Simultaneous small-angle X-ray scattering/wide-angle X-ray diffraction study of the microdomain structure of polyurethane elastomers during mechanical deformation

Abstract

Polyurethane elastomers (PUEs) were prepared with poly(oxytetramethylene) glycol (M n ¼2000), 4,4¢-diphenylmethane diisocyanate, 1,4-butanediol (BD) and 1,1,1-trimethylol propane (TMP) by a prepolymer method. To evaluate the effect of curing temperature and the ratio of curing and crosslinking agents ((BD/TMP)¼(10/0 and 8/2)(wt/wt)) on deformation behavior, four different samples were prepared. In the small-angle X-ray scattering (SAXS) profile for the PUEs prepared at 120 1C, a four-point pattern was observed with the preferred tilt being produced by local torques exerted within the strained soft segments from the initial deformation. At near failure strains, strong meridional scattering appeared and the four-point pattern disappeared. In contrast, the PUEs at 80 1C produced meridional scattering through the deformation. As the microdomain structure of the PUEs prepared at 120 and 80 1C initially possessed cylinder-and sphere-like structures, respectively, the cylinder-like structure might have produced the four-point pattern. Obvious changes in interdomain spacing of PUEs at 120 1C during the deformation process were observed in comparison with the spacing at 80 1C. This was due mainly to the formation of a well-developed, networked, cylinder-like microdomain structure. Strain-induced crystallization of the soft-segment chains evaluated by wide-angle X-ray diffraction results was also consistent with the results from SAXS.

Polyurethanes containing a crystalline polyol and semiflexible urethane segments

“…After stretching materials to λ = 5, the scattering was concentrated along the meridian (ψ = 90°), parallel to the deformation direction. Similar SAXS and WAXS behavior has been observed previously for other polyurethane and poly(urea‐urethane) systems and is attributed to domain orientation and orientation of chains along the deformation direction . Nondeformed samples present isotropic distribution of crystalline lamella while progressive increase in strain promotes orientation of chains parallel to strain and lamella orientation and breakdown .…”

High-extension properties of polyurethane elastomers-effects of variation of the ester isocyanate ratio

“…This is a slow process compared with addition to the hard block to the lateral crystalline block surface and hard blocks are therefore expected to lie perpendicular to the molded surface. Transverse orientation may also be induced by stresses during the cooling of the solid and can be observed as a rotation along the crystalline axis in the direction of stretch . The MDI unit adopts a v‐shaped conformation so that one of the urethane groups can be hydrogen bonded within the stack.…”

“…Transverse orientation may also be induced by stresses during the cooling of the solid and can be observed as a rotation along the crystalline axis in the direction of stretch . The MDI unit adopts a v‐shaped conformation so that one of the urethane groups can be hydrogen bonded within the stack. The second urethane group cannot be hydrogen bonded within the stack but will bond across the chain in an adjacent stack, i.e., the structure will be stabilized by hydrogen bonding in two dimensions .…”

“…This is a slow process compared with addition to the hard block to the lateral crystalline block surface and hard blocks are therefore expected to lie perpendicular to the molded surface. The MDI unit adopts a v‐shaped conformation , so that one of the urethane groups can be hydrogen bonded within the stack. The second urethane group cannot be hydrogen bonded within the stack but will bond across the chain in an adjacent stack, i.e., the structure will be stabilized by hydrogen bonding in two dimensions.…”

“…The interpretation of the constants C 1 and C 2 has been considered by a number of workers . The general conclusion which emerges is that the origins of C 2 are obscure but can be attributed to both the morphology created and the possibility of chai entanglement in the soft matrix.…”