Compressing and Swelling To Study the Structure of Extremely Soft Bottlebrush Networks Prepared by ROMP

Area of Science:

• Polymer Chemistry
• Materials Science
• Network Polymers

Background:

• Bottlebrush polymers are model materials requiring robust synthetic platforms.
• Ring-opening metathesis polymerization (ROMP) is effective for bottlebrush synthesis but not yet for networks.
• Existing polymer networks often have high moduli, limiting applications.

Purpose of the Study:

• To establish a versatile synthetic platform for bottlebrush polymer networks using ROMP.
• To investigate the relationship between synthesis parameters and network properties.
• To demonstrate control over network properties by varying macromonomer to cross-linker ratios.

Main Methods:

• Polymerization of poly(n-butyl acrylate) macromonomer and dinorbornene cross-linker via ROMP using a third-generation Grubbs' catalyst.
• Systematic variation of macromonomer to cross-linker ratios ([MM]/[XL]) from 10 to 100.
• Contact adhesion testing to quantify dry-state shear modulus (G) and swelling ratio (Q) in toluene.

Main Results:

• Achieved bottlebrush networks with gel fractions exceeding 90% across all tested ratios.
• Quantified dry-state shear modulus (G) ranging from 1 to 10 kPa, demonstrating low moduli achievable.
• Established a scaling relationship G ~ ([MM]/[XL])^-0.81, linking ratio to cross-linking density.
• Validated universal scaling G ~ Q^-1.75 with a measured exponent of -1.71, showing good agreement with linear networks.

Conclusions:

• The developed ROMP platform offers a flexible route to diverse bottlebrush polymer networks.
• Control over macromonomer to cross-linker ratio effectively tunes network properties like shear modulus.
• These bottlebrush polymer networks are promising for applications requiring tunable, low-modulus materials.