Polyimide components, chemical structure

Table 13.1. Chemical Structures of Dianhydrides from Polyimides Where One or Both Monomer Components Are Fluorinated...

Figure 24.13 Chemical structure of the components of the polyimide/silica nanocomposites.

A series of 6FDA-based polyimides containing laterally attached p-terphenyls and biphenyls moiety was synthesized by Chung and co-workers [178] to investigate the effect of noncoplanar components on gas permeability and selectivity. The chemical structures of the polyimides are shown in Scheme 3.14. They observed that only p-terphenyl... 

Although Eq. (2) is not adequate to fully describe ablation processes, the absorption coefficient is still a useful parameter as it provides a quantitative evaluation of the level of interaction between a given medium and photons of a specific wavelength and, to a first-order approximation, their propensity to laser ablation. 5 different materials can have different chemical compositions and structural arrangements, it is not surprising that they have different absorption coefficients and thus can exhibit different ablation characteristics. This is indeed found to be the case. For instance, PMMA is readily structured at 193 run ( 193 2 X 10 cm I) although it is essentially transparent and unaffected at 308 nm (a 308 < 1 x 10 cm i). However, for an aromatic polyimide such as the system whose dianhydride/diamine components are pyromelletic dianhy-dride/oxydianiline (PMDA-ODA), ablation occurs readily not only at 193 nm... 

The fabrication of the material that forms when linear polyimides are mixed or coupled with epoxy resins to form three dimensional interpenetrating networks (IPN) is wrought with problems. These can be viewed from a polymer science aspect, where chemically modifying the structure of the components will result in their compatibility or from an engineering viewpoint where modifying existing fabrication methods and formulations will result in the desired composite materials. The following is a summary of research of epoxy and polyimide combinations to date. 

X-ray photoelectron spectroscopy has been used to study the metal polyimide interface formed during room temperature metal deposition. Several mono-layers of Al, Au and Cu were sputter-deposited onto cured polyimide, to a thickness which permitted the observation of both polyimide and metal peaks. Deconvolution of core-level Cls, Nls and Ols polyimide peaks and A12p, Au4f and Cu2p3/2 metal overlayer peaks has demonstrated that chemical reaction occurs at the carbonyl sites for all these metals under the conditions used. In addition, the aromatic nature of the molecular structure at the interface is believed to decrease while the percentage of an isoimide-like component increases. 

Phthalides and phthalic anhydrides are extremely common components in a huge variety of polymers, and are prepared using many chemical processes. There are over 1300 references to polymers derived from phthalic anhydrides in the Registry File of Chemical Abstracts. Phthalic anhydride itself is used in polyester resins but there are also many examples of polyimides that are derived from related anhydrides. In this section, a few examples representing a range of structure and polymerization process are presented. 

For all cured, non-modified polyimide films studied, the C Is spectra showed extremely weak satellite features centered about 292.8 0.3 eV. To date, we have not studied these shake up structures extensively. We have noted, however, that they frequently do not exist in the C Is spectra of the polyamic acid films. These low intensity features appear resolvable into two Gaussian components of unequal intensity. Their chemical shifts are consistent with assignments given to n ntransitions e.g., D.T. Clark et al, J. Electron. Spectrosc. Relat. Phenom., 51... 

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