High-Performance Polymers

The polymers that are found in common commercial uses, such as fibers, films, or structural resins, fail to withstand elevated temperatures above 250C for long periods of time and decompose. There is a need, however, in various technologies for materials that can tolerate temperatures over 300C for reasonably long periods. Many such materials might be too high priced for common commercial use. They find application, however, in specialized areas that include space, aeronautic, or military technologies, where a higher price is justified by greatly enhanced performance. In developing tough, heat-resistant polymers the chemists pursued several goals [191]. These were: 1. To improve heat stability of the available polymers by introducing structural modifications. 2. To develop new macromolecules based on chemical structures capable of withstanding high temperatures. 3. Because many inorganic molecules are more thermally stable than the organic ones, to develop inorganic and inorganic–organic polymeric materials. Improvement of thermal stability of existing polymers has to be based on the following considerations: (1) The primary bond energy between atoms in a polymeric chain is the greatest source of thermal stability. The strength of these bonds, therefore, imposes an upper limit on the vibrational energy that a molecule may withstand without bond ruptures. In cases of cyclic repeating units, as in ladder polymers, a rupture of one bond in a ring may not lead to loss of molecular weight. In such polymers, two bonds would have to break within the same ring for the chain to rupture, and the probability of that is low. This means that ladder polymers should exhibit greater heat stability than single-stranded chains [183]. (2) Secondary bond forces or the cohesive energies contribute additional stability to the molecule. (3) Resonance energy of aromatic and heterocyclic structures contributes an additional amount of thermal stability and bond strength. (4) Polymers with high melting or softening temperatures are generally more heat-resistant.

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مواضيع ذات صلة

Cardo Polymers

Oligomers with Terminal Functional Groups

Diels–Alder Polymers

Polyphenylene

Fluorine Containing Aromatic Polymers

Phosphonitrile Polymers

Polysilanes

Polyarylsiloxanes

Fluorosilicone Elastomers

Polysiloxane Coating Resins

Silicone Elastomers

Silicone Elastomers