PREDICI simulation

It should be noted that Predici simulation of kinetics and of polymer properties is extremely valuable for fitting measured copolymerization data and for extracting the full information contained within the experimental data. Moreover, Predici simulation effectively supports attempts to identify reaction conditions that are best suited to the unambiguous and sensitive determination of kinetic parameters [67]. 

The proposed reaction scheme was employed to successfully model the kinetics of the DTBA-mediated MMA polymerization in the early reaction phase via PREDICI simulations (see Figure 6), resulting in a hydrogen abstraction rate coefficient of fetr = 3.0xl0 L-moE -s and a reinitiation rate of the alkylsulfanyl radical of fejeini = 7.8 L moP The... 

To begin backbiting is accounted for via inclusion of the reaction steps for tertiary radical, formation (la), propagation (Ib) and termination (Ic and Id) into the PREDICI simulation (see Scheme 1). These reactions depend on the rate coefficients for backbiting, febb, tertiary radical propagation, i and tertiary radical termination, which occurs either between two tertiary radicals, o " between a mid-chain and an end-chain radical, where the moiety X represents the continuing chain. Additionally, the model was expanded to account for the reactions for the RAFT... 

The value of the rate coefficient of the missing step reaction in Eq. (3), ltr,int. may come close to or even exceed that of fead, which is the 1 + 2 addition rate coefficient (see Eq. (1)), because within both reactions, at least in the case of acrylate pol3merizations, a highly reactive propagating radical is transformed into a resonance-stabilized one. PREDICI simulations including the reactions presented in Eqs. (2) and (3) have been carried out for dithiobenzoate-mediated methyl... 

In conclusion, the goal of predictive process modelling has not yet been achieved due to the interference of chemical reactions with mass transport. All polycondensation models and process simulators available in the public domain, such as Polymer Plus from AspenTech or Predici from CIT, as well as in-house polycondensation models from engineering companies and producers, cannot be used for design or scale-up successfully without the use of fitting parameters. 

Figure 4.6-8 Simulated (via Predici ) MWDs of polyethylenes produced at 200 °C and 2000 bar at different levels of monomer conversion varying between 2 and 20% in steps of 2% [41].

Ray [34] has discussed several different methodologies (also analytical ones) for calculation of MWDs. A more recent, though very brief discussion on simulation techniques can be found in [35] with particular attention for the commercial package PREDICI. Rees [36] has discussed several aspects of numerical simulations in more detail. 

The evolution of the PDI (=A4 /Mn) more complicated since it would require to take into account all the events of the polymerization. This can be performed by using a numerical simulation (such as PREDICI). Nevertheless, some attempts have been made to obtain some analytical equations in simplified cases. These analytical equations are useful to show the trends. For instance, Muller et studied the particular case of Cm = Cex and neglected radical termination to obtain eqn [20]. 

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