Brønsted-Acid-Catalyzed Exchange in Polyester Dynamic Covalent Networks

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Chemistry

Background:

• Dynamic covalent chemistry enables polymer network rearrangement.
• Vitrimers offer tunable properties through reversible crosslinks.
• Catalyst choice significantly impacts dynamic covalent exchange rates.

Purpose of the Study:

• To systematically investigate the effect of Brønsted acid catalyst strength on polyester-alcohol dynamic covalent exchange.
• To correlate kinetic parameters with acid strength (pKa).
• To compare Brønsted acid catalysts with Lewis acid alternatives.

Main Methods:

• Utilized a low-glass transition temperature (Tg) poly(4-methylcaprolactone) vitrimer formulation.
• Employed various Brønsted acids with differing pKa values.
• Measured network relaxation times, activation energies, and Arrhenius prefactors.

Main Results:

• Strong protic acids facilitated network relaxation at 25 °C (10^4-10^5 s).
• Lewis acids required temperatures above 100 °C for similar relaxation.
• Activation energies ranged from 49-67 kJ/mol, increasing with decreasing pKa.
• Arrhenius prefactors showed an inverse trend to activation energy.

Conclusions:

• Brønsted acid strength is a critical factor in controlling the rate of dynamic covalent exchange in vitrimers.
• Quantitative understanding of these effects aids in designing materials for specific applications.
• This work provides a foundation for future acid-catalyzed dynamic covalent bond exchange studies.