Rheological and Chemical Analysis of Reverse Gelation in a Covalently Cross-Linked Diels−Alder Polymer Network

Abstract

A network polymer, incorporating dynamic and reversible cross-links, was synthesized using the Diels−Alder reaction. Fourier transform infrared (FTIR) spectroscopy was used to characterize the reaction rate and thermodynamic equilibrium over a broad temperature range. Equilibrium conversion of the furan and maleimide varied from 74% at 85 °C to 24% at 155 °C, demonstrating significant depolymerization via the retro-Diels−Alder reaction. The gel point temperature, as determined by rheometry using the Winter−Chambon criterion, was 92 °C, corresponding to a gel-point conversion of 71%, consistent with the Flory−Stockmayer equation. The scaling exponents for the complex moduli, viscosity, and plateau modulus, in the vicinity of the gel-point, were determined and compared with experimental and theoretical literature values. Further, the material exhibited a low frequency relaxation owing to dynamic rearrangement of cross-links by the Diels−Alder and retro-Diels−Alder reactions.