Curly morphology of β'-crystals of poly(butylene-2,6-naphthalate)

Crystallization of PBN at high temperature leads to growth of highly non-isometric beta'-crystals, with their long and short dimensions being several mu m and 10-20 nm, respectively. In the needle-like or lamellar crystals, molecular segments/stems are oriented parallel to their short dimension, as concluded from polarized-light optical microscopy (POM). In the early stage, the growth of beta'-crystals is straight while in the later stages, when exceeding a critical length, distinct bending and circular growth occurs. These features cause an unusual appearance of the semicrystalline structure when viewed by POM. The spherulitic growth is uneven in the various directions of space, the spherulite surface appears frayed due to missing space-filling and reduced branching, and the finally curly crystal morphology yields a spotty decoration. The analysis of the morphology of beta'-crystals of PBN is expected yielding an improved understanding of structure-property-relations, as these crystals may form at specific melt-processing conditions.