FRG: Synthesis, Properties, and Simulations of Semi-Flexible and Ionomer Elastomers

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Carefully tailored synthesis, new analysis of physical characterization measurements, and new computer simulation methods have been developed for the study of ideal simple networks such as those made of a flexible silicone, poly(dimethylsiloxane). This project consists of using these techniques to study elastomers of more complex structures: namely elastomers from semi-flexible chains and from ionomer chains. Poly(diethylsiloxane) networks, whose elastic chains have a stiffer backbone than the corresponding dimethylsiloxane because of their larger ethyl side groups, exhibit an intriguing amorphous-mesophase transition upon uniaxial deformation. Deuterium NMR, X-ray, and computer simulation studies are proposed to elucidate the molecular structure of the mesophase, the kinetics of the transition, and the role of the network architecture on the onset of the transition. On the other hand, recent developments in the synthesis of model ionomer chains and advances in our understanding of the properties of neutral elastomers make a systematic study of some model siloxane-based ionomer elastomers very promising. Such a study will serve as the basis for an understanding of ionomer network behavior and the synthesis of novel materials.%%%Elastomeric materials, and in particular silicone-based elastomers, find a wide range of applications in drug delivery systems, in oxygen enrichment of air by membrane separation, and as stamps in the fabrication of nano-devices, to give a few examples. This project is concerned with the synthesis and characterization of new classes of silicone elastomers based on small modification of their chemical structure. These modifications lead to new physical properties such as phase transitions in elastomers made from stiffer polymer chains and amphiphilicity) absorbance of both water and organic solvents) in elastomers from slightly charged " ionomer chains. These new materials can find applications as "smart" materials (e.g. switches and self-reinforced elastomers) and as absorbents of organic pollutants in environmental remediation.