Structure-Property Relationships of Functionalized Polydimethylsiloxane-Based Ionic Polymers

Abstract

Ionomers exhibiting good thermal stability have been prepared by mixing 3 uncharged components—a poly(dimethyl)siloxane (PDMS) with randomly-substituted amidine or imidazoline side chains, an alkylamine, and carbon disulfide. In essence, the three uncharged components produce charged materials, polyelectrolytes with amidinium dithiocarbamate ion pairs. The preparation, structures, and properties of the ionomers at the microscopic and macroscopic levels are reported as a function of PDMS chain length, degree of amidine substitution, and length of the alkyl group of the amine component. Whereas ionomers with hexyldithiocarbamate anions are viscous liquids at room temperature, those with octadecyldithiocarbamate groups are semi-crystalline solids, exhibiting multiple thermal transitions between 0 degree celsius and the temperature at which they become isotropic phases. The structural natures of those transitions have been characterized from analyses of data from DSC, X-ray diffraction, and rheology measurements. Among the interesting properties exhibited by the ionomers are strong adhesion to different surfaces, and high ultimate shear stress considering their relatively low amidinium contents.