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

Polyurethane elastomers (PUEs) were prepared with poly(oxytetramethylene) glycol (M_n=2000), 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)=(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 °C, 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 °C produced meridional scattering through the deformation. As the microdomain structure of the PUEs prepared at 120 and 80 °C 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 °C during the deformation process were observed in comparison with the spacing at 80 °C. 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.