made the blends more brittle. By melt blending Noryl with IPS, the toughness of blends was improved, while retaining the high mechanical properties imparted by the crystallinity. |
