Chain-Transfer to Polymer and P-Scission

An alternative description of the transfer to polymer process has been suggested by Goto et al. [35]. They also assume the transfer to polymer rate, eq (4.6-9), to be proportional to the chain length of the reacting polymer. By introducing the P-scission step, eq (4.6-10), for branched intermediate macroradicals Rq, the steep rise in toward high conversion is avoided. 

In contrast to the kinetic picture of independent transfer to polymer and P-scission reactions underlying eqs (4.6-9) and (4.6-10), Lorenzini et al. [34] assume that the transfer to polymer process takes place as a reaction sequence 

Both the Goto et al. [35] and the Lorenzini et al. [34] models are well suited to fit the experimental long-chain branching index /lcb (number of branches per 1000 chain carbon atoms), the measured Afw, and also the full MWD. In LDPE modeling, the scheme of Goto et al., eqs (4.6-9) and (4.6-10), is frequently favored because of a reduced stiffness of the differential equations associated with this approach. If the type and the concentration of branched macroradicals need to be specified, as is desirable in copolymerization modeling, the scheme of Lorenzini et al. [34] appears to be more suitable. 

As mentioned above, the Goto et al. [35] scheme is frequently used for modeling ethene homopolymerization, and the associated ktr.p and kp coefficients 

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