Crystallization of low molecular weight atactic polystyrene

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Atactic polystyrene (a-PS) typically lacks long-range order.
• Previous studies noted unexplained gel and cluster formation in a-PS.

Purpose of the Study:

• To investigate the crystallization behavior of low molecular weight atactic polystyrene.
• To characterize the morphology and thermal properties of observed crystals.
• To explore the implications of this crystallinity for polymer behavior.

Main Methods:

• Atomic force microscopy (AFM) for surface morphology observation.
• Nuclear Magnetic Resonance (NMR) spectroscopy for tacticity determination.
• Differential Scanning Calorimetry (DSC) or similar thermal analysis for melting behavior.

Main Results:

• Observable surface crystals of a-PS with low molecular weight were identified.
• Crystals exhibit thicknesses of a few nanometers and widths from nanometers to microns.
• Crystal growth occurs below approximately 290 K.
• Melting initiates at 302 K, with complete melting observed up to 343 K.
• NMR confirmed the atactic nature of the polystyrene molecules studied.

Conclusions:

• The observed crystallinity arises from inherent variations in stereoregularity within the atactic polymer chains.
• This natural crystallization phenomenon may be linked to previously observed gelation and cluster formation in a-PS.
• The findings align with theoretical predictions suggesting crystallinity is possible across a broad range of polymerization indices, limited by growth kinetics and volume fraction.