POSTPOL is a basic research project concerned with the application of static mixers for post-reactor modification of polymers. Such mixers can provide cost effective solutions (compared to, for example, extruders) to the problem of mixing a small quantity of low viscosity reactant into a high viscosity molten polymer stream. The POSTPOL approach has been to develop and validate an integrated set of models to enable the performance of a static mixer to be assessed. Within the model set are included kinetics models, micro and macro mixing models. Experimental data has been collected to validate the models. This includes Laser Induced Fluorescence (LIF) to validate the macromixing (CFD) models and test work on two industrially relevant reaction schemes. A novel test reaction scheme has been developed, which can be used with high viscosities and in rapid mixers. Experimental data has been collected on the effect of viscoelasticity on pressure drop and residence time distribution. An integrated model has been produced which directly integrates the kinetics models with a micromixing model (Ottino). A set of design guidelines has been produced which identifies how all the component models (and experimental data) can be brought together to assist in the design of static mixer reactors for post-polymerisation processing.