Block CO₂-Polycarbonates: Tunable Chain Extension with Zn(II) Carboxylates

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Low molecular weight polymers often lack the desired mechanical properties for advanced applications.
• Dynamic covalent or coordination chemistry offers routes to assemble small polymer chains into higher-order materials.
• Halatopolymers, formed by metal-carboxylate interactions, represent a class of self-healing and recyclable materials.

Purpose of the Study:

• To synthesize and characterize novel dynamic halatopolymers from triblock polymers.
• To investigate the effect of controlled chain coupling on material properties.
• To establish a modular strategy for creating tunable polymeric materials from renewable resources.

Main Methods:

• Synthesis of α,ω-dicarboxylic acid triblock polymers (polycarbonate-polyester-polycarbonate).
• Assembly into halatopolymers using Zn(II) coordination with varying amounts of 4-tert-butylbenzoic acid (tBBA) capping ligand.
• Rheological measurements (viscosity, relaxation dynamics) and mechanical testing (creep recovery, temperature ramps).

Main Results:

• Increased Zn(II)-carboxylate chain coupling, achieved by reducing tBBA content, led to higher effective halatopolymer molar mass.
• Enhanced chain coupling resulted in increased zero-shear viscosity, slower relaxation dynamics, and more pronounced elastic behavior.
• Polymers exhibited improved dimensional stability and reduced flow under load with increased coupling; purely viscous behavior was observed without Zn(II).

Conclusions:

• Reversible Zn(II)-carboxylate interactions are crucial for forming dynamic polymer networks.
• The presented modular strategy allows for the conversion of low molecular weight polymers into tunable, high-performance materials.
• This approach offers a design platform for next-generation polymeric materials with controllable properties.