Other High-Temperature Thermoplastics

High-temperature thermoplastics, such as polysulfone, polyether sulfone, polyphenylene sulfide, polyether imide, polyaryl ether ketone, and polyphenylene ether are processed at high temperatures (some above 300 °C). Here, the limit of pyrolysis is almost reached. Degradation and cross-linking as well as discoloration can occur thermal-oxidative and thermal-mechanical degradation under processing conditions have not been sufficiently investigated [38]. 

Polyurethanes are manufactured by addition of polyols (polyether or polyester) with polyvalent isocyanates. Polyether-polyols are sensitive to oxygen. Thermal-oxidative degradation typically occurs during the manufacture of flexible foams when water is used to form carbon dioxide as blowing agent. Large PUR slab stock 

100 Parts triol 105 Parts diisocyanate 4.8 Parts water 

Temperature development within a poiyurethane slab stock foam (2 x 1 x5m, density 21 kg/m ) 

These temperatures are valid only for the manufacture of PUR slab stock foams because of the large surfaces and volumes. Thermoplastic polyurethanes (TPU) are manufactured and processed - without core combustion - at temperatures up to approx. 240 °C, depending on their hardness. 

---

Polyaryl ether ketones are resistant to almost all organic and inorganic liquids at room temperature. The only exceptions are sulfuric acid and some strongly oxidizing media, such as fuming nitric acid. Even at elevated temperature, the chemical resistance of this class of products is superior to that of other high-temperature thermoplastics. Hairline cracks are formed in acetone [723]. 

Phenylquinoxalines - Polyphenylquinoxalines (PPQ) prepared from the reaction of aromatic bi s (o-di amines) and aromatic bis (phenyl-ot-diketones) are high temperature thermoplastics. They are process-able with little or no volatile evolution at relatively high temperatures (> 316°C) and pressure (-1.38 MPa) by virtue of their thermoplasticity. Like other thermoplastics, the processability is governed primarily by the chemical structure, molecular weight and molecular weight distribution. 

The primary resin of interest is epoxy. Carbon-fiber-epoxy composites represent about 90% of CFRP production. The attractions of epoxy resins are that they polymerize without the generation of condensation products that can cause porosity, they exhibit little volumetric shrinkage during cure which reduces internal stresses, and they are resistant to most chemical environments. Other matrix resins of interest for carbon fibers include the thermosetting phenolics, polyimides, and polybismaleimides, as well as high-temperature thermoplastics such as polyether ether ketone (PEEK), polyethersulfone (PES), and polyphenylene sulfide. 

For many years prior to the development of high-temperature thermoplastics and thermosets, such as the polyimides. polysulfones, and epoxies, phenolic molding material dominated the high temperature-resistant market. This emphasizes their ability to resist temperature degradation in the 400-500°F (204-260 C) range. Because phenolics were found to possess excellent ablative properties, it has been reported that both the American and Soviet space efforts used them in combination with certain other... 

In Table 1, the moisture uptake of cured and uncured Navy P3-2300-PE resin after 24 hours of immersion is compared to a number of other high-temperature polymer resins. The moisture uptake of the Navy P3 oligomer is nearly identical to that of the commercial P3 thermoplastic. Other commercial thermoplastics, such as poly(ether ether ketone), with very similar chemical compositions, exhibit similarly low levels of moisture uptake. On the other hand, the Navy P3 resins absorbs about 85% less water than the commercial polyimide Kapton HN. Since thermosetting phenyl ethynyl end-capped polyimides have moisture uptake characteristics that are similar to Kapton HN, with around 3% weight gain on exposure to 95% relative humidity (77), void-free composites based on Navy P3 resins should exhibit greatly reduced moisture uptake compared to those based on thermosetting polyimides. 

PT, 5-phenyltetrazole. Efficient, decomposes at 460°-480°F (238°-249°C). Decomposition gases are almost all nitrogen. Used with ABS, nylon, PC, thermoplastic polyester, and other high-temperature resistant plastics. 

Conventional solder procedures require the use of high-temperature thermoplastics. Other plastics can be processed using low-melting-point solders, conductive adhesives, or selective soldering methods. Available assembly and interconnection technologies as well as processes for the production of the circuit carriers must be carefully considered, selected, and possibly modified to the specific MID materials. 

Some examples of both types of plastics material are given in Table 1.1. Note that polyimides are unusual since the ones made by the addition polymerization process are thermosetting resins, but others are formally thermoplastics the difference depends on their detailed synthesis and structure. Very high temperature thermoplastics are not easily processed by conventional thermoplastics methods. 

PLCs have been shown to nucleate systems which are hard to crystallize by any other means. Polyethersulfone (PES) is a high temperature thermoplastic which, even when cast from solution, is unable to crystallize [84], as opposed to, for example, PC. However, when solution blended with 30 wt% wholly aromatic longitudinal PLC (structure not reported), spherulites of the PES can be formed and it is suggested that the combined effect of solvent molecules to lubricate the motion of the crystallizing PES molecules and a nucleant (PLC) is required, either condition on its own not being sufficient. Similar attempts to crystallize the blend from the melt failed. 

POSS exhibits several secondary effects which, when combined with primary or other secondary effects, can lead to commercial adoption. Thus, one may decide to use POSS for a primary benefit such as flow enhancement in a high temperature thermoplastic and see additional benefits such as improved mold-release, lower part friction [16,17], and better surface finish. Another known benefit is flame retardance. POSS does not provide stand-alone flame retardance but it has been reported to be an effective synergist when used in conjunction with primary flame retardants. Under combustion conditions, the POSS vitrifies [18] to form a char that provides some intumescent flame inhibition (Chapter 17). 

Polyarylate polymer properties can be tailored by compositional variation, alloying with other high performance thermoplastics, and reinforcement. This flexibility renders polyarylate one of the more versatile high temperature polymers for current and emerging markets served by engineering thermoplastics. 

The major disadvantage of teflon is its high cost (approximately 20 to 30 times greater than FR4 laminate) however, no material is currently available which can compete with it for exacting microwave applications. Some of the high temperature thermoplastics described in the next section can be used in its place for the fabrication of high-frequency substrates. Other applications of fluorinated polymers are discussed in Chapter 10. 

High-temperature thermoplastics such as polyarylate, polyketone, polysulfide, polysulfone, and thermoplastic polyimide have inherently good resistance to thermal-oxidative conditions however, stabilization against UV-light is often required. The principles described earlier for other thermoplastics also apply to the stabilization of these plastics. 

Increasing temperature requirements under-the-bonnet has led to PPS replacing other plastics such as polyamide. Also, the share of diesel engines is increasing which is further encouraging growth in high temperature thermoplastics such as PPS at the expense of other plastics. 

Nowhere is that fact more apparent than in blends of liquid crystal polymers (LCPs) with other thermoplastic polymers. It is not the intent of the present chapter to completely review all the work done in the area of blends which contain LCPs. Instead, that will be the focus of Chapter 5. The objective of the present discussion is to make general observations and show how those general phenomena may be applicable to other high temperature polymer blends as well. 

---