Abstract Morphological variation of thermoplastic polyurethanes (TPUs) with different hard segment contents (HSCs) stretched at 100 °C higher than the Tg of hard domain was monitored by in-situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) techniques. WAXS patterns reveal that the crystalline modification of TPUs with high HSCs transforms from paracrystal (termed as form I) to form III of 4,4′-methylene diphenyl diisocyanate/1,4-butanediol (MDI/BD) segment, and TPUs with low HSCs show the direct transition from amorphous MDI/BD packing to form III packing. The form III crystals are fibrillar hard domains. Chord distribution functions (CDFs) computed from the SAXS patterns were employed to illustrate the domain topology. The streak-like CDF peaks off the meridian indicate the existence of cylindrical microfibrils which are composed of very low inhomogeneities between the destructured hard domains and stretched soft domains along the straining direction. These microfibrils of TPUs with low HSCs present a periodically lateral correlation. Interface distribution function (IDF) and chord length distribution (CLD) were computed from Bonart's longitudinal and transverse projection to quantify the domain stacking and microfibril arrangement respectively. The average size of hard domains increases up to a constant size with the increasing macroscopic strain which may be related to the maximal sequence length of hard segment. The average size of soft domain also reaches up to a constant size at large strain that is smaller than the fully-extended length of soft segment. The variation of domain size is different from deformation at room temperature. The HSC affects the behaviors of morphological evolution significantly.

中文翻译：

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MDI/BD 基聚氨酯中硬链段的结晶在高温下变形及其对 MDI/BD 含量的依赖

摘要 通过原位广角 X 射线散射 (WAXS) 和小角 X 射线散射监测具有不同硬链段含量 (HSC) 的热塑性聚氨酯 (TPU) 在比硬域 Tg 高 100 °C 时拉伸的形貌变化。射线散射 (SAXS) 技术。WAXS 模式表明，高 HSC 的 TPU 的结晶改性从副晶体（称为 I 型）转变为 4,4'-亚甲基二苯基二异氰酸酯/1,4-丁二醇 (MDI/BD) 链段的 III 型，而具有低 HSC 的 TPU HSC 显示了从无定形 MDI/BD 堆积到形成 III 堆积的直接转变。III型晶体是纤维状硬域。使用从 SAXS 模式计算的和弦分布函数 (CDF) 来说明域拓扑。子午线外的条纹状 CDF 峰表明存在圆柱形微纤丝，其由沿应变方向的解构硬域和拉伸软域之间的非常低的不均匀性组成。这些具有低 HSC 的 TPU 微纤维呈现出周期性的横向相关性。从 Bonart 的纵向和横向投影计算界面分布函数 (IDF) 和弦长分布 (CLD)，以分别量化域堆叠和微纤维排列。硬域的平均大小随着宏观应变的增加而增加到恒定大小，这可能与硬段的最大序列长度有关。软域的平均尺寸也在大应变下达到恒定尺寸，小于软段的完全延伸长度。畴尺寸的变化不同于室温下的变形。HSC显着影响形态进化的行为。