High-temperature polymers, desirable

Organic polymers have been used to increase the viscosity of acids. The primary application is in fracture acidizing. Binary and ternary acrylamide copolymers are the most commonly used chemicals for this application. Many of these polymers degrade rapidly in strong acids at temperatures >130 F development of more stable polymers suitable for high temperatures is desirable. Recently developed polymers for this application include acrylamide copolymers with ... 

Early research on high temperature polymers concentrated primarily on thermal stability and paid little attention to their processability and cost. However, for a polymer to be successful as a c< miercially viable structural matrix, it must exhibit a favorable combination of processability, performance characteristics, and price. In particular, a desirable high temperature polymeric system for coatings, composites, and adhesives applications must exhibit adaptability to conventional processing techniques at low temperature and pressure, should exhibit good mechanical properties, acceptable repairability, weatherability, and cost effectiveness. 

Most high temperature polymers are amorphous in nature but several are semicrystalline. In the case of semicrystalline polymers, polymers with melting points that are less than about 400 °C are desirable. Above that temperature, degradation becomes significant and can become a competitive process with the melting. 

Much of the work that has been done up to this point on high temperature polymer blends is the definition of miscible blend polymer pairs and an understanding of the features that lead to that miscibility. The development of miscible blends often leads to the ability to tailor the properties, including the Tg of mixtures. Such a tailoring is an alternative to the development of entirely new polymeric materials with the desired property profile. One of the advantages of the blend approach is that it is generally faster and less expensive than the synthesis and scale-up of an entirely new polymer. The downside of the blend approach is that it is difficult to define miscible pairs and miscibility is often the situation that is not observed with polymer mixtures. 

The most significant problem in high temperature polymer applications is clearly one of processing. The characteristics which enable these polymers to perform at elevated temperatures limit their solubility and fusibility, and thus their processibility. The materials must exhibit moderate glass transition temperatures, desirable solubility-fusibility characteristics and cure via addition reactions, all of which would facilitate their fabrication as adhesives and fiber reinforced composites. 

Pol5dmides are known as reliable high temperature polymers with superior mechanical and electrical properties. Polyimides can be easily prepared by reactions between dianhydrides and diamines, and many types of polyimides have been prepared by structural modification of the monomers to obtain the polyimides having desirable... 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

The presence of the either linkages is sufficient to allow the material to be melt processed, whilst the polymer retains many of the desirable characteristics of polyimides. As a consequence the material has gained rapid acceptance as a high-temperature engineering thermoplastics material competitive with the poly-sulphones, poly(phenylene sulphides) and polyketones. They exhibit the following key characteristics ... 

The presence of ether linkages in the polymer molecule imparts chain flexibility, lowers glass transition temperature, and enhances solubility while maintaining the desired high temperature characteristics [192]. Recently, polyether imines were prepared by the reaction of different diamines with 4,4 -[l,4-phenylene bis(oxy)] bisbenzaldehyde [184]. The polymers synthesized by the solution method were yellow to white in color and had inherent viscosities up to 0.59 dl/g in concentrated H2SO4. Some of these polyimines can be considered as... 

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