Microstructure and Segmental Dynamics of Polyurea under Uniaxial Deformation

Abstract

Polyureas, formed by the rapid reaction between isocyanates and diamines, are attractive for various applications due to their outstanding mechanical properties, which can be tuned by varying component chemistry, molecular weight, and stoichiometry. Polyureas synthesized from a modified methylene diphenyl diisocyanate (Isonate 143 L) and polytetramethylene oxide-di-p-aminobenzoate (Versalink P1000) are widely utilized and investigated for energy absorbing applications such as impact mitigation and ballistic protection. In order to develop a more complete understanding of their mechanical response, we explore the effect of uniaxial strain on the phase separated microstructure and molecular dynamics. We utilize wide-and small-angle X-ray scattering to investigate amorphous segment and hard domain orientation, and broadband dielectric spectroscopy for interrogation of the dynamics. Uniaxial deformation was found to significantly perturb the phase-separated microstructure and chain orientation and result in a considerable slowing down and broadening of the polyurea soft phase segmental relaxation.

Understanding the role of isocyanate dilution toward spraying of polyurea

“…Polyurea is an elastomeric polymer formed by the step growth polymerization of a difunctional isocyanate (NCO) with amines . This class of elastomer has gained a lot of interest by both academia and industry in the last few years, in view of their ability to exhibit a range of mechanical properties, which in turn is an indirect manifestation of its composite microstructure . Polyurea is finding interesting applications in specialized fields, especially as linings in personnel‐protective gear, retrofits for unreinforced structures, and as ballistic‐penetration resistant metallic armor …”

“…The inherent microstructure of polyurea comprise of two distinct types of domains: “hard” realms formed by hydrogen bonded polar urea linkages (NHCONH) and “soft” domains, consisting of long aliphatic polyether chains . Bidentate H‐bonding between the urea linkages result in the formation of nanometer‐sized ribbon‐shaped segments, which act as physical crosslinks between the chains …”

Phase Separated Microstructure and Structure–Property Relationships of High Strain Rate Elastomeric Polyureas

“…The dynamics of the strained polyureas were investigated using DRS [19,22]. The soft phase segmental relaxation slowed down systematically with increasing strain -the dynamic glass transition temperature increased by approximately 30°C at the highest strains used in this study (400%).…”

“…The influence of uniaxial deformation on morphology and dynamics of the baseline bulk polymerized P1000 polyurea was conducted in collaboration with Daniel Fragiadakis and C. Michael Roland (NRL DC) [19]. Although the mechanical strains imposed in this study were higher than those typically encountered for TBI, the behavior of these materials under strain and after relaxation reveal valuable information about the deformation mechanics.…”

Microphase separation and mechanical properties of the polyurethanes based on the high soft segment poly(bis‐azidomethyl oxetane)/tetrahydrofuran binder

“…p(BAMO/THF) binder, as a kind of energetic polyurethane, its performances are strongly dependent on their phase separated morphologies and the degree of the unlike segments segregation, like other polyurethanes . However, the content of the soft segment in binder, containing the azide group, is generally higher to improve the energy performance of propellant, the hard segment hardly forms hard segment domain individually, which makes the structure and properties of this polyurethane are different from the general polyurethanes .…”