The Formation of Curved Polymer Crystals: Poly (4-methylpentene-1)

Area of Science:

• Polymer Science
• Crystallography
• Materials Science

Background:

• Poly(4-methylpentene-1) (PMP-1) exhibits a tetragonal unit cell (Modification I).
• Crystal habit is influenced by growth conditions, particularly temperature and solvent systems.

Purpose of the Study:

• To investigate the effect of crystallization temperature on the habits of PMP-1 lamellar crystals.
• To elucidate the morphological changes from planar to curved, bowl-shaped structures.

Main Methods:

• Optical and electron microscopy were employed.
• Crystallization was performed from polymer solutions in xylene/amyl acetate mixtures at controlled temperatures (50-90 °C).

Main Results:

• A clear trend was observed: lower crystallization temperatures resulted in more pronouncedly curved lamellar crystals.
• Crystals ranged from planar, four-sectored lamellae at higher temperatures to distinctly curved, hollow bowl-shaped structures at lower temperatures.
• Curved crystals exhibited multi-sectored lamellae with peripheral microfaceted outgrowths, unlike the planar crystals.

Conclusions:

• Crystallization temperature is a critical factor controlling PMP-1 crystal morphology.
• A working model is proposed to explain the observed trend of increasing curvature with decreasing temperature, involving growth mechanisms and supercooling effects.