Inherently dissipative polymer

Electrical Properties. CeUular polymers have two important electrical appHcations (22). One takes advantage of the combination of inherent toughness and moisture resistance of polymers along with the decreased dielectric constant and dissipation factor of the foamed state to use ceUular polymers as electrical-wire insulation (97). The other combines the low dissipation factor and the rigidity of plastic foams in the constmction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (213). 

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. 

Two lower states of the frans-(CH) are energetically degenerated as follows from symmetry conditions. Theory shows that electron excitation invariably includes the lattice distortion leading to polaron or soliton formations. If polarons have analogs in the three dimensional (3D) semiconductors, the solitons are nonlinear excited states inherent only to ID systems. This excitation may travel as a solitary wave without dissipation of the energy. So the 1-D lattice defines the electronic properties of the polyacetylene and polyconjugated polymers. 

In current industrial practice, reactive processing carried out in non-isothermal conditions, for both inherent and other reasons, such as changes in temperature at the surface of an article during the process cycle. Inherent reasons are the existence of inner heat sources, which can be of chemical origin (enthalpy of reaction), heat of phase transition from crystallization of a newly formed polymer or heat dissipated due to the flow of a reactive mass. 

The principal characteristics of polymers which control their ability to dissipate energy are their stiffness, surface mass, and their inherent damping characteristics. In this chapter we are only concerned with the last of these three. Briefly, however, if lack of stiffness is a problem with a particular polymer in a damping system, this can be enhanced, if not completely obviated, by using the material in a constrained layer (29) mode. Surface mass refers to the mass of material behind a unit surface area. Clearly, for polymers which are all inherently low density materials, this can be increased by the incorporation of dense, particulate fillers such as lead, barytes etc. 

In the case of sPS, the problem of its brittleness can be even more acute since it has to compete with engineering plastics which possess an inherent toughness superior to that of sPS. For this reason, a good impact modification of this product is of paramount importance and may even be essential for its survival as a commercial thermoplastic. For this reason a chapter of this book has been dedicated to the impact modification of sPS using elastomers. Since rubber modification plays such an important role for styrene polymers, whether atactic or sydiotactic, we will first look at the methods of energy dissipation in these homopolymers on impact. 

UV absorbers absorb UV radiation and dissipate it as heat in order to avoid photosensitization of the protected polymer. The UV absorber of choice should have high absorption coefficients and high inherent light stability. Chemical structures comprise mainly benzophenones, benzotriazoles, hydroxyphenyltriazines, cinnamates, di-phenylcyanoacrylates, and oxanilides (Fig. 11.14). 

One of the advantages of polymers is its inherent dielectric property, but this can be a problem when static electricity needs to be dissipated. Antistatic agents are described in Sections 3.3.8.1 and 3.3.S.2. 

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