The deformation behavior of polythiourethane
(PTU) elastomers was
investigated using in situ small-angle X-ray scattering (SAXS), wide-angle
X-ray diffraction (WAXD), and X-ray absorption fine structure (XAFS)
methods. Two PTUs were prepared from poly(oxytetramethylene) glycol,
1,4-bis(isocyanatomethyl) cyclohexane, and 1,4-butanedithiol (PTU-B)
or 1,5-pentanedithiol (PTU-P). The effect of methylene length of the
chain extender on molecular aggregation structure of PTU during the
elongation process was evaluated. SAXS measurement revealed that the
spacing of hard segment domains of PTUs increased and decreased in
the directions parallel and perpendicular to the elongation direction
and showed a constant value of strain above 2. The strain calculated
from the spacing of the hard segment domains for PTU-B was larger
than that for PTU-P, suggesting that well-developed hard segment domains
were formed for PTU-B. WAXD measurement showed that strain-induced
crystallization of the soft segment occurred at around the strain
of 2. XAFS measurement showed that at the strain of 2 or 3, atoms
in the vicinity of sulfur became more ordered, which is confirmed
by the decrement of the extended XAFS Debye–Waller factor.
It seems reasonable from these SAXS, WAXD, and XAFS results that the
hard segment domains orientation occurred for both PTUs during the
deformation process, followed by strain-induced crystallization of
the soft segment. In addition, PTU-B exhibits more ordered hard segment
domains that maintain their aggregation structure upon uniaxial deformation
in comparison with PTU-P.