Prediction of molecular weight distribution in chain growth polymerizations

Abstract

This work presents results on the prediction of the molecular weight distributions (MWD) of chain growth polymerization using conventional software and hardware tools. The investigation focuses on two kinds of polymerization processes: free radical batch and continuous polymerization processes with application to low density polyethylene synthesis (LDPE); and coordination polymerization via metallocenes with application to high density polyethylene synthesis (HDPE). For both processes, kinetic models, consisting of sets of differential equations describing the dynamic behavior of all the chemical species in the reaction media, are presented. From these sets is possible to obtain the molecular weight distribution of the polymer^1,2,4

Strategies for the simulation of the polymerization models were developed and results of these simulations are presented. On the free radical polymerization case, the next results are highlighted: i) It was confirmed that the chain transfer to polymer step produces strong asymmetries on the MWD as well as a high polydispersity index; ii) It’s possible to calculate the MWD in the CSTR process through a simulation strategy that permits the decoupling of the live and dead chains populations. On the metallocene polymerization case, it was demonstrated that the coordination standard model represents well the system experimentally studied and it can be employed to directly calculate the molecular weight distribution.

These results confirm the idea that the complete MWD can be directly calculated with conventional hardware and software tools.