Activation energy for propagation

Use the data below for the activation energies of some typical addition polymerization reactions at 60° C to calculate an average activation energy for propagation, termination, and initiator decomposition. Each person should calculate one of the three average activation energies. 

The slope of 1/P versus 1/t gives kp and the intercept the sum of the transfer reactions. These are individually resolved by measuring molecular weights as functions of the concentration of each component. The change in slope of 1/Pp versus 1/t with temperature gives the activation energy for propagation, Ep. 

Termination can also occur by the reaction of polymer free radicals with primary initiator radicals (called primary termination) or free-radical scavenging species, especially oxygen. Activation energies for propagation and termination for some typical monomers are listed in Table 2. 

The zero activation energy for radiation initiation, E., leads to some interesting practical consequences. The overall activation for the rate, E = E + 1/2 E - 1/2 E, where E and E are the activation energies for propagation and termination, respectively. Since E. for most catalytic initiation is about 30 and E close to zero, this leads to a value of about 22 kcal per mole compared x ith about 7 kcal per mole for radiation for v/hich E.=0. The practical advantages of this were referred to earlier. 

In the bulk polymerization of styrene by ultraviolet radiation, the initial polymerization rate and degree of polymerization are 1.3x10 mol/L-s and 260, respectively, at 30°C. What will be the corresponding values for polymerization at 80°C The activation energies for propagation and termination of polystyryl radicals are 26 and 8.0 W/mol. What assumption, if any, is made in this calculation ... 

---