Simulation of the structure and mechanics of crystalline 4,4′-diphenylmethane diisocyanate (MDI) with n-butanediol (BDO) as chain extender

We report molecular simulation, at the atomistic level, of crystalline 4,4′-diphenylmethane diisocyanate (MDI) with n-butanediol (BDO) as chain extender, henceforth denoted as MDI/BDO, which is one of the most important components of thermoplastic polyurethanes. This work studies the structure and properties of crystalline MDI/BDO at equilibrium and under deformation. An atomistic molecular model of the MDI/BDO unit cell was constructed from fractional coordinates available for related model compounds and space group symmetry, and bulk properties of the subsequently equilibrated crystal were estimated by molecular dynamics. Overall stress-strain behavior of the crystal to small strains was simulated. The full stiffness matrix of crystalline MDI/BDO was extracted, allowing for the complete characterization of the linear elastic behavior of the crystal.