Crystallization of isotactic polystyrene from solution

Abstract

Difficulties previously encountered in the growth of chain‐folded single crystals of isotactic polystyrene suitable for study by electron microscopy and electron diffraction have been overcome using very poor solvents (including atactic polystyrene of low molecular weight). The hexagonal lamellar crystals produced are relatively stable under electron bombardment and, as a consequence, dark‐field moiré patterns produced by double diffraction from overlapping layers are easy to study. These patterns show no evidence of differences in lattice spacing between fold and nonfold planes such as have been reported in single crystals of several other polymers. Such differences were attributed to congestion at fold surfaces and their absence in polystyrene, for which the surface energy of fold surfaces is small, supports this interpretation. A comparison of crystallization kinetics of polystyrene crystals grown from good and from poor solvents reveals differences in growth rates of three or more orders of magnitude at comparable supercoolings. This disparity cannot be accounted for by acceptable adjustments of thermodynamic parameters in current theories of crystallization with chain folding. The role of molecular conformation in solution appears to exert an unexpectedly large influence on crystallization rate.

Structure of Polymer Single Crystals

“…Isotactic polystyrene single crystals (Keith et al, 1970) could be extracted from the surrounding melt after quenching and dissolution of the, by then, vitrified melt. Similarly, random block copolymers of poly(butyleneterephthalate) and poly(tetramethylene ether glycol) can form single crystals when grown from the melt in spite of their molecular complexity; fractionation by sequence length of the crystallizable poly(butyleneterephthalate) was demonstrated (Briber and Thomas, 1985).…”

“…Investigation of lamellar crystals embedded in a matrix of the same material constitutes of course an experimental challenge. The problem can be alleviated in part by resorting to thin film growth (which may introduce extraneous influence in view of constrained geometry and diffusion problems) or the use of media which mimic the molten polymer, e.g., atactic polystyrene as a noncrystallizing molten medium for isotactic polystyrene (Keith et al, 1970) or n-paraffins as a substitute for molten polyethylene (Keith, 1964).…”

Supermolecular structure of poly(ethylene oxide) fractions

“…26 Other polymers display similar s t r u c t u r e~, 2~-~~ including solution crystallized poly-ethylene3k36 and isotactic polystyrene crystallized from the melt. 37 Welldeveloped hedrites are characterized by extinguished birefringence in that the Maltese cross is lost when viewed normal to the basal plane. This observation suggests that one optical axis is perpendicular to this plane?J1724 This conclusion has been confirmed for polyoxymethylene.26 Some birefringence, as well as a fibrous appearance, can be found in less well-developed hedrites.…”

Influence of molecular composition on the development of microstructure from sheared polyethylene melts: Molecular and lamellar templating

“…To enhance understanding of such complex lamellar textures, blending has often been used to induce morphological simplicity. In this respect, the exploitation of isotactic/atactic blends represents a longstanding strategy [24,25]. In polyethylene, the equivalent involves crystallizing a linear material in the presence of less crystallizable branched polymer [26], where the level of branching limits the thickness of lamellar crystals that is attainable and, therefore, the temperature range within which the polymer can be crystallized.…”