Predicting the flow of polymers under melt processing: from reaction kinetics to viscoelasticity

When polymer molecules are functionalized by reactive extrusion, the presence of a radical-initiated complex reaction network makes the prediction of molecular topology based viscoelastic properties difficult. Using both computational chemistry and model compound studies, a mechanistic model for radical-mediated grafting of vinyl silane monomers by melt phase processing was developed. On the basis of the intrinsic kinetic dataset discerned from a hybrid quantum calculation procedure and NMR+GC/MS spectroscopy of model compound studies, quantitative relationships between the product properties and the reaction conditions are also revealed. As a demonstration on the predictive power of the model, a factorial design of experiment is performed with a number of industrial grade polyolefin samples being made from various combinations of reaction conditions and characterized by FTIR and linear rheology. By combining our recently developed viscoelastic model with the access to molecular architecture inferred from high temperature GPC, the predictions on both the yields of the graft content and the evolution of rheological moduli with respect to different processing conditions are found to be quantitively consistent with those of experimental measurements.