High-temperature thermoplastics are melt-processable plastics. High-temperature thermoplastics have a long-term stable structure at temperatures above 150 °C, and their short-term use temperatures can be higher than 250 °C. The excellent temperature capabilities of these polymers are highly attractive in the plastics market and in recent years their market share has maintained a high growth rate. Sometimes high temperature thermoplastics are also known as "high performance plastics." Therefore, the cost of high temperature thermoplastics is on average 10 times higher than that of general purpose plastics! 
Figure 1: Degradation of aromatic and linear polymers due to heat aging
High temperature thermoplastics generally achieve their temperature resistance by introducing a rigid aromatic ring into their molecular structure rather than an aliphatic group. This limits the movement of the backbone and requires the breaking of two chemical chains (compared to one of the fatty structures) for strand breaks (Figure 1). Therefore, the mechanical properties, high temperature properties and chemical resistance of high temperature thermoplastics are greatly improved. High temperature thermoplastics generally perform better than crosslinked thermoset polymers.
Figure 1: Degradation of aromatic and linear polymers due to heat aging
In practical applications, high temperature thermoplastics often need to be compounded and modified to meet specific application properties. By using a special reinforcing material such as glass fiber, heat deformation resistance and rigidity can be further improved as compared with the base polymer. Additives such as fluorocarbon or graphite particles will significantly improve the sliding friction properties, adding conductive fillers will provide improved conductivity, and the addition of boron nitride and other thermally conductive fillers will provide good heat transfer, which is important in many high heat applications. .
Figure 2: Plastic Performance Pyramid
Currently, the high temperature melt processable thermoplastics market includes a number of polymer families, each consisting of several types of polymers. The plastics industry typically uses the terms such as "high performance", "engineered polymer" and "standard" or "commodity" plastics to describe the application of these materials. Figure 2 above illustrates the location of high performance or high temperature thermoplastics.
High temperature thermoplastics (such as all polymers) contain two molecular structures: amorphous (random ordered) and crystalline (highly ordered). For practical purposes, the thermoplastic is an amorphous polymer or a semi-crystalline polymer having amorphous and crystalline regions. One of the main differences between the two types is how they respond to temperature (see Figure 3). Both amorphous and crystalline high temperature thermoplastics are used in the automotive, aerospace, medical, and electrical/electronic industries where high performance is required.
Figure 3: Characteristics of amorphous and semi-crystalline high temperature thermoplastics
Automotive lightweighting is a topic that is often mentioned today, and high temperature plastics are often seen as a substitute for metal. Figure 4 summarizes some of the advantages and disadvantages of high temperature plastics compared to metals.
Figure 4: Advantages and disadvantages of high temperature plastics compared to metals
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