High temperature polymers thermoplastic

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 ... 

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. 

Poly(aryl ketones) (PEEK, PEK, and PEKK) are commercial high temperature polymers offering an excellent combination of properties combined with thermoplastic behavior. Poly(aryl ether ketone) PAEK blends have been reviewed by Harris and Robeson [1989]. Miscibility with PEI (Ultem 1000 GE) and other PI containing isopropylidene bridging units was noted. Arzak et al. [1997] reviewed the performance ofPEEK/PEI blends and noted a synergistic behavior in ductility and impact strength as reported earlier. Utility of these blends as a thermoplastic matrix candidate for advanced composites has been proposed [Harris and Robeson, 1989 Davis et al., 1992]. 

Polyether sulfone is a high-temperature engineering thermoplastic with the combined characteristics of high thermal stability and mechanical strength. It is a linear polymer with the following structure ... 

Ladder polymers. A type of high-temperature polymer. Double linear chains of the macromolecules are periodically linked together (Fig. 1.1). They are insoluble and infusible, being unsuitable for thermoplastic processing and thus are limited in applications. In the macromolecules of step-ladder polymers shorter units of cross-linked double linear chains (ladder structures) are joined by single bonds (Fig. 1.2). An example of a step-ladder polymer is polyimide. 

The heat release rates for thermoplastics with glass fibers and charring-type thermoplastics, high-temperature polymers, and halogenated polymers from the Cone Calorimeter (Table 11.10) are in the range predicted for the burning of solid polymers and similar to those from the Fire Propagation Apparatus (Table 11.9). 

This approach was further explored by Hakemi (2000) who prepared blends that contain both a wholly aromatic and an aromatic-aliphatic LCP that are miscible with each other. The ultimate goal of this approach was to develop multi-component blends that have components of thermoplastics. The miscible LCP blends could be useful as reinforcing agents for the thermoplastic matrix polymer and, due to the fact that the LCP s contain some of the components of the thermoplastic polymer, there is expected to be improved adhesion between the LCP portion and the matrix portion of the mixture. This is another example of an attempt to balance the phase separation that is inherent in high temperature polymer blends due to molecular conformation differences by strengthening the enthalpic interaction between the two polymers. 

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. 

Bakelite was a thermoset that is, it did not flow after the synthesis was complete (20). The first synthetic thermoplastics, materials that could flow on heating, were poly(vinyl chloride), poly(styrene-5t t-butadiene), polystyrene, and polyamide 66 see Table 1.8 (20). Other breakthrough polymers have included the very high modulus aromatic polyamides, known as Kevlar (see Section 7.4), and a host of high temperature polymers. 

Figure 19.4a shows examples for thermogra-vimetric analysis (TGA) analysis for state-of-the-art HT-PEM plates of type BPP4 and low temperature LT-PEM materials as a reference. Recently developed HT-PEM materials with high temperature resistant thermoplastic binder polymers (PPS and PSU Ultrason ) are shown in Fig. 19.4b. 

Improving mechanical properties such as toughness usually serve as the main reasons for the development of novel thermoplastic alloys and blends [4]. Other reasons for blending two or more polymers together include (i) to improve the polymer s processability, especially for the high-temperature polyaromatic thermoplastics (ii) to enhance the physical and mechanical properties of the blend, making them more desirable than those of the individual polymers in the blend and (iii) to meet the market force (cost dilution). Most products succeed because of a beneficial combination or balance of properties rather than because of any single characteristic. In addition, a material must have a favorable benefit-to-cost relation if it is to be selected over other materials for a particular application. One key technical issue is whether the blend will exhibit additive properties, or not. In many cases properties are well below additive, while in others they may be above additivity. The property relationships exhibited by blends depend critically on the correct control of their phase behavior [3]. 

Polyether imide. see High-temperature polymers Polyether sulfone. see High-temperature polymers Polyethylene terephthalate. see Polyester, thermoplastic... 

An interesting PI which is not a high temperature polymer is shown in structure 7. This material deserved mention because it provided the highest average strength at 25 C for Ti TSS of any known oiganic adhesive. Strengths at 7850 psi at 25 C, 5400 psi at 93 C and 4045 psi at 121 C were reported. The PI has a Tg of 155 C, which permitted the fabrication of TSS from essentially volatile-free adhesive tape at 260 C under 100 psi. The polymer was fabricated as a thermoplastic where the time at temperature was relatively short (< 15 minutes). 

This chapter has provided a general summary of fatigue concepts, measurement techniques or methods, data presentation, and theory. It was meant to be introductory only and additional details should be obtained from the literature cited in this chapter [24-26], Chapters Styrenic Plastics, Polyether Plastics, Polyester Plastics, Polyimide Plastics, Polyamide Plastics (Nylons), Polyolefins and Acrylics, Thermoplastic Elastomers, Fluoropolymers, High-Temperature Polymers contain hundreds of plots of fatigue-related data on hundreds of different plastics. 

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