Modeling the reaction event history and microstructure of individual macrospecies in postpolymerization modification

Abstract

For postpolymerization modification, a novel kinetic Monte Carlo (kMC) modeling strategy for the description of the reaction event history and the evolution of the microstructure of individual macrospecies with a complex topology is presented. The kMC model allows the kinetic analysis of free radical induced grafting of vinyl monomers onto polyethylene (PE) chains, assuming isothermal conditions and perfect macromixing and accounting for diffusional limitations on the microscale. Not only average characteristics such as the monomer conversion, grafting selectivity and yield, but also the chain length distribution (CLD) of all macromolecular species types, the average “from/to” grafting and cross‐linking density, the number of grafts and cross‐links per individual macromolecule, the chain length of every graft, and the CLD of the grafted chains are calculated. Under typical grafting conditions, depropagation and diffusional limitations cannot be ignored. The functionalization occurs mainly on those macrospecies in the PE‐CLD with a high mass concentration. © 2017 American Institute of Chemical Engineers AIChE J, 2017

The Relevance of Multi‐Injection and Temperature Profiles to Design Multi‐Phase Reactive Processing of Polyolefins

“…The basic principles of the batch k MC model, as previously developed in ref. are given in Section S1, Supporting Information.…”

“…The resulting modified polyolefin can serve both as the polymer matrix and coupling agent with the blend constituents. Depending on the type of functionalizing agent/monomer, the concentration, and the reaction temperature, the graft length can vary between one functional monomer unit and several units . Moreover, according to the type of functionalizing monomer, unwanted homopolymerization can be experienced .…”

“…In order to shed more light on the FRIG synthesis–structure relationship, several models have been proposed . One of the most detailed models is the stochastic one of Hernández‐Ortiz et al in which a monomer‐ and polymer‐rich phase are distinguished on the timescale of reactive processing (second to minute scale), with radical kinetics taking place in both phases, and corrections on the reactivities due to diffusional limitations in the polymer‐rich phase. The latter implies that apparent rate coefficients are considered to account for restricted diffusivities, as encountered under melt conditions.…”

“…So far, application of the model was restricted to case studies in which all reactants were present at the start of the chemical modification, hence, batch polymer modification, with focus on the necessity to account for a multi‐phase system under industrial processing conditions as opposed to a conventional single phase one. Model validation has been successfully performed for a reference monomer considering a stepwise tuning procedure focusing first on the tuning of a limited number of lacking kinetic parameters under large reaction times at which a single phase reaction system can be assumed and then on industrial scale data with multiphase character for the tuning of a limited number of mass transfer parameters…”

“…In the present work, considering kinetic and transport parameters from literature, the developed model is further applied to identify potential of multiple injection of initiator and/or monomer in an ideal tubular reactor configuration. In addition, it is explored if temperature profiles, more precisely different temperatures zones along the axial coordinate, are beneficial.…”