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Nanostructure to microstructure self-assembly of aliphatic polyurethanes: the effect on mechanical properties
Abhinay Mishra1, Vinod K Aswal, Pralay Maiti
1School of Materials Science and Technology, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India.
The Journal of Physical Chemistry. B
|April 6, 2010
Summary
Aliphatic polyurethanes self-assemble from nano to microstructures, influencing mechanical properties. Increasing hard segment content enhances crystallinity and modulus but reduces toughness and degradation temperature.
Area of Science:
- Polymer Science
- Materials Science
- Supramolecular Chemistry
Background:
- Polyurethanes (PUs) are versatile polymers with properties tunable by hard segment content (HSC).
- Understanding the self-assembly of aliphatic PUs is crucial for structure-property relationship elucidation.
- Aromatic PUs exhibit different self-assembly behavior compared to aliphatic counterparts.
Purpose of the Study:
- To investigate the step-by-step self-assembly of aliphatic polyurethanes from nanostructures to microstructures.
- To establish the structure-property relationship of aliphatic PUs based on their self-assembled patterns.
- To compare the self-assembly behavior and properties of aliphatic PUs with aromatic PUs.
Main Methods:
- Synthesis of aliphatic polyurethanes with varying HSC (10-80%).
- Characterization using X-ray diffraction (XRD), small-angle neutron scattering (SANS), atomic force microscopy (AFM), and polarizing optical microscopy (POM).
- Electronic structure calculations to understand the origin of self-assembly.
Main Results:
- Self-assembly was observed from 1.6 nm to 2 microm structures.
- Increasing HSC enhanced crystallinity and Young's modulus (percolation at 50% HSC).
- Toughness improved up to 30% HSC, then decreased; degradation temperature decreased with increasing HSC.
Conclusions:
- Aliphatic PUs form loop structures via self-assembly, facilitating hydrogen bonding and compact crystallites.
- The study establishes a clear link between self-assembly, HSC, and mechanical properties in aliphatic PUs.
- Dynamic shear experiments revealed unique domain structure splintering and reformation in aliphatic PUs.
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