Anisotropic Hydrolysis Susceptibility in Deformed Polydimethylsiloxanes

Area of Science:

• Materials Science
• Computational Chemistry
• Polymer Chemistry

Background:

• Polydimethylsiloxane (PDMS) backbone degradation affects silicone mechanical properties.
• Understanding chemical susceptibility drivers is crucial for material longevity.

Purpose of the Study:

• Identify electronic drivers for chemical susceptibility in strained PDMS.
• Explore the interplay of hydrolysis, mechanical deformation, water attack, and chain mobility.

Main Methods:

• Utilized two levels of quantum chemical theory: Density Functional Theory (DFT) and Density Functional Tight Binding (DFTB).
• Calculated reaction pathways and configuration space to assess hydrolysis susceptibility.
• Computed chain scission probabilities based on backbone degrees of freedom.

Main Results:

• Hydrolysis susceptibility strongly depends on the water attack vector on silicon atoms, correlating with strain-induced electronic structure changes.
• Significant hydrolysis requires concerted strain over multiple monomer units.
• Sustained tension across multiple monomers enhances susceptibility, enabling barrierless scission reactions.

Conclusions:

• Local mechanical deformation and environmental moisture synergistically drive hydrolytic degradation in silicones.
• Quantum chemical insights provide a physical basis for silicone material failure mechanisms.
• Computational methods like DFTB offer efficient exploration of complex degradation pathways.