Experimental results random type copolymers

4 Experimental results random type copolymers 5.4.1 Course of fusion 

Despite the lack of quantitative agreement between theory and experiment, much of which can be attributed to experimental shortcomings and inaccessibility of the very long sequences, the data in Figs. 5.2 and 5.3 qualitatively show all of the major characteristics of the theoretical fusion curves. They can be expected to be typical of the fusion of random type copolymers, irrespective of the chemical nature and structure of the noncrystallizing chain units. Random ethylene copolymers, prepared by a completely different method, display similar fusion characteristics.(21) It is important, however, to assess the generality of the conclusions with other copolymers, rather than just depending on the results of ethylene copolymers. 

The fusion curves are qualitatively similar to those shown in Fig. 5.3 for the ethylene copolymers. The melting of the homopolymer is relatively sharp. As the capryllactam concentration increases the level of crystallinity progressively decreases and the melting range broadens considerably. The experimental results that are illustrated in Figs. 5.3 and 5.4 indicate a universal pattern for the melting of random copolymers that is in accord with theoretical expectation. 

Diene type polymers, prepared by either free radical or anionic methods, contain chain units that although chemically identical are isomeric to one another. Hence, from a crystallization point of view this class of polymers behave as copolymers. For example, polymers prepared from the 1,3-dienes are subject to several different kinds of chain irregularities. For poly (butadiene), the following structures are known to exist  

Poly (butadienes), as well as other poly(dienes), can be prepared that contain an adequate concentration of cis-1,4 units so that the crystallization of this species can take place. The melting behavior of these polymers is similar to when the trans-1,4 units are the crystallizing isomer.(28) Although the melting temperatures are quite different the nature of the fusion process and the diffuse melting are typically copolymeric in character. 

---

Experimental results clearly indicate that stereo-irregular polymers do indeed crystalhze as though they were copolymers. For example, specific volume-temperature curves for isotactic poly(propylene) display all the characteristics expected for a random type copolymer. The results of such a study by Newman (44)... 

---