Structure Evolution in a Polyurea Segmented Block Copolymer Because of Mechanical Deformation

Abstract

Extensional stress-strain measurements on a polyurea (PU) were carried out at strain rates up to 830 s -1 , in combination with ex post facto small-angle X-ray scattering (SAXS) measurements and temperaturedependent SAXS. The elastomer is of interest because of its application as an impact-resistant coating. The highest strain rates used herein fall within the softening, or transition, zone of the viscoelastic spectrum and are thus relevant to the working hypothesis that the performance of a polyurea impact coating is related to its transition to the glassy state when strained very rapidly. While quasi-static and slow deformation of the PU gives rise to irrecoverable strain and anisotropic SAXS patterns, when stretched at high rates the PU recovers completely and the scattering is isotropic. Thus, the deformation of the hard domains observed at low rates is absent at high strain rates. Linear dynamic mechanical measurements were also carried out, with the obtained segmental relaxation times in good agreement with dielectric relaxation measurements on this material. The PU exhibits the usual breakdown of time-temperature superposition in the transition zone. This thermorheological complexity underlies the fact that published time-temperature shift factors for this material are unrelated to the segmental dynamics, and therefore use of these shift factors to predict the onset of glassy dynamics during impact loading of the PU will be in error.

Impact of the diagnostic label of osteoarthritis on perceptions of disability and willingness to help a parent in African Americans and whites

“…The polyurea (labeled PU1000 in this work) was prepared at Naval Surface Warfare Center. It was based on multifunctional “hard” isocyanate (functionality 2.4) (Isonate 143L from Dow chemical33) and “soft” diamine (Versalink P‐1000 from Air product and Chemicals34)35, 36 and is the same polyurea investigated by Yi et al18 The diamines consist of poly(tetramethylene oxide) (PTMO 1000) repeat units with primary aromatic amine termination. The PTMO component serves as the soft segment for the polyurea, while the terminal aromatic amine and isocyanate components serve as the hard segment.…”

Microstructure and Segmental Dynamics of Polyurea under Uniaxial Deformation

“…1 In this work, we examined the detailed dependence of the latter on the magnitude of the deformation. In the neo-Hookean Figure 11.…”

Multiscale Modeling of the Morphology and Properties of Segmented Silicone-Urea Copolymers

“…Due to the presence of bidentate hydrogen bonding and their higher cohesive energy densities, segmented polyureas display better microphase separation and improved mechanical properties when compared with their polyurethane analogues [16,17]. Based on their backbone compositions, hard and soft segment type and content, segmented copolymers display broad range of properties and find diverse applications [11,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”