Monte Carlo Modelling of Phase Separation in Polymer Blends That Contain Branched Molecules*

Thermoplastic-toughening of thermosetting epoxy resins is becoming increasingly prevalent, particularly for aerospace composites. As the mechanical properties of these materials are highly dependent on morphology, it is extremely important to understand phase separation within blends of branched and linear polymers. Unfortunately, the Flory-Huggins model has significant limitations for systems containing branched polymers. Entropies of branched polymers are often much lower than for linear polymers of the same molecular weight, but the mean field approach of the Flory-Huggins model does not account for this. The impact of polymer conformation on energetic interactions is also ignored. Here, we have developed a simulation approach capable of overcoming these difficulties and calculating free energy for polymers with branched architectures. We have also used Monte Carlo methods to directly simulate concentration fluctuations within industrially relevant blends, and have therefore gained insight into their phase separation characteristics.