Thermal degradation, linear polymer

It has already been shown (e.g. Chapters 20 and 21) that the insertion of a p-phenylene into the main chain of a linear polymer increased the chain stiffness and raised the heat distortion temperature. In many instances it also improved the resistance to thermal degradation. One of the first polymers to exploit this concept commercially was poly(ethylene terephthalate) but it was developed more with the polycarbonates, polysulphone, poly(phenylene sulphides) and aromatic polyketones. 

Upon heating, the linear polymer synthesized from a di-N-cyanourea compound was concluded to undergo a thermal degradation of the urea linkage, as shown in Equation 7. 

As discussed in Chapter 10, network polymers - as linear polymers - obey the time-temperature equivalence principle in the domain where they are stable, both chemically (no postcure, no thermal degradation), and physically (no orientation relaxation, water desorption, physical aging, etc.). 

The examples of PA 6 and 6.6 illustrate the challenges that these polymers create. The classical research into the thermal degradation occurred during the 1950-1970 period, and extensive reviews of this work include those by Kohan25 and Peters and Still.26 Essentially, for all linear, aliphatic polyamides, thermal degradation is influenced by two major factors ... 

Although the concepts outlined in this chapter are particularly appropriate for the interpretation of hydrolytic deterioration of cellulose, they show promise as an aid in the interpretation of thermal, photochemical, photolytic, and enzymatic degradation as well. Equations 3 and 4 are generally applicable to the scissioning process in linear polymers (33, 34). 

Properties A linear polymer extremely resistant to chemicals and to thermal degradation at molding and extrusion temperature, d 1.4, self-extinguishing, dimensionally stable, very low water absorption, outstanding chemical resistance. Natural, black, or olive-green molding powder. Finely divided powder for coatings. 

During polymer decomposition, whenever a species is formed with a molecular weight not equal to that of a pseudocomponent, its amount is linearly distributed between the adjacent bins (Bi,Bi+. This lumping procedure or discrete section method was successfully applied to the thermal degradation of PS (Faravelli et al., 2001). 

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