A two-phase stochastic model to describe mass transport and kinetics during reactive processing of polyolefins

Free radical induced grafting (FRIG) of polyolefins is described at industrially relevant time scales at which phase segregation occurs, leading to the formation of a monomer-and polyolefin-rich phase. The mass transfer of oligomeric species is accounted for using overall average mass transfer coefficients. Model validation is illustrated for FRIG with a non-homopolymerizable monomer based on experimental data on monomer conversion and functionalization degrees. Comparison with an approximate single-phase model highlights that due to phase segregation the reaction rate and the functionalization degree significantly decrease due to a different role of diffusional limitation on termination, whereas the grafting degree and density are unaffected on an overall monomer conversion basis. This mismatch with the single-phase model is enlarged with a homopolymerizable monomer. The polyolefin-rich phase is there characterized by lower monomer concentrations whose grafting kinetics are strongly affected by depropagation, compensating for influences caused by diffusional limitations on termination. For such monomers, the functionalization selectivity can display even a maximum as a function of the overall monomer conversion.