The Spherulitic Crystallization of Isotactic Polypropylene From Solution: On the Evolution of Monoclinic Spherulites From Dendritic Chain-Folded Crystal Precursors.
The Spherulitic Crystallization of Isotactic Polypropylene From Solution: On the Evolution of Monoclinic Spherulites From Dendritic Chain-Folded Crystal Precursors.
复制标题
DOI：
10.6028/jres.070a.006
复制
发表时间：
1966
期刊：
影响因子：
--
通讯作者：
F. Khoury
中科院分区：
文献类型：
--
作者：
F. Khoury
聚丙烯可以从聚合物在不同溶剂中的中等浓度溶液中以单斜（Natta）球晶的形式结晶。一项研究涉及光学和电子显微镜，这导致了不寻常的结构和形态的树枝状前体晶体的表征，从这种球晶的演变，以及这些前体逐步退化成球晶的方式。上述聚丙烯枝晶的整体形状近似于矩形平行六面体（参考轴x、y、z，其中x/y ≥ 1.1且y> 2 z）的形状。这些枝晶由单层链折叠的层状分支的致密但不紧凑的网络组成，所述层状分支相对于枝晶的矩形x，y横截面对角地穿过枝晶，各个层状分支的折叠表面（即，每个分支中的组成分子在其之间来回折叠的那些面）垂直于x，y横截面。电子衍射数据表明，b-结晶轴的取向是唯一的整个交叉线阵列的层状分支，是平行于z，后者的轴对应的方向最慢的生长的枝晶作为一个整体，以及其组成的分支。根据上述特征，结合电子衍射数据，并考虑两种不同的但似乎合理的孪晶模型，还推断出片层枝的折叠面为（001），交叉枝中c晶轴之间的夹角约为80°。这种不寻常的模式的孪生，其中包括一个80°的变化，在后代分支的链轴的方向，在父分支，可能的起源进行了简要介绍。单斜聚丙烯球晶从异常孪晶的树枝状晶体前体的演变过程与球晶在其他聚合物的演变形成对比;此外，在这项研究中提出的意见的相关性，以了解以前报道的非典型的精细结构的起源单斜球晶的聚丙烯从熔体结晶，进行了讨论。
Polypropylene can be crystallized in the form of monoclinic (Natta) spherulites from moderately concentrated solutions of the polymer in different solvents. A study is presented involving both optical and electron microscopy which has led to the characterization of the unusual structure and morphology of the dendritic precursor crystals from which such spherulites evolve, as well as the manner in which these precursors degenerate progressively into spherulites. The overall shape of the above mentioned polypropylene dendrites approximates that of a rectangular parallelepiped (reference axes x, y, z, where x/y ≈ 1.1 and y> 2z). These dendrites consist of a dense but not compact network of monolayer chain-folded lamellar branches which traverse the dendrite diagonally with respect to its rectangular x, y cross section, the fold surfaces of the individual lamellar branches (i.e., those faces between which the constituent molecules in each branch fold back and forth) being normal to the x, y cross section. Electron diffraction data indicate that the orientation of the b-crystallographic axis is unique throughout the cross-hatched array of lamellar branches and is parallel to z, the latter axis corresponding to the direction of slowest growth of the dendrite as a whole as well as its constituent branches. It has also been deduced on the basis of the above features coupled with electron diffraction data and consideration of two different but plausible model twinned dendrites that the fold surfaces of the lamellar branches are (001) and that the angle between the c-crystallographic axis in intercrossing branches is circa 80°. The possible origin of this unusual mode of twinning, which involves an 80° change in the orientation of the chain axes in offspring branches from that in parent branches, is briefly presented. The process of evolution of monoclinic polypropylene spherulites from the unusually twinned dendritic crystal precursors is contrasted with the evolution of spherulites in other polymers; furthermore, the relevance of the observations presented in this study to an understanding of the origin of the previously reported atypical fine structures exhibited by monoclinic spherulites of polypropylene crystallized from the melt, is discussed.