Polyimides physical characteristics

Relative to what is known regarding many physical characteristics of this family of polymers, hydrolytic stability remains comparatively unexplored. Among the reasons for this low level of research activity is the difficulty of accurately determining the chemistry occuning in these traditionally insoluble compounds. Hydrolytic stability of polyimides in the solid state has been... 

Polyimides have also been the subject of many review compilations of papers and continue to be the focus of many conferences around the world [28-33]. Having various chemical forms, including isoimides, polyimides have found use in a vast array of applications that in some cases, due to their superior physical characteristics have displaced epoxies, for example, as matrix polymers in aerospace vehicles. 

Copolymerization of the Al-(hydroxyphenyl)maleimides with other monomers can produce polyimides with characteristics different from the homopolymer of either monomer. This has been utilized by Chiang and Lu , who claimed that useful physical characteristics are exhibited by the copolymer of Af-(hydroxyphenyl)maleimide with p-trimethylsilylstyrene (TMMS). Polyimide residue of the copolymer contributes... 

Chang WY, Fang TH, Lin YC (2008) Physical characteristics of polyimide films for flexible sensors. Appl Phys. A 92 693-701. 

Organic substrates consist of layers of paper impregnated with phenolic resin or layers of woven or nonwoven glass cloth impregnated with epoxy resin, polyimide, cyanate ester, BT resin, etc. The usage of these substrates depends on the physical characteristics required by the application of the PWB, such as operating temperature, frequency, or mechanical... 

Aromatic polyimides are well known for their unusual array of favorable physical properties, including excellent thermal stability and excimer-laser processing characteristics. The polyimide structure possesses lower-energy transitions such as n —> n, n —> o, n —> n, and a — n (in order of increasing energy71). However, the w — n and o —> n transitions are forbidden by symmetry rules and related absorptions are significantly weaker than those for... 

The most common advanced composites are made of thermosetting resins, such as epoxy polymers (the most popular singlematrix material), polyesters, vinyl esters, polyurethanes, polyimids, cianamids, bismaleimides, silicones, and melamine. Some of the most widely used thermoplastic polymers are polyvinyl chloride (PVC), PPE (poly[phenylene ether]), polypropylene, PEEK (poly [etheretherketone]), and ABS (acrylonitrile-butadiene-styrene). The precise matrix selected for any given product depends primarily on the physical properties desired for that product. Each type of resin has its own characteristic thermal properties (such as melting point... 

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. 

Physical properties of the polyimide films are listed in Tables I, II and III. Based on WAXD spectra and DSC results, the five polyimides were determined to be amorphous. Chemical structures and characteristics of the amorphous BPDA and 6FDA polyimide films from the previous study are shown in Figure 2, and Tables IV and V, respectively(8,9). In Table V, we present new permeability and diffusivity data at 80 C of the polyimides reported in our previous study. 

In O Sect. 12.4, the physical form of adhesives is used for classification purposes and specific adhesives are discussed for each class of adhesives to provide more insight on adhesive categories including chemical families. This is because, many adhesives have cross-category characteristics, as already illustrated with some of the above listed adhesive examples. Additional examples are epoxies, which are typically listed as structural adhesives, but are also available in elastomer-epoxy forms high-temperature thermoplastic polyimide adhesives. 

Design of the reactions via long-lived active intermediate was found to be important for developing photosensitive polyimide tystems, and this concept is especially effective for the reactions in solid state 11), because the solid-state reactions are controlled by the molecular motions 12). In addition, change in the electronic state in polymer solid was found to affect the efficient of their photoreactions. Charge-transfer structure is one of the characteristic nature of aromatic polyimides, which is affected by the change in their physical properties, and which in turn controls their photoreactivities. 

Polyimides are an important class of polymers for high temperature aerospace applications. Thin polyimide films are ideal candidates for protective coatings on antenna reflectors and other electronic applications. Their properties, both physical and electrical, are expected to be strongly influenced by their morphology. We have developed a novel technique for monitoring microstructural characteristics of thin polymer films. It is based on the sensitivity of the positron lifetimes to the molecular architecture of the polymers. Specifically, positron lifetimes can be used to calculate free volume hole radii and free volume fractions in the test polymers. A free volume model has been developed to calculate dielectric constants of thin polyimide films. It has been tested on a series of special purpose polyimide films developed for aerospace communication networks. The results are described in the following sections. 

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