Polychloroprene rubber melt temperature

Figure 15.13 Effect of polymerization temperature upon ciystalline melting temper-amre of polychloroprene rubber jxoduced by emulsion pdymmzatian (Mi nard and Mochel [26]) ( ) highest observed melting point ( ) lowest observed melting point...

The tendency for a polychloroprene rubber to crystallize increases as the polymerization temperature is reduced. This tendency is illustrated by results of Maynard and Mochel [26], given Figure 15.13, for the effect of polymerization temperature upon the melting temperature of the pol3mien as the polymetizadon temperature is reduced, so the temperature at which crystallization is able to occur increases progressively. This is believed to be primarily a consequence of die effect of temperature upon the stereoregularity of the polymer. The results shown in Table 15.6 indicate that it is probably the enhanc concentration of ds-1,4 units in polychloroprenes produced at higher temperatures which is responsible for the retardation of crystallization, rather than the presence of the 1,2 and 3,4 units. It appears that, for chloroprene homopolymers, other variables, such as molar mass and crosslink density, have little effect upon tendency to crystallize. 

Figure 9.33 (132) illustrates the application of the equation to natural rubber and polychloroprene (see Section 9.15 for structures). The equation fits the data for natural rubber somewhat better than for polychloroprene, although both polymers are fit for reasonable extensions. It must be pointed out that while the pure polymers both crystallize somewhat above room temperature, ordinary vulcanization and compounding lower the melting temperatures significantly, shifting the data in Figure 9.33 upward. Typical numerical values for equation (9.93) are as follows ... 

Using standard polymerization conditions, crystallization is an inherent property of all polychloroprene rubbers [12]. A homopolymer manufactured at 40°C has a trons-1,4-content of ca. 90%, a degree of crystallization of ca. 12%, and a crystalline melting temperature of ca. 45°C. A reduction in the rate of crystallization is possible... 

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