Thermally Stable Adhesives

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

In most cases, the allophanate reaction is an undesirable side reaction that can cause problems, such as high-viscosity urethane prepolymers, lower pot lives of curing hot-melt adhesives, or poor shelf lives of certain urethane adhesives. The allophanate reaction may, however, produce some benefits in urethane structural adhesives, e.g., additional crosslinking, additional modulus, and resistance to creep. The same may be said about the biuret reaction, i.e., the reaction product of a substituted urea linkage with isocyanate. The allophanate and biuret linkages are not usually as thermally stable as urethane linkages [8]. 

As already mentioned, aromatie polymers are thermally stable but aliphatic portions of them are not as thermally stable. Typical maleimide resins have aliphatic units. This is inevitable because the Michael addition was used to prepare the maleimide-based oligomers. On the other hand, if an adhesive consists of a linear thermoplastic polymer, it is not usable at temperatures above its softening temperature. Introdueing chemical crosslinking is one way to prevent thermal weakening of a material. 

As previously stated, the rigid polyimides meet many of the requirements for microelectronics applications however, the presence of an ordered morphology, coupled with the lack of a softening transition results in extremely poor self-adhesion. Alternatively, thermally stable thermoplastics exhibit excellent self-adhesion, but often lack sufficiently high temperature dimensional stability and/or solubility and processability from common organic solvents. For instance, po-ly(phenylquinoxaline) (PPQ) has a T in the 370 °C range, thereby overcoming... 

C. Thermally Stable Adhesives a. Polyvinyl alcohol/ester copolymers... 

Three isocyanate groups can react to form a trimer or substituted isocyanurate ring. Phosphines or bases such as sodium acetate or sodium formate can catalyze this reaction. The isocyanurate ring is thermally stable, has good chemical resistance, and can enhance the resistance of a urethane adhesive to aggressive environments. 

Anderson, G. J. and Zimmel, J. M., Thermally Stable Hot Melt Moisture-cure Polyurethane Adhesive Composition, U.S. Patent No. 5,939,499, 1999. 

The values are within the limits for electronic application. The seal is thermally stable up to 180 °C. The investigations show that by tailoring chemical structures of sol-gel derived organically modified hetero polysiloxanes, mechanical and adhesive structures can be tailored for needs of application. 

Several new developments in silanes have been reported re cently. One deficiency of existing silanes was that they were not applicable to high-temperature polymers such as polyimides, either because they were not thermally stable or because they did not facilitate adhesion. A new aromatic imide silane was synthesized with two silane groups attached to the terminal phenyls in the molecule. A... 

By reaction of phosphorylated materials with aldehydes, amines or with isocyanates highly thermally stable products have been then produced. TGA studies have indicated their superior properties compared to conventional cardanol/formaldehyde resins of the novolac type. It was also found that a phosphorylated CNSL polymer had improved adhesive properties when compared with conventional CNSUformaldehyde resins (ref.248) and certain compounded products had wear, fade and frictional properties comparable to those of conventional PhOH/formaldehyde/copolymer brake Hnings (ref.249). The phosphorylated product from CNSL and its bromination derivative possessed good fire-retardant characteristics (ref. 250). Phosphorus derivatives of cardanol and of 3-pentadecylphenol have been studied by reaction with phosphorus oxychloride and its thio analogue (ref. 251). 

In the case of dynamic random access memory (DRAM), the top electrode used in capacitor for a device s high speed raises the necessity of noble mefals like rufhenium (Ru), platinum (Pt), and iridium (Ir), which have low electric resistance and are mechanically and thermally stable. These noble metals are also chemically very stable and it is not easy to form capacitors by fhe efch back process. That is why noble metal CMP is compulsory. However, Ru is divided during the CMP process as a consequence of poor adhesion of leakage of cap oxide, grain growth of Ru, and cap oxide. To protect this phenomenon, the application of new functional slurry is essential. 

It is critical that the adhesive is formulated to take these cyclical stresses into account and tested to verify efficacy. Figure 1 illustrates the stresses created when one substrate has a higher thermal expansion coefficient. In the illustration, substrate 1 is the more thermally stable substrate (composite), and substrate 2 has the higher coefficient of thermal expansion, resulting in a higher degree of expansion or contraction. 

Features Water-based exc. adhesion to substrates, chem. and thermally stable high lubricity... 

Uses Fungicide for control of mildew on adhesive films, interior/exterior paint films, paper and paperboard prods, (for nonfood use such as soap wrappers), hard surfaces, and natural and syn. fibers such as canvas textiles and nylon carpets Features Thermally stable Regulatory EPA reg. no. 10455-30 Properties Vise, flowable liq. sp.gr. 1.15 50% act. 

Uses Biocide, slimicide, preservative for use in water treatment, paper, antifoulant paint, surf, coatings, adhesives, drilling muds, leather, timber presenration food-contact paper food-contact slimicide Features Thermally stable to 80 C nonoxidizing requires formulation in a solv. 

Ahn, B.K., Kraft, S., Wang, D. and Sun, X.S. (2011) Thermally stable, transparent, pressure-sensitive adhesives from epoxidized and dihydroxyl soybean oU. Biomacromolecules, 12(5), 1839-1843. 

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