In a previous neutron reflectivity(NR) measurement (RB620370) on CRISP, we showed that the insoluble interlayer formed between the charge injection layer and a semiconducting polymer layer during annealing is an alloy of the the semiconducting polymer and the main component of the charge injection layer, polystyrene-sulfonate(PSS) polymers. We wish to explore further into this area, investigating whether there will be the same interfacial changes occur between simpler polymers such as PMMA or poly(styrene) and PSS? Preliminary lab measurements indicate that this is the case. We wish to use the unique combination of spatial resolution and isotopic sensitivity offered by NR to study PMMA-PS bilayers before, during and after annealing to obtain a fuller understanding of this process.