Propagation activation energy

A look into values of Ch from previously presented experimental data for the FRRPP of styrene in ether was made. If the polymerization rate is solely based on propagation reaction between the monomer and the live polymer radicals, then from Table 2.4.3, the effective activation energy for k in Eq. (2.2.3) is the same as the propagation activation energy of 7,051 cal/mol K. With a reactor operating temperature of 80°C, this results in a dimensionless activation energy of y = 10. Table 2.5.1 shows that this value of y provides results within the cutoff of Ch < -1,000 for FRRPP to occur. 

Table 6.4 Rate Constants at 60 C and Activation Energies for Some Propagation Reactions...

In general, the activation energies for both cationic and anionic polymerization are small. For this reason, low-temperature conditions are normally used to reduce side reactions. Low temperatures also minimize chain transfer reactions. These reactions produce low-molecular weight polymers by disproportionation of the propagating polymer ... 

The number of active centers determined by the quenching technique was dependent on the polymerization temperature (98) that was the reason for the difference between the overall activation energy and the activation energy of the propagation step. 

The propagation rate constant did not depend on the monomer concentration which corresponds to the first-order propagation step. The activation energy of the propagation calculated according to the variation of Kp with temperature was found to be 6.5 0.5 kcal/mole. 

Frequency factors for addition of small radicals to monomers are higher by more than an order of magnitude than those for propagation (Table 4.12). Activation energies are typically lower. However, trends in the data are very similar suggesting that the same factors are important in determining the relative reactivities for both small radicals and propagating species. The same appears to be true with respect to reactivities in copolymerization (Section 73.1.2)/88... 

Even though the absolute rate constant for reactions between propagating species may be determined largely by diffusion, this does not mean that there is no specificity in the termination process or that the activation energies for combination and disproportionation are zero or the same. It simply means that this chemistry is not involved in the rate-determining step of the termination process. 

Bond energies. The net reaction CD + RH = RC1 + HC1 proceeds by a chain mechanism in which the propagators are Cl and R (but not H ), and chain-breaking occurs by dimerization of Cl. Write a scheme consistent with this and derive its rate law. Show how one can use E and AH for the bond dissociation of CP to calculate an activation energy for an elementary reaction. 

The activation energy of the propagation reaction (Ep) and that of association equilibriim reaction (Eeq) are reported to be 6.13 Kcal/gmole and 38.6 Kcal/gmole respectively ( ). A non-linear search of the data (Equation 14) will define the constants a b c, and d. Data at 16.6 C and 21 C were incorporated with a least square objective function using Luus and Jaakola s (18) method. The analysis resulted in the following relationships ... 

Activation energy of propagation reaction in the Arrhenius equation... 

E 3,p,E = activation energy for dissociation, propagation and termination respectively (KJ/mol)... 

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