High temperature performance

Because the chemical stmcture of poly(phenylene sulfide) [9016-75-5] (PPS) does not fall into any of the standard polymer classes, the Federal Trade Commission granted the fiber the new generic name of Sulfar. The fiber has excellent chemical and high temperature performance properties (see... 

Polymers based on trimellitic anhydride are widely used in premium electromagnetic wire enamels requiring high temperature performance. Several types of trimellitic anhydride-derived polymers are used as wire enamels poly(amide—imide)s (133), poly(ester—imide)s (134), and poly(amide—imide— ester)s (135). Excellent performance characteristics are imparted by trimellitic anhydride-based polymers for wire enamel requirements of flexibiUty, snap, burnout, scrap resistance, heat shock, and dielectric strength. 

Ester plasticizers are used mainly in very polar elastomers, such as neoprene and nitrile mbber, to improve low or high temperature performance or impart particular oil or solvent resistance to a compound 5—40 parts are commonly used (see Plasticizers). Resins and tars are added to impart tack, soften the compound, improve flow, and in some cases improve filler wetting out, as is the case with organic resins in mineral-filled SBR. Resinous substances are also used as processing agents for homogenizing elastomer blends. 

Differences among the processes have a major impact on the use of the products. Products from a particular process or manufacturer may dominate one market, while products from a different process may be preferred in a different appHcation. Major uses include hot-melt adhesives for appHcations requiring high temperature performance, additives to improve the processing of plastics, sHp and mb additives for inks and paints, and cosmetic appHcations. 

AppHcations for hydrogenated nitnle mbber ate similar to those of nitnle mbber in that they take advantage of the exceUent chemical and oil resistance of the polymer. However, the increased high temperature performance of the hydrogenated nitnle mbber makes it fat superior to standard grades of nitnle mbber. Examples of appHcations for hydrogenated nitnle mbber ate shown in Table 7 (27,28). 

Most types of PSAs have found some application in the label industry. Block copolymer-based adhesives are perhaps the most popular because of their high adhesion to a variety of surfaces, their low cost, their good performance over a range of temperatures and peel rates, and their ease of processing. For applications where high temperature performance is required, block copolymers have been formulated with high T end block associating resins or polymers. 

In recent years a whole new generation of high performance engineering plastics have become commercially available. These offer properties far superior to anything available so far, particularly in regard to high temperature performance, and they open the door to completely new types of application for plastics. 

Heat resistant resin compositions based on BMI/aminophenol-Epoxy blends are achieved by reacting a BMI/p-aminophenol 1 1 adduct with epoxy resin (62). Both the secondary amine and phenol functionality may react with the epoxy resin and subsequently cure through an imidazole catalyst. Imidazole catalysts promote both the epoxy/phenol reaction and the anionic maleimide crosslinking. The formation of a 1 2 BMI/aminophenol adduct, as in Fig. 20, is claimed in a patent (63). The hydroxy terminated BMI/aminophenol adduct is an advantageous curing agent for epoxy resins when high temperature performance is desired. 

With an excess isocyanate in the above systems, allophanate and biuret reactions take place (Eqs (2.25) and (2.26)), resulting in further cross-linking. When increased rigidity and high-temperature performance are desired, further crosslinking may be accomplished via isocyanurate formation (Eq. (2.29)). Base catalysts such as alkoxides, quaternary ammonium or phosphonium, etc., promote this reaction. Aromatic isocyanates give iso-cyanurates far more easily than aliphatic ones. 

The major limitation of rubber toughening of thermosets results from the fact that the increase in toughness can be achieved only at the expense of high-temperature performance or of mechanical properties, e.g., a decrease in modulus and yield stress. This can be unacceptable for structural and long-term applications (see Fig. 13.7). A second limitation is the lack of significant success in the toughening of high-Tg networks (see Fig. 13.8). 

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