Effect of Polymerization Temperature

Fig. 2. Effect of polymerization temperature on the crystalline melting point of chloroprene mbbers produced by emulsion polymerization ...

All these effects increase the overall polymerization rate and decrease the degree of polymerization. The effect of polymerization temperature on the variation of monomer conversion with the polymerization time is exemplified in Fig. 8 for the emulsion polymerization of styrene. 

Figure 2. Effect of polymerization temperature (0) and AlR, Nd(vers), molar ratio (O) on molecular weight. Et,Al/ Ndivers), molar ratio was kept at 40 1 when the temperature was varied, and the temperature was maintained at 60°C when Et,Al/Nd(vers), molar ratio was varied. Nd(vers), is the neodymium salt of Versatic 10, which is a mixture of isomeric tertiary carboxylic acids.

The effect of the type and level of initiator on polymerization time, monomer conversion, and polymer molecular weight, the effect of polymerization temperature on the crystallization behavior of the polyamide generated, and the role of a higher lactam like laurolactam on the moisture absorption characteristics of the copolymers are discussed in our previous publication [23]. 

Table 19. Effect of Polymerization Temperature on Polydiene Chain Structure...

The patents quoted in Table 20 do not give information on the effect of polymerization temperature on reaction rates, molar mass, MMD and cis-1,4-contents. This information is scattered in various scientific reports. The reports which are valuable in this context are summarized in Table 21 for binary Nd catalyst systems and in Table 22 for carboxylate-based systems. 

According to Porri et al. the largest effect of polymerization temperature is on reaction rates [50]. Information on the dependence of reaction rates is contained in most of the reports quoted in Tables 21 and 22. Unfortunately, most of these studies do not provide activation energies. 

We will furthermore present data showing the effect of polymerization temperature on limiting conversion. With polymerizations below the glass transition point of the polymer, the monomer-polymer solution reaches its glass transition point at a conversion <100%. At this point reactions involving small molecules, such as propagation, become diffusion controlled. This causes the rate of polymerization to fall to virtually zero in the normal polymerization time scale, i.e. in practice the reaction rate reaches a limiting conversion <100%. 

Figure 17.15 Effect of polymerization temperature on catalytic activity. Line, calculated by kinetic equation symbols, polymerization results...

Fig. 53. Super active 3rd generation catalyst effect of polymerization temperature on activity and Isotactic Index. Polymerization in hexane at 70 °C, 7 bar, 4 hours...

Effect of Temperature. Table III shows the effect of polymerization temperature on the chain structure of lithium polyisoprene, both in the case of undiluted monomer and in the presence of n-hexane as solvent. Within the ranges shown, there does not appear to be any influence of temperature on the placement of the various isomeric chain unit structures. 

Effect of Polymerization Temperature on Chain Structiire of Lithium Polyisoprene... 

Effect of Polymerization Temperature. The effect of temperature on the polymerization of butadiene is shown in Table V. It can be seen at once that, within the small temperature range... 

Table I. Ethylene Polymerization—Effect of Polymerization Temperature (l)a...

Effect of Polymerization Temperature on the Content of the Vinyl Structure in Polydienes... 

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...

Figure 15.2 Effect of polymerization temperature upon the microstructure of emulsion-polymerized polybutadiene (Hampton [13]) ( ) 1,2 units (A) cw-1,4 units ( ) trans-lA Units...

The effect of polymerization temperature upon the microstmcture of poly-chloroprenes produced by emulsion polymerization is illustrated by the results, reported by I ynard and Mochel [25], shown in Table 15.6. The chloroprene units are present mainly as trans- A structures, irrespective of the polymerization temperature. However, the distribution of the microstructures does depend somewhat upon polymerization temperature. The ratio cw-l,4/tra 5-l,4 units decreases as the polymerization temperature is reduced, but the overall content of 1,4 units increases. The balance comprises 1,2 and 3,4 units in approximately equal proportions, except for polymers produced at very low temperatures, where the 1,2 units predominate over the 3,4 units. A consequence of the overall content of 1,4 units increasing with decreasing polymerization temperature is that the sum of the contents of 1,2 and 3,4 units decreases. As will be seen in Section 15.4.4, although 1,2 units are present in relatively low concentration, their presence is very important for the technology of polychloroprene rubbers. 

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. 

TABLE 2.10 Effect of Polymerization Temperature on Polychloroprene Chain Microstructure ... 

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