Synthesis and thermal stability of hybrid fluorosilicone polymers

Aromatic hybrid fluorosilicones, such as perfluorocyclobutane aromatic polyethers, have higher thermal stability than typical polysiloxanes. While these polyethers decompose by homolytic cleavage of the oxygen-perfluorocyclobutane bond, the enhanced thermal stability of the polyethers may, in part, arise from this oxygen through the anomeric effect. To determine the effect of the ether oxygen on thermal stability, two perfluorocyclobutane aromatic units, one with and one without the oxygen, were modeled. To confirm the results experimentally, a series of hybrid fluorosilicones based on the latter were synthesized by thermocyclodimerization of 1-bromo-4-(trifluorovinyl)benzene, metal-halogen exchange, and condensation with one of 1,3-dichlorotetramethyldisiloxane; 1,7-dichlorooctamethyltetrasiloxane; or chlorine-terminated poly(dimethylsiloxane). The degradation temperature (T1%) was lower (∼240 °C) than the comparable polyethers (∼430 °C). These results demonstrate the importance of the ether oxygen to the stability of perfluorocyclobutane aromatic polyethers through a number of effects including the anomeric effect and enhancing the strength of the silicon-aromatic bond.