Molar Mass Dependent Polymorph Selection of Polybutene-1 Under Compressed CO₂

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Isotactic polybutene-1 (PB-1) typically crystallizes into metastable form II from the melt.
• Form II transitions to stable form I upon aging, involving volume changes.
• Direct formation of stable form I' is a significant research goal.

Purpose of the Study:

• Investigate the effect of molar mass on PB-1 polymorph selection under compressed carbon dioxide (CO2).
• Determine how CO2 pressure influences the crystallization behavior of different PB-1 molar masses.
• Understand the role of crystal morphology in PB-1 polymorph selection.

Main Methods:

• Crystallization of PB-1 with varying molar masses under compressed CO2.
• Analysis of PB-1 polymorphs (form I and form II) using X-ray diffraction or similar techniques.
• Characterization of crystal morphology and chain arrangement.

Main Results:

• Lower molar mass PB-1 showed a higher fraction of form II compared to higher molar mass PB-1 at equivalent CO2 pressures.
• Higher CO2 pressure was needed to suppress form II formation in lower molar mass PB-1.
• Differences in chain morphology within form II crystals were observed: chain-extended for lower M_w and folded-chain for higher M_w.

Conclusions:

• Molar mass significantly impacts PB-1 polymorph selection under compressed CO2.
• Chain morphology (extended vs. folded) dictates polymorph selection by influencing nucleation energy barriers.
• Compressed CO2 offers a route to control PB-1 crystallization, but molar mass must be considered.