Gelation Dynamics in Polydimethylsiloxane Bottlebrush Elastomers

Area of Science:

• Polymer Science
• Materials Science
• Rheology

Background:

• Bottlebrush architectures, characterized by grafted side chains, offer unique entanglement-free properties.
• Network formation in elastomers involves complex interactions between cross-linkers and polymer chains.
• Understanding these processes is crucial for designing advanced elastomeric materials.

Purpose of the Study:

• To investigate network formation in elastomers with grafted side chains (bottlebrush architecture).
• To understand the influence of reaction kinetics and steric effects on network percolation.
• To analyze the impact of side chains on the viscoelastic properties and internal structure of polymer networks.

Main Methods:

• Time-resolved rheology was employed to measure evolving viscoelasticity during catalytic curing.
• Catalyst concentration was tuned to study the impact of reaction kinetics on the sol-gel transition.
• Time-cure superposition was applied to quantify dynamics in pre- and post-gel states.

Main Results:

• Network formation in both bottlebrush and linear systems was found to be independent of cure rate.
• Side chains significantly reduced the fractal dimension of the critical gel cluster.
• The divergence and collapse of shift factors around the gel point indicated universality, independent of cure kinetics.

Conclusions:

• The study elucidates the entanglement-free nature of bottlebrush elastomers and their unique network formation pathways.
• Reaction kinetics and steric effects critically influence network percolation and structure.
• The findings are vital for the application of bottlebrush elastomers in various fields.