Frontal Polymerization of Dicyclopentadiene: A Numerical Study Elyas Goli, †,∥ Ian D. Robertson, ‡,∥ Philippe H. Geubelle,* ,§,∥ and Jeffrey S. Moore ‡,∥ † Department of Civil and Environmental Engineering, University of Illinois, Urbana, Illinois 61801, United States ‡ Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States § Department of Aerospace Engineering, University of Illinois, Urbana, Illinois 61801, United States ∥ Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801, United States ABSTRACT: As frontal polymerization is being considered as a faster and more energy efficient manufacturing technique for polymer−matrix fiber-reinforced composites, we perform a finite-element-based numerical study of the initiation and propagation of a polymerization front in dicyclopentadiene (DCPD). The transient thermochemical simulations are complemented by an analytical study of the steady-state propagation of the polymerization front, allowing to draw a direct link between the cure kinetics model and the key characteristics of the front, i.e., front velocity and characteristic length scales. The second part of this study focuses on the prediction of the temperature spike associated with the merger of two polymerization fronts. The thermal peak, which might be detrimental to the properties of the polymerized material, is due to the inability of the heat associated with the highly exothermic reaction to be dissipated when the two fronts merge. The analysis investigates how the amplitude of the thermal spike is affected by the degree of cure at the time of the front merger. ■ INTRODUCTION Current manufacturing techniques for fiber-reinforced poly- mer−matrix composites typically rely on the bulk polymer- ization of the matrix and often involve expensive processes where the manufactured part is exposed to long and complex temperature and pressure cycles. 1 The manufacturing costs are compounded by the associated need for large infrastructures such as autoclaves and heated molds. 2 In this project, frontal polymerization (FP) is proposed as an alternative to reduce the capital investment and make the fabrication process of fiber- reinforced composites faster and more energy efficient. FP is a class of self-propagating reactions driven by exothermic polymerization. In this reaction, an advancing front is formed by a local thermal stimulus applied to a solution of monomer and initiator. The heat generated by the exothermic reaction advances the propagating front, resulting in a self-sustained process. Various polymer chemistries can perform FP. The main requirement is that the polymerization reaction needs to be highly exothermic. Additionally, the rate of polymerization needs to be high enough to release thermal energy faster than it is lost to the environment. The FP chemistries most explored thus far include anionic and cationic polymerization of epoxy, 3−7 free radical polymerization of olefins, 8−11 addition polymerization of polyurethanes, 12−14 and ring-opening meta- thesis polymerization of dicyclopentadiene (DCPD). 15−18 Frontal ring-opening metathesis polymerization (FROMP) of DCPD is particularly interesting because it exhibits high velocity fronts that produce high quality DCPD polymer, making it potentially useful for rapid manufacturing of large structural components. In this preliminary study, we investigate the initiation and propagation of a polymerization front in the matrix phase only, building on related analytical and numerical studies of FP, which have focused on analytical solutions and small scales. Solovyov et al. 19 developed a mathematical model for the frontal propagation of a highly exothermic polymerization reaction in a methacrylic acid and n-butyl acrylate with peroxide initiators. Goldfeder et al. 9 investigated analytically the degree of cure and frontal velocity in an adiabatic acrylate FP system. They also developed a mathematical model of propagating free- radical polymerization fronts using complex initiation. 20 Other Received: December 14, 2017 Revised: March 28, 2018 Article pubs.acs.org/JPCB Cite This: J. Phys. Chem. B XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.jpcb.7b12316 J. Phys. Chem. B XXXX, XXX, XXX−XXX