Cross-Linking Methodology for Fully Atomistic Models of Hydroxyl-Terminated Polybutadiene and Determination of Mechanical Properties

Abstract

A computational method for preserving the equilibrated structure of a fully atomistic model of a prepolymer melt while introducing cross-links is introduced. An atomistic model of hydroxyl-terminated polybutadiene (HTPB) is cured using isophorone diisocyanate (IPDI) to form an HTPB-IPDI elastomer. After cross-linking, the elastomer is quenched to several different temperatures and subsequently stressed via both compressive and tensile deformations to assess mechanical properties as a function of temperature. This study establishes the framework for investigating the degradation and embrittlement of HTPB-IPDI binders by molecular simulation.

A Molecular Simulation Approach to Bond Reorganization in Epoxy Resins: From Curing to Deformation and Fracture

“…Indeed, with increasing degree of cross-linking, the initially mobile precursors are locked into a permanent network and the system evolves to a stiff epoxy resin. As a consequence, only the onset of thermoset curing is accessible to direct molecular dynamics (MD) or Monte Carlo (MC) simulation, and efficient protocols for assigning suitable binding partners are needed at later stages of network formation. ,,,, Despite ongoing progress, so far molecular simulation models still fall short of achieving the almost 100% degree of cross-linking that is reached in epoxy resins used in industrial applications . The current benchmark of 93% cross-linking was obtained from a combined quantum mechanical/molecular mechanics approach that used smooth topology transfers , to facilitate network relaxation in the course of linking candidate pairs of reactants .…”

“…This ignores possible bond dissociation and reorganization at later stages of network formation. However, it is intuitive to expect that local corrections of the forming polymer network may help to avoid internal stress . As a consequence, molecular simulation protocols should ideally describe the reactivity of all epoxy moieties in a simultaneous manner.…”

“…However, it is intuitive to expect that local corrections of the forming polymer network may help to avoid internal stress. 21 As a consequence, molecular simulation protocols should ideally describe the reactivity of all epoxy moieties in a simultaneous manner. Unfortunately, this diminishes the performance of quantum mechanical/molecular mechanics approaches drastically, as practically the entire system must be described as the reactive species.…”

Quantum Chemical Modeling of Propellant Degradation

“…However, Tow and Maginn have devised a strategy that allows the insertion of cross-links between neighboring −OH groups while avoiding the shortcomings of other methodologies. 1,2 An appealing approach for the prediction of probable degradation and cross-linking patterns that may occur in an aging propellant system like HTPB is the use of accurate ab initio quantum chemistry (QC) methods. It does not appear that QC methods have previously been applied to this problem.…”

Hexogen Coating Kinetics with Polyurethane-Based Hydroxyl-Terminated Polybutadiene (HTPB) Using Infrared Spectroscopy

“…Moreover, polyurethane formation in bulk and solution conditions has also been reported from the analysis of characteristic functional group changes based on infrared absorption data [ 22 , 23 ], viscosity change (rheology) [ 11 , 12 , 13 , 14 , 15 , 16 ], magnetic resonance/NMR [ 24 , 25 ], and heat flux [ 18 , 26 ]. Further, polymerization of polyurethane formation from HTPB with IPDI has also been conducted in both bulk and solution conditions [ 18 , 20 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. The polymerization consists of several steps involving two hydroxyl groups in HTPB and two isocyanate groups.…”