Dedicated to the 60th Birthday of Joao Soares

It gives us great pleasure to see this special edition of Macromolecular Reaction Engineering (MREN) dedicated to our colleague and friend Professor Joao Soares on the occasion of his 60th birthday. Jo's contribution to the field of polymer reaction engineering continues to be outstanding, beginning with the work he did with the great Archie Hamielec in the early 1990s on modelling of polyolefins, and where he first fell in (platonic) love with Stockmayer and his bivariate distributions. After graduating from McMaster University in 1995 he moved first to Waterloo University where he established himself as a world class researcher in the field of catalytic olefin polymerization. In 2013 he moved to the University of Alberta, and significantly expanded his areas of interested to include many different areas, applying his unique approach to PRE problem solving to study water soluble polymers, structure property relationships, and nanocomposites as well. Over the course of these past 25 years Jo has distinguished himself as a world leader in the application of Polymer Reaction Engineering (PRE) tools. Of course, we are looking forward to at least a couple more decades of interesting things from him, but this is a nice opportunity to acknowledge his contributions, and to take at look at how things are changing. Over the years, we have heard many comments and opinions about how mature PRE has become and that it is now a mature field where only incremental work is being done. We think that the papers published in this special issue go a long way to dispelling these points of view. But first we can ask ourselves what polymer reaction engineering is (and is not!). There is of course no one, obvious answer to this question, and different people will have different points of view. However, in a broad sense one can think of polymer reaction engineering as an approach to understanding and quantifying the relationship between reaction conditions, the reactor environment and the properties of the resulting polymer. This involves modelling of polymerisation kinetics, the estimation of rate constants, active centre concentrations, and reaction pathways. It includes understanding residence time distributions and population balances as well as non-ideal thermodynamics and how the composition in the reactor influences the concentration at the polymerization site. And it means going beyond modelling of course; developing experimental tools like hardware and software sensors, experimental methods to look at polymer properties such as chain entanglements or studying the fragmentation of polymerisation catalysts. Lastly, it can even go as far as developing manufacturing strategies and processes, based on mathematical approaches and software tools, for advanced process control methods to control polymer properties. In a previous special issue of MREN we honoured the work of some outstanding engineers who pioneered the study of PRE in North America, Archie Hamielec, Harmon Ray and Charlie Cozewith. In Europe some of the names that spring to mind as pioneers of PRE also include Hans Gerens and Karl Heinz Reichert. All of who were largely responsible for helping to develop and promote this version of PRE. It is somewhat of a cliché, but nonetheless true to say that as time moves on, progress is indeed made on certain issues, and specific problems are solved. For instance, it is probably fair to say that we know how to model the polymerisation of styrene in the melt phase! However, some problems persist – how many of the metal atoms in a Ziegler-Natta catalyst are truly active (and how might this change with time, conditions, etc.)? How can we predict solubilities in complex systems? Will we ever develop a means of predicting the Tromsdorff effect à priori? Furthermore, societal needs are constantly evolving, and we are called upon to think about things like the ecodesign of polymeric materials, (bio)degradation of polymers and their recycling (and rightly so). As we understand better how to make and characterise complex structures, composite materials (either made in the reactor or post-reactor in reactive extrusion for example) are more and more in demand. Moreover, the strategies to integrate these understandings with advanced process control methods will be needed. However, we could argue that it is precisely because the “targets” are moving and not all problems have been solved that polymer reaction engineering remains pertinent. If we consider some of the articles in the current issue dedicated to Jo Soares, this is quite apparent. A very nice article from Alex Penlidis's group demonstrates how to apply a fundamental PRE approach to the development of new materials for a specific application. Other contributions do the same but for polymers that incorporate biomaterials. There are contributions showing new developments in the control of material properties by catalyst modification, and an experimental study on catalyst fragmentation to help us better under this complex phenomenon. An article from POLYMAT discussed the importance of polymer characterisation, and another paper looks at structure-property relationships using a basic PRE approach. We also see some new modelling and new experimental tools for the study of olefin polymerisation, as well as an experimental paper on the impact of non-ideal thermodynamics in ethylene polymerization. All of these are new topics and applications, but ones that rely on the use of PRE tools that we can all identify with. So, much like our friend Jo Soares, the field is changing and evolving, and while it too might look a bit old from the outside, there is still lots of life and exciting developments to come from the field of Polymer Reaction Engineering.

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