Optically transparent polyimides

Recently, perfluorinated polyimides have been synthesized from novel perfluorinated dianhydrides of both the fluorine and trifluoromethyl types (lOFEDA, P2FDA, P3F, P6F) along with a series of perfluoroaromatic diamines (TFPDA, 4FMPD, 8FODA, 8FSDA). These materials were shown to have superior optical transparency, reasonably high TgS, and reasonably low dielectric constants. 

Optical Transparency of Fluorinated Polyimides at Near-IR Wavelengths... 

A high optical transparency is a basic requirement for optical applications. However, conventional polyimides such as PMDA/ODA have a low optical transparency owing to their dark yellow coloration (they are semitransparent, not opaque). Colorless polyimides have been developed for use in space components, such as solar cells and thermal control systems for the first time. ... 

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." -" ... 

The fluorinated polyimides PMDA/TFDB and 6FDA/TFDB and the copolyimides have the high optical transparency, controllable refractive index. 

The internal surface of the capillaries can be uncoated, to allow the inner silica surface to be in contact with buffers and analytes, or coated (to shield the silica surface from interactions with analytes prior to filling). The external surfaces of the capillaries are coated with a layer of polyimide for flexibility. Where the capillary needs to be optically transparent to allow detection, the external coating is removed. In this window the capillary is very fragile but is transparent, even in the low UV region. When detection is carried out directly in the capillary, its effective length is from the injection end to the detection window, whereas the total length corresponds to the distance from the two ends of the capillary (Fig. 3.7). Capillaries may vary in length from 20 to 100 cm. 

Fluorinated polyimides are interesting for optical applications because they have good optical transparency. The optical transparency of polyimide films is significant in some applications such as liquid crystal display devices and optical half-wave plates for planar light wave circuits. However, most polyimides have strong absorption between ultraviolet (UV) and... 

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. 

Studies [41,47] have demonstrated that polyimides derived from ether-bridged aromatic diamines with -CF3 groups are soluble, high-temperature polymer materials with low moisture absorption, low dielectric constant, high optical transparency, and low birefringence. The effect of fluorene substitution on the dielectric constant of polyimides has been demonstrated for a broad spectrum of fluorene-containing diamine structures (Table 3.2). The... 

Aromatic polyimides are an important class of high-performance polymers with interesting properties such as good chemical and solvent resistance, high thermal and mechanical properties, and high optical transparency. These excellent properties make them suitable for engineering plastics to be used in... 

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