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Structure of Negative Spherulites of Even–Even Polyamides. Introducing a Complex Multicomponent Spherulite Architecture
Macromolecules ( IF 5.5 ) Pub Date : 2018-07-05 00:00:00 , DOI: 10.1021/acs.macromol.8b00915
B. Lotz 1 , S. Z. D. Cheng 2 , C. Y. Li 3
Affiliation  

Even–even polyamides are known to grow as positive spherulites, which implies that the radial, fastest growth direction is parallel to the a-axis and hydrogen bond direction. However, after annealing/self-seeding close to Tm, crystallization in a limited Tc window (down to ≈20 °C below Tm) yields profuse negative spherulites and, frequently stemming from the latter, less frequent and ill-defined entities named “spherulitic aggregates”. The detailed structure and origin of these two entities, and especially of the negative spherulites, are still not clearly established although they were first observed some 70 years ago. The recent recognition that polymer spherulites (specifically, spherulites of PVDF in its γ phase) are made of scrolled, radiating lamellae and the observation and analysis of solution grown, scrolled nylon-66 single crystals provide useful guidelines for a renewed analysis of this structural puzzle. The present analysis relies heavily on the approach and on the detailed diffraction data obtained by Lovinger in the late 1970s. It strongly supports the contention that negative spherulites of even–even polyamides are made of scrolled lamellae. The hydrogen bonds are oblique to the spherulite radius. Twinning parallel to the hydrogen-bonded sheets generates two different orientations of the unit cell that helically wind around the scroll axis. These two cell orientations plus a contribution of aggregate-like lamellae that grow inside the radial scrolls account for the apparent lack of orientation of the unit cell in these negative spherulites. This model explains also the birefringence variation of negative spherulites with Tc and their melting point identical to that of aggregates. Negative even–even PA spherulites thus illustrate an original spherulite architecture in which one population of lamellae generates a scaffold within which a second population develops in a confined but oriented frame. It appears to be applicable, perhaps with variants, to the spherulite structure of other types of polyamides.

中文翻译:

甚至偶数聚酰胺的负球晶的结构。引入复杂的多组分球晶体系结构

甚至偶数聚酰胺都可以以正球晶的形式生长,这意味着径向最快的生长方向平行于a轴和氢键方向。但是,在接近T m的退火/自种化之后,在有限的T c窗口(低于T m约≈20°C)内结晶)会产生大量的负球晶,并且经常是由后者产生的,频率较低且定义不清的实体(称为“球晶聚集体”)。尽管这两个实体,尤其是负球晶的详细结构和起源,尽管大约70年前首次观察到,但仍不清楚。最近的认识是,聚合物球晶(特别是γ相中的PVDF球晶)是由涡旋的辐射薄片制成的,对溶液生长的涡旋尼龙66单晶的观察和分析为重新分析这种结构难题提供了有用的指导。目前的分析在很大程度上依赖于该方法以及Lovinger在1970年代后期获得的详细衍射数据。它强烈支持这样的论点,即偶数甚至是聚酰胺的负球晶都是由卷状薄片制成的。氢键倾斜于球晶半径。平行于氢键合板的孪晶产生了晶胞的两个不同方向,它们围绕涡旋轴螺旋地缠绕。这两个晶胞取向加上在径向涡旋内部生长的聚集体状薄片的贡献,解释了在这些负球晶中晶胞明显缺乏取向的现象。该模型还解释了负球晶的双折射变化与 这两个晶胞取向加上在径向涡旋内部生长的聚集体状薄片的贡献,解释了在这些负球晶中晶胞明显缺乏取向的现象。该模型还解释了负球晶的双折射变化与 这两个晶胞取向加上在径向涡旋内部生长的聚集体状薄片的贡献,解释了在这些负球晶中晶胞明显缺乏取向的现象。该模型还解释了负球晶的双折射变化与T c和它们的熔点与聚集体的熔点相同。因此,负偶数甚至是PA球晶都说明了原始的球晶结构,其中一群晶状体产生了一个支架,第二个晶状体在一个狭窄但定向的框架内生长。它似乎适用于其他类型的聚酰胺的球晶结构(可能有其变体)。
更新日期:2018-07-05
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