**Preface to "Modeling and Simulation of Polymerization Processes"**

Polymer reaction engineering (PRE) is the branch of engineering that deals with the technology of large-scale polymer production and the manufacture of polymer products through polymerization processes. PRE is a broad and multidisciplinary area, relatively young and developing fast, combining polymer science, chemistry, and technology with the principles of process engineering. The practical history of PRE started and evolved during the first half of the twentieth century. The 1930s were rich with theoretical findings in polymer science and engineering and with the commercial production of several new polymers. These investigations would transform our understanding of polymer manufacture and culminate in the development of several continuous polymerization processes and the establishment of PRE as a new area of research in the 1940s. The period from 1950 to 1990 saw the continued growth and evolution of process technologies, largely stimulated by the combination of PRE principles with the fundamental understanding of polymerization kinetics developed in earlier years. These principles include the development of mathematical models for polymerization processes and their solution using mathematical packages or specialized chemical engineering or polymerization software. The modeling and simulation of polymerization processes (MSPP) has been fundamental in the development of polymerization technologies since the early stages of PRE to date.

The importance of MSPP has already been recognized by MDPI Processes. A few related issues have been published in the last few years: "Computational Methods for Polymers", Masoud Soroush, August 2019; "Modeling, Simulation and Control of Chemical Processes", Jose Carlos Pinto, ´ 2019; "Renewable Polymers: Processing and Chemical Modifications", Marc A. Dube and Tizazu ´ Mekonnen, March 2019; "Process Modelling and Simulation: Cesar de Prada, Costas Pantelides and Jose Luis Pitarch, February 2019; and "Polymer Modeling, Control and Monitoring", Masoud Soroush, February 2016.

The previous issues of *Processes* on related PRE topics have focused on recent specialized topics. This Special Issue on "Modeling and Simulation of Polymerization Processes"aimed to address both new findings on basic topics as well as the modeling of emerging aspects of product design and polymerization processes. It provides a nice view of the state of the art with regard to the modeling and simulation of polymerization processes. The use of well-established methods (e.g., the method of moments) and relatively more recent modeling approaches (e.g., Monte Carlo stochastic modeling) to describe the polymerization processes of long-standing interest in industry (e.g., rubber emulsion polymerization) to polymerization systems of more modern interest (e.g., RDRP and plastic pyrolysis processes) are comprehensively covered in this Special Issue.

We are indebted to Prof. Alexander Penlidis, from the University of Waterloo, in Canada, who suggested our names for this Special Issue, and for his continuous help and guidance in key aspects of our academic paths.
