CASE STUDY

Exploration and Validationof Polycyanurate
Thermoset Crosslinking
Mechanisms
Molecular dynamics simulations accelerate the development and optimization of nextgeneration aerospace materials

Executive Summary• Accurately predicted key thermophysicalproperties such as glass transition temperature (Tg),density, and coefficient of thermal expansion for thepolycyanurate systems• Built realistic polycyanurate models for the firsttime from its constituent di(cyanate ester) monomer
rather than using prebuilt triazine moieties• Effectively modeled water uptake and location inthermoset matrix by penetrant loading and radial
distribution function analysis• Proposed an alternative water uptake
mechanism for polycyanurate that was notobserved via experimental methods• Enabled rational design of high performance
thermosetting polymers

Challenges

Approach

Thermosetting polymers such as polycyanurates
are important for high temperature applications
in aerospace because of their performance
properties, such as high glass transition
temperatures (Tg) and exceptional flame
resistance. Modeling and simulation efforts
have enabled rapid screening of candidate
materials with targeted properties for highperformance applications without dedicating thesignificant time and resources required for wetchemistry. However, there are challenges forpredicting properties of thermosetting polymers
like polycyanurates:

Scientists from Air Force Research Laboratory(AFRL) and Schrödinger worked together to build
realistic polycyanurate models from its constituent
di(cyanate ester) monomer rather than using
prebuilt triazine moieties, as well as explore thecrosslinking mechanisms. All chemical models
were built and simulations performed using theSchrödinger Materials Science Suite and DesmondMD system:

Validate• The reactions, such as curing/crosslinking, areoften complicated and require multiple factors
to consider• Iterative crosslinking simulation for large
cells containing thousands of reactive groups
was not possible until recent years with theadvances of GPU-accelerated moleculardynamics (MD) simulations

Predict• Generating a realistic model system isparamount in the prediction of properties andstudy of the dynamics, however, there areexceedingly few examples of in situ crosslinkingof di(cyanate esters) for polycyanurate systems
Crosslink

Validate initial model using LECy systems:
The systems were pushed to the highest
conversion attainable using two different
crosslinking algorithms, and densities werecompared to experimental values

Predict other thermophysical properties
of LECy systems after validation: Tg andcoefficient of thermal expansion (CTE) werecompared to experimental values

Crosslink the BADCy and SiMCy systems
using the mechanism that attained
higher conversion

Predict thermophysical properties: Density,volume, CTE, free volume, and water uptake
were compared to experimental values

Predict

LECy: bisphenol E dicyanate ester
BADCy: bisphenol A dicyanate ester
SiMCy: silicon-containing analogue of BADCy

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Results
This work uses MD simulations to form
polycyanurate networks in order to predict
thermophysical properties and probe water
uptake and aggregation behavior at the atomisticlevel. The predictive power of this model isconsidered adequate for further study of otherpolycyanurate systems, whether in formulationor synthesis of novel monomers to evaluate
properties like water uptake or for mechanicalproperty prediction of systems employing theseand other cyanate ester materials.

• Thermophysical properties (Tg, density, CTE) of
the LECy systems crosslinked via the two different
mechanisms aligned well with experimental data
• Multiple thermophysical properties wereprobed for BADCy and SIMCy systems, and thesimulated data showed rank ordering in line withthe experiment• Water overwhelmingly tended to aggregate
together in free volume, rather than closely
associated near specific moieties. However, polar
moieties like triazine rings and phenolic groups
showed an affinity to the water and tended toreside on the periphery of the free volume where
the water is located• New hypothesis was proposed: Increasedhydrophobicity is the driving factor in thedecreased water uptake of SiMCy rather than achange in free volume in the SiMCy monomer

Representative radical distribution functions (RDFs) of water relative to the described moieties in the crosslinked networks. Curves
corresponding to BADCy are in blue, LECy in orange, and SiMCy in gray. Note that the y-axes are not all at the same scale.*3

References
1. Polycyanurates via Molecular Dynamics: In Situ Crosslinking fromDi(Cyanate Ester) Resins and Model Validation through Comparisonto Experiment
Levi M. J. Moore, Neil D. Redeker, Andrea R. Browning, Jeffrey M.
Sanders, and Kamran B. Ghiassi, Macromolecules 2021, 54, 13,6275–6284*The figures were published in the referenced paper.
Copyright ACS Publications.

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