The Application of Transmission Electron Microscopy on the Study of Polymer Crystal Structure and Growth Mechanism

摘要

Fruitful ways of molecular packing in the ordered phases formed by long-chain molecules are directly linked to various applications that can be possibly developed from soft materials. However, due to the complicated natures of long-chain molecules, it is frequently met that many mechanisms able to influence and govern molecular assembly and crystallization behavior still wait to be further investigated and learned. The studies on the packing of polymer provide the possibility to reveal the knowledge at molecular level, which might be elusive for other techniques, about how these long-chain molecules continuously join into the crystalline phase or other types of ordered phases. Reported in this article, single crystal diffraction pattern of Form II crystalline modification of poly-4-methyl-pentene-l (P4MP) obtained by TEM surprisingly helps to decipher an unusual monoclinic structure, which has lower symmetry than what have been previously learned based on X-ray powder and NMR spectrums. It is suggested that this lower symmetry of Form II results from conformational restrictions set by chain folding on the stem chirality and clinicity of helical polyolefins, and this structural analysis is well consistent with the single crystal growth habit (preferred ac growth planes). And the adjacent-reentry mechanism should be adopted in the crystal growth.