Description and Prediction of Polymer Phase Behavior with Lattice Cluster Theory: An Homage to One of the Great Experimentalists

When chemical engineers are faced with mixtures containing polymers, many difficulties arise, which are not present for other systems. For example, polymers are often poly-disperse with respect to molar mass, chemical composition and branching. Concerning the latter, they can have many different architectures starting from linear over short-chain branched to hyper-branched polymers. Aside from being hard to even characterize, these difficulties make modeling and even more prediction of phase behavior a very challenging task at least. The phase behavior of polymers is not only hard to model, but also experimentally very challenging to determine and it needs a tremendous effort to arrive at reliable experimental data, which is again crucial for developing and testing thermodynamic models of polymers. One of the biggest names in the area of experimental investigation of polymer phase equilibria is Theo de Loos. We try to highlight here on the example of our works on lattice cluster theory, how large the impact was that he has made on our research and our quest for understanding the polymer phase behavior. For this purpose, we go through the different equilibria, i.e. solid-liquid, liquid-liquid, vapor-liquid, solid-liquid-liquid, and vapor-liquid-liquid we have described or predicted over the past years using lattice cluster theory and discuss the challenges associated with polymer phase equilibria, the applicability and limits of lattice cluster theory as well as possible extensions of the theory and combinations thereof with other theories. Not much to our surprise, in almost all of our publications on these topics we have used at least some experimental data of Theo de Loos, showing just how important reliable experimental data is to the application of lattice cluster theory as an engineering tool and to its further development.