Polyphosphazenes and Cyclotriphosphazenes with Propeller-like Tetraphenylethyleneoxy Side Groups: Tuning Mechanical and Optoelectronic Properties

A new class of polyphosphazene elastomers has been synthesized that combines a P=N- backbone with both 2,2,2-trifluoroethoxy and tetraphenylethyleneoxy (TPEO) side groups. The polymer syntheses and photoproperties were first modeled using small molecule cyclic phosphazenes, and these were then applied to the high polymers. The TPEO groups confer useful mechanical and photophysical properties on the polymers. Thus, those polyphosphazenes with the more rigid bidentate TPEO side groups have higher fluorescence quantum yields than counterparts with monodentate TPEO groups. Different TPEO substituents also allow tuning of the side-group interactions to modify the elastomeric properties of the polymers. For example, the two-dimensional TPEO unit is a stronger physical cross-linker than the comparable cross-linkers used in earlier polyphosphazene elastomers. Thus, the elastomeric polymers containing the two-dimensional TPEO exhibit greatly improved mechanical properties compared to the previous ones. Moreover, hybrid materials that combine the new elastomers with single-walled carbon nanotubes (SWNTs) allow the fabrication of stretchable electronics with mechanically responsive properties.