Crystallization Kinetics and Polymorphic Transformations in Polybutene-1.

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Kinetics

Background:

• Polybutene-1 (PB-1) exhibits complex crystalline phase behavior upon cooling from its melt.
• Understanding PB-1 crystallization is crucial for its application in various industries.
• Previous studies have identified different crystalline forms, but detailed kinetic and thermodynamic data are needed.

Purpose of the Study:

• To investigate the kinetics of polybutene-1 crystallization from melt to form 2.
• To analyze the subsequent crystal-crystal transformation from form 2 to form 1.
• To determine thermodynamic parameters such as surface free energies and work of chain folding.

Main Methods:

• Optical microscopy and dilatometry were employed to monitor the crystallization process.
• Avrami analysis was used to describe the kinetics of both form 2 formation and the form 2 to form 1 transformation.
• Specific volume measurements were used to establish a crystallinity scale.

Main Results:

• Polybutene-1 transforms to spherulitic crystalline form 2 between 90-110 °C, with nucleation-controlled spherical growth (Avrami n=3).
• Surface free energies (σ=7.2 mJ/m², σ_b=15.5 mJ/m²) and work of chain folding (q=1.7 × 10⁻¹³ erg/fold) were quantified.
• Form 2 slowly converts to the more stable form 1 near room temperature (Avrami n=2), increasing crystallinity from 52% to 77%.

Conclusions:

• Form 1 is the thermodynamically stable crystalline phase of polybutene-1 below its melting point.
• The work of chain folding in PB-1 is comparable to polyethylene and influences equilibrium melting temperatures.
• Estimated equilibrium melting temperatures are ~128 °C for form 2 and ~141 °C for form 1.