Thermodynamic Origin of Multistep Polymer Crystallization

Area of Science:

• Materials Science
• Polymer Physics
• Computational Chemistry

Background:

• Polymer crystallization is a complex process influencing material properties.
• Understanding the intermediate phases (mesophases) is crucial for controlling final crystalline structures.
• The roles of molecular structure, such as backbone stiffness and monomer interactions, are key factors.

Purpose of the Study:

• To predict the free energy of polymer crystallization using atomistic simulations and theories.
• To elucidate the influence of backbone stiffness and inter-monomer coupling on the formation of metastable mesophases.
• To compare the crystallization behavior of polyethylene and isotactic polypropylene.

Main Methods:

• Atomistic simulations were employed to model polymer behavior.
• Theoretical frameworks were integrated with simulations to calculate free energy.
• Phase transition temperatures were predicted and compared with experimental data.

Main Results:

• Polymer backbone stiffness dictates crystallization pathways.
• Polyethylene, with sufficient stiffness, forms uniaxial order via nematic and rotator mesophases before crystallization.
• Isotactic polypropylene, with lower stiffness, crystallizes directly from the isotropic to the crystalline phase.
• Predicted transition temperatures for polyethylene and isotactic polypropylene align well with experimental observations.

Conclusions:

• Backbone stiffness and monomer orientational coupling are critical determinants of polymer crystallization pathways.
• The study successfully models the distinct crystallization behaviors of polyethylene and isotactic polypropylene.
• The findings provide a theoretical basis for understanding and controlling polymer mesophase formation and subsequent crystallization.