Diene type polymers melting temperatures

The polymer consists of 56% by weight of chlorine. The chlorine atom has a relatively weak bond to the polymer chain. At temperatures above 280°C plastic decomposes virtually spontaneously and the chlorine atom is liberated from the main chain. At temperatures of 350°C this process may take place in seconds - for example in suitable screw mixers. Fig. 1 shows a thermogram of a melt of PVC mixed with polyolefins. The spontaneous decomposition of PVC at 280°C is clearly evident from the sharp drop downwards in the upper curves. It produces a diene - type of a polymer which degrades at temperatures above 400°C to produce certain amount of carbon. 

In the other type, termed isodimorphism, the system consists of two different crystalline structures. The formation of one or the other depends on the sequence distribution (composition) of the crystalline phase. Examples of these types of replacements are found in virtually all types of copolymer, including copolyamides [97-103], synthetic and natural copolyesters [89, 90, 104-107], vinyl copolymers [29,94, 108, 109], diene polymers [110], poly(olefins) [111-114], poly(aryl ether ether ketones) [115], andpoly(phenyls) [116]. A detailed summary of other copolymers in which co-crystallization occurs can be found in [117]. There appear to be two underlying principles that govern isomorphic replacement [117]. These are that the two repeating units should have the same shape and volume and that the new ordered chain conformation be compatible with both types. In many of these examples the melting temperatures are essentially a linear function of the composition, whereas in others there is a smooth monotonic change. 

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