Fluorinated polyimides properties

Recently, much progress has been made in fine-tuning the properties of fluorinated polyimides by copolymerization. Serious property conflicts, such as the countertrends of the desirable decrease in dielectric constant with fluorine incorporation and the undesirable increase in CTE have been significantly resolved by judicious choice of comonomers and their ratios. 

Fluorinated polyimides have been made with a broad range of chemical structures and possess an equally wide range of properties. Their value as low-dielectric, hydrophobic, and thermally stable materials is now well established in industry, and work continues to try to further understand underlying principles of structure-property relationships. 

These characteristics show that perfluorinated polyimides are promising materials for waveguides in integrated optics and optical interconnect technology. The thermal, mechanical, and optical properties of perfluorinated polyimides can be controlled by copolymerization in the same manner as partially fluorinated polyimides. ... 

Synthesis and Properties of Partially Fluorinated Polyimides for Optical Applications... 

This chapter describes the synthesis of partially fluorinated polyimides for optical teleconununications applications," " 2 their optical transparency (optical loss), refractive index, and birefringence properties" in addition to their fundamental properties. It also describes their device application as optical interference filters," " optical waveplates," and optical waveguides." -" ... 

This excellent balance of properties has made fluorinated polyimides very attractive for some applications in advanced technologies, for instance... 

C. Joly, D. Le Cerf, C. Chappey, D. Langevin, G. Muller, Residual solvent effect on the permeation properties of fluorinated polyimide films, Sep. Purif. TechrwL, 16, 47-54 (1999). 

Among various strategies that have been used to synthesize polyimides with lower dielectric constants, the most common approach is to incorporate fluorene, in the form of trifluoromethyl groups, into diamine and dianhydride units that minimize polarizability and increase the free volume [46]. It is well-known that fluorene atom has unique characteristics such as high electronegativity and low electric polarity. These properties give fluorinated polymers (e.g., poly[tetrafluoroethylene]) attractive features such as low water uptake, water and oil repellency, low permittivity, low refractive indices, resistance to wear and abrasion, and thermal and chemical stability. Fluorination is also known to enhance solubility and optical transparency and to lower the moisture absorption of polyimides. Therefore, it is expected that fluorinated polyimides will be widely applied in the electro-optical and semiconductor industries. The polymer series studied was essentially limited mainly to 6F dianhydride because it proved to be the only dianhydride with which many of the fluorinated diamines would form polymer films suitable for physical characterization. 

---