Toughening Ionic Polymer Using Bulky Alkylammonium Counterions and Comb Architecture

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Supramolecular Chemistry

Background:

• Ionic interactions enhance toughness in flexible polymers like hydrogels and elastomers.
• Toughening rigid polymers via ionic interactions often leads to reduced elastic modulus due to plasticization.
• A need exists for methods to toughen rigid polymers without compromising their mechanical integrity.

Purpose of the Study:

• To develop a strategy for toughening rigid polymers without sacrificing elastic modulus.
• To investigate the effect of counterion size on the mechanical properties of ionic comb polymers.
• To explore the potential of ionic interactions for creating robust and tough polymeric materials.

Main Methods:

• Synthesis of ionic comb polymers with oligoethylene glycol side chains on a polynorbornene backbone.
• Neutralization of carboxylic acid groups with trialkylamines of varying chain lengths (ethyl to octyl) to form ammonium counterions.
• Mechanical testing, including tensile tests at various strain rates, to evaluate ultimate strength, toughness, and elastic modulus.

Main Results:

• Counterion size significantly influenced ultimate strength and toughness, but not elongation at break or elastic modulus.
• The ionic comb polymer with heptylammonium counterions exhibited the highest toughness (77 MJ m⁻³).
• Rate-dependent mechanical behavior was observed, particularly between heptylammonium and octylammonium counterions, suggesting sacrificial bond mechanisms.

Conclusions:

• Bulky ammonium counterions in ionic comb polymers can enhance toughness without plasticization.
• Heptylammonium counterions act as effective sacrificial bonds, moderating dissociation rates for improved toughening.
• This strategy offers a pathway to design high-performance, tough rigid polymers for advanced applications.