NSF Award
0412582
Proposed Research. The research performed during the 2001-2004 NSF grant period has demonstrated the strength of the imaging method based on electron spin resonance, ESRI, to provide spatially- and morphologically-resolved information on polymer degradation in heterophasic polymers. The systems studied were poly(acrylonitrile-butadiene-styrene) (ABS), and propylene-ethylene copolymers (HPEC), both containing a hindered amine stabilizer (HAS). The HAS-derived nitroxide radicals act as radical scavengers, and provide the contrast in ESRI experiments. But questions remain, and will be addressed in this research plan. The following major objectives are: 1. Understand the effect of irradiation wavelength in UV degradation. 2. Assess the importance of HAS structure and molecular weight, and of the local environment on the formation and consumption of HAS-derived nitroxides. 3. Map the formation and distribution of nitroxides in various domains, and evaluate the effect of the morphology on their distribution. 4. Increase the resolution in ESRI experiments by refining the software for image reconstruction. 5. Initiate an in situ study of degradation of proton exchange membranes (PEMs) in fuel cells; this is a risky part in the long-range planning described in this proposal (four years). The proposed study includes spectroscopic methods (continuous wave and pulsed ESR, FTIR, UV), and ESR imaging.<br/>Intellectual Merit. Polymer degradation and stabilization is a challenging topic of great fundamental and technological importance: Fundamental, because it reflects the change in properties of polymeric materials due to chemical phenomena that can vary as a function of environmental conditions. Technological, because the use of polymeric materials is increasing steadily, and because of the increasing sophistication required in specific applications. The ESRI method that we have developed is exceptionally sensitive to early events in the degradation process, and therefore of predictive value. Moreover, the method is nondestructive, an advantage that is particularly important for semicrystalline systems such as polypropylene-based heterogeneous and other self-assembled polymeric systems, for instance ion-containing polymers, and block copolymer micelles. The expected results of this research plan are accurate prediction of lifetimes for polymeric materials and a better understanding of environmental factors (for instance heat, light, humidity, and oxygen); these results are of great fundamental interest and crucial for industrial applications.<br/>Broader Impact. Graduate and undergraduate students, as well as postdoctoral fellows and visiting scientists are part of the research team. Although focused on specific goals, the contribution of each participant will be analyzed and shared by all, and disseminated at group seminars and meetings. International collaborations (with scientists from Japan, France, Poland, Russia, Romania, and Germany) and contact with scientists in industrial labs (Dow Chemical, Toyota, General Motors, and Giner) have developed because of the novelty of our approach to the problem of degradation, and the versatility of the ESRI method. This PI plans to develop a new unit entitled "The Science of Fuel Cells", in the Special Topics series at UDM, Chemistry 601, which will be tailored for graduate and advanced undergraduate students. This topic emerged from our studies of self-assembling of ionomers (supported by the Polymers Program), and is motivated by our recent interest in the study of PEM stability.
