Measuring Tie Chains and Trapped Entanglements in Semicrystalline Polymers

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Quantifying elastically effective molecules (stress transmitters) in semicrystalline polymers is crucial for understanding mechanical properties.
• Existing methods may lack precision or require labels, limiting their applicability.

Purpose of the Study:

• Develop and demonstrate a novel label-free method for quantifying elastically effective molecule content (p) in semicrystalline polymers.
• Correlate this content with mechanical properties and compare with theoretical models.

Main Methods:

• Utilized swelling with deuterated vapor and small-angle neutron scattering (SANS) for label-free quantification.
• Compared experimental results with semi-empirical predictions and structural parameters (e.g., strain hardening modulus, beta parameter).

Main Results:

• Established a strong correspondence between initial elastically active molecule networks and post-yield tensile values.
• Simulations indicated homopolymers have more bridging entanglements than copolymers.
• Found modified Flory-Rehner theory fits experimental data, unlike Michaels-Hausslein theory.

Conclusions:

• The initial molecular network dictates post-yield tensile properties, regardless of subsequent morphological changes.
• Tie molecules have a greater impact on mechanical properties than bridging entanglements.
• The developed method provides a reliable way to quantify critical molecular parameters in polymers.