Polyimide, structure

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). 

Ziegler-Natta catalysts and, 1210 Polyimide, structure of, 837 Polymer(s), 239... 

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... 

Thus, the ease of polymer synthesis, the facile handling of soluble precursors, the ready thermal or chemical conversion to the final polyimide structures, and the often unprecedented polymer properties that can be obtained collectively make polyimides highly desirable for a wide range of applications. 

Since this meta-substituted diamine was much more reactive than OFB, a variety of polyimides could be made, aUowing the synthesis of such structures as PMDA-PFMB, a polyimide with a very low thermal expansion coefficient (CTE) that may provide many advantages for microelectronic fabrication. Linear polyimide structures have generally been found to have low CTEs even when bulky groups were attached to the main chain. 

There are some overall structure-property generalizations that can be drawn from this survey. Incorporation of fluorine into polyimide structures usually has die following effects, which are elaborated in the sections below ... 

The primary purpose of incorporating fluorine into polyimide structures is to decrease the dielectric constant. Considerable effort has been devoted to the creation of new chemistry and to understanding the limits and principles behind this approach. 12.25-27,29,31-34,51-60,65,78,158 ygjygg gf (jjg dielectric constant in nonfluorinated polyimides generally range from about 3.0 to 4.0. Fluorinated polyimides generally range from about 2.6 to 3.3 (see Table 13.3). 

The first, and currently only, successful solvent-permeable hyperfiltration membrane is the Starmem series of solvent-resistant membranes developed by W.R. Grace [40]. These are asymmetric polyimide phase-inversion membranes prepared from Matrimid (Ciba-Geigy) and related materials. The Matrimid polyimide structure is extremely rigid with a Tg of 305 °C and the polymer remains glassy and unswollen even in aggressive solvents. These membranes found their first large-scale commercial use in Mobil Oil s processes to separate lube oil from methyl ethyl ketone-toluene solvent mixtures [41-43], Scarpello et al. [44] have also achieved rejections of >99 % when using these membranes to separate dissolved phase transfer catalysts (MW 600) from tetrahydrofuran and ethyl acetate solutions. 

Before implantation several in vitro tests were performed. For evaluation of a possible toxic reaction, we investigated the material and the whole devices in vitro with cell culture methods. Direct contact and extraction tests with a mouse fibroblasts cell line (L 929) and a neuroblastoma cell line (neuro-2-a) were performed according to the international standard ISO 10993 ( Biological Evaluation of Medical Devices ). The materials and devices showed no toxicity, i.e. no significant differences in membrane integrity of the cell membranes, mitochondrial activity and DNA synthesis rate. The neuro-2-a cell line is so sensitive that even small changes in process technology are detectable. The flexible polyimide structures proved to be non toxic. 

There is an excess energy at a surface, measurable as a surface tension(8.). This causes the surface layer of a curing polymer to react farther and faster than the bulk. In the case of polyimide, it also promotes some surface layer structural rearrangement (-8%) to isoimide( ), causing changes in both mechanical(10) and electrical ( ll I properties. Further, a recent IR study (12) demonstrated that the polyimide structure obtained on curing depended on the cure schedule. 

The second significant stage in the direct production of polyimide structures involves the thermal conversion of the patterned crosslinked film to the patterned polyimide film. It is important to understand how and under what condition the photo-crosslinked polyimide precursor is converted into polyimide as well as how completely. Mechanistically it is intriguing to determine wether the crosslinking fractures are split into small pieces or escape as pure hydroxyethylmethacrylate comparable to the zip-off depolymerization of polymethylmethacrylate. 

Figure 2. Process sequence for fabricating multilayer Cu/polyimide structures.

FIGURE 6. Generahzed polyimide structure, where Ar = aromatic ring... 

In addition to the polyimide structures discussed, dianhydride monomers have also been found to be useful in the preparation of polypyrroles. Reaction of dianhydrides with tetramines in polyphosphoric acid leads to these thermally stable polymers as indicated below. 

Does placement of the hinge In the polyimide structure affect wear resistance ... 

R. Petiau, N. Cornet, G. Gebel, M. Pineri, Stability study of sulfonated phthalic and naphthalenic polyimide structures in aqueous medium Polymer 42 (2001) 5097-5105. 

It was observed that the TBAPP-based polyimides derived from dianhydrides BPDA and BTDA were soluble in polar aprotic solvents. The high solubility of TBAPP-based polyimides was possibly governed by the structural modification through the incorporation of the flexible isopropylidene, increasing the overall chain flexibility, and methyl substituted arylene ether groups into the polyimide structure. It has been verified that polyimide derived from diamine DAM3 (Table 2.4) had less solubility than that derived from diamine TBAPP. This result clearly demonstrated that the tetramethyl substituents on the phenylene unit effectively improved the polymer solubility. It has been reported that methyl... 

Sulfonated polyimides (sPI) are another type of ionomers that have been prepared [5] by copolymerization of 4,4 -diamino-biphenyl 2,2 -disulphonic acid (BDSA), 4,4 -oxydianiline (ODA), and naphtalenic or phthalic anhydrides. Polyimide structures based on six-membered rings derived from naphtalenics anhydrides, such as 1,4,5,8-naphtalene tetracarboxylic dianhydride (NTDA), shown in Fig. 6.8, are more hydrolitically stable than the five-membered rings basedoxy-diphthalic anhydrides (ODPA). 

HR-602 - This system represents a different resin chemistry through use of acetylene-terminated polyimide structure. The cure mechanism consists of an addition reaction with no release of volatiles during cure. The intermediate acetylene-terminated polyimide structure is shown below. Reaction to the final cured structure is proposed as a trimerization of the acetylene groups to form an aromatic structure. 

The primary purpose of incorporating fluorine into polyimide structures is to decrease the dielectric constant. Considerable effort has been devoted to the creation of new chemistry and to understanding the limits and principles behind... 

---