Structural-mechanical phase diagram of isotactic polypropylene

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Isotactic polypropylene (iPP) exhibits polymorphism, with alpha and gamma phases commonly observed.
• Metallocene catalysts influence the stereoregularity of iPP, affecting its crystalline structure.
• Plastic deformation can induce phase transformations in semi-crystalline polymers.

Purpose of the Study:

• To investigate the polymorphic transformations of isotactic polypropylene during plastic deformation.
• To understand the role of stereoregularity and metallocene catalysts in these transformations.
• To establish a phase diagram for iPP based on stereoregularity and deformation.

Main Methods:

• Preparation of isotactic polypropylene samples with varying stereoregularity using metallocene catalysts.
• Mechanical testing (stretching) to induce plastic deformation.
• Analysis of crystalline phase transformations using techniques such as X-ray diffraction (implied).

Main Results:

• Unstretched iPP samples containing alpha or gamma crystalline forms transform into a mesomorphic phase upon stretching.
• The mesophase formation facilitates further deformation to high strains.
• This transformation leads to enhanced properties of flexibility and elasticity.

Conclusions:

• The mesomorphic phase is crucial for achieving high deformability and unique elastic properties in iPP.
• A phase diagram illustrating the stability regions of different polymorphic forms as a function of stereoregularity and deformation has been developed.