Cross Nucleation in Polyethylene with Precisely Spaced Ethyl Branches.

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Phenomena

Background:

• Cross nucleation involves one crystalline polymorph (A) inducing the nucleation of a different polymorph (B) without transformation.
• While observed in small molecules, evidence for cross nucleation in crystalline polymers has been limited.
• Understanding polymer crystallization is crucial for tailoring material properties.

Purpose of the Study:

• To investigate and confirm the occurrence of cross nucleation in a crystalline polymer system.
• To characterize the crystallographic and kinetic aspects of this phenomenon in polymers.

Main Methods:

• Isothermal crystallization of polyethylene with precisely spaced ethyl branches.
• Polarized optical microscopy to observe spherulite growth and measure radial growth rates.
• Scanning microbeam wide-angle X-ray scattering (WAXS) to determine crystalline polymorphs.

Main Results:

• New spherulites nucleated at the growth front of initially formed spherulites in branched polyethylene.
• The newly grown spherulites exhibited a faster radial growth rate (1.01 μm/min) than the initial ones (0.76 μm/min).
• WAXS confirmed that the initial and newly formed spherulites possessed different crystalline polymorphs.

Conclusions:

• This study provides the first definitive evidence of cross nucleation in a crystalline polymer.
• The observed faster growth rate of the secondary polymorph supports the criteria for cross nucleation.
• This finding opens new avenues for controlling polymer morphology and properties through crystallization engineering.