Leonard Courapied
Simulation of the homopolymerisation of bismaleimide monomers by tailored reactive Molecular Dynamics

Even if they were initially developed for the electronic industry, bismaleimide resins are used for high performance composite applications, especially when high temperature is the main stress factor for the parts. Derived from the polyimide chemistry, bismaleimides resins are easier to process, more affordable and have limited volatile emissions during their polymerization. Despite these materials being used and studied for many decades to determine their performances, the various chemical reactions implicated in the formation of the polymeric network are not fully described.

The reactions between bismaleimide monomers (crosslinking by homopolymerisation, linear cyclo-polymerisation) and with the Diallyl co-monomers (Alder-ene reaction with allyl comonomer¹, Diels-Alder cyclisation¹) can either be thermally and photoinitiated to form a thermoset polymer. Their respective contribution to the final polymer remains unstudied due to a lack of analysis methods at the solid state to discriminate the created carbon-carbon bonds formed in the cured resin.

Molecular modeling, and more specifically reactive Molecular Dynamics can be a useful tool to help identifying the fundamental structure/property relationships of such system. However, most of the reactive approaches in Molecular Dynamics struggles to describe correctly the reactions of interest in these systems, concerted reaction such as Diels Alder, especially when the reactive groups cannot be simply differentiated using SMARTS notation.

The work presented proposes an alternative approach to cover for the reactive description of a single component bismaleimide resin, made of 4,4’-bismaleimidodiphenylmethane (MDAB), through two types of possible reactions, exhibiting various topological outcomes for the polymeric network and estimating basic properties of extrema simulated systems.

Figure 1. MDAB molecule and its 3D representation.

Two MDAB amorphous systems were considered: a system of 24600 atoms (600 molecules) and a system of 49200 atoms (1200 molecules). The simulation of the reaction and the prediction of the network’s thermomechanical properties are performed using Schrödinger Suite program, using its OPLS4 Force Field.

The comparison of linear MDAB systems with and without cyclic structures shows that the presence of cyclic structures has a minor impact on the mechanical properties when compared to the more significant changes induced by crosslinking. Overall, the simulations highlight the strong impact of crosslinking on improving the mechanical integrity of MDAB polymers, increasing significantly the polymer moduli.

Table 1. The mechanical properties of three different MDAB polymer systems.

Dr.-Ing. Dirk Lehmhus (DE)

Dirk Lehmhus received his mechanical engineering diploma working on galvanic corrosion of magnesium alloys at Volkswagen’s central laboratory in Wolfsburg, Germany, in 1998. He joined Fraunhofer IFAM, the Fraunhofer Institute for Manufacturing Technology and Advanced Materials, the same year, studying metallic foams and structures based on these. He obtained a PhD at Bremen University for studies on optimization of aluminium foam production processes and properties. In May 2009, he changed to the University of Bremen to become managing director of its Scientific Centre ISIS (Integrated Solutions in Sensorial Structure Engineering) dedicated to the development of sensorial materials and sensor-equipped structures, the foundation of which he helped organise, while maintaining his association to Fraunhofer IFAM. Topics covered in this period include integration of sensors in cast as well as additively manufactured components. In January 2018, he returned to Fraunhofer IFAM as senior scientist in the department of casting technology and lightweight construction. Since 2009, he has regularly been involved in topic and symposium coordination at the Euromat and the MS&T conference series, with a special focus on materials for transport applications, additive manufacturing and metal casting. Besides, he helped initiate the International Conference on System-Integrated Intelligence (SysInt), and hosted it in Bremen in 2014 and 2020. Furthermore, he is a member of the Scientific Committee of the International Conference on Engineering Against Failure (ICEAF) conference series. Dirk Lehmhus is member of TMS and DGM, the German materials science association. He is furthermore member of the Editorial Board of the OpenAccess journals “Metals” and “Materials” and has so far published more than 70 scientific papers. His present research interests beyond metal casting and material-integrated intelligent systems include cellular metals and metallic foams, specifically metal matrix syntactic foams, powder metallurgical materials including composites and those produced by additive manufacturing techniques. Within the area of metal casting technology, besides sensor integration, his focus is on low and high pressure die casting (LPDC, HPDC), compound casting, integrated computational materials engineering (ICME) and digitalization aspects. At Fraunhofer IFAM, he is coordinating or participating in several public and industry funded research projects with a focus on casting of light alloys for surface transport applications.

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