Characterization of the Temperature Dependent Chemical and Mechanical Properties of a Diels-Alder Based Crosslinked Polymeric Material

A cross-linked polymeric material was formed by the Diels-Alder

reaction between trisfuran and bismaleimide monomers. At elevated

temperatures, chemical equilibrium shifts from the Diels-Alder

reaction to the retro-Diels-Alder reaction, resulting in

depolymerization. As a consequence, the material is both

reversibly gelled and vitrified, existing as a liquid, polymer gel, or

polymer glass, depending on the temperature and relative reaction progress. FTIR spectroscopy was used to characterize the

conversion of furan and maleimide functionalities to the

oxy-norbornene adduct. Equilibrium conversion of the furan and

maleimide varied from 74 % at 85 degrees Celsius to 24% at 45 degrees

Celsius, demonstrating significant reversion via the retro-Diels-Alder

reaction. At lower temperatures vitrification and the subsequent mass transfer restrictions limit the extent of reaction rather than equilibrium. As a consequence the

highest conversion realized was 87% at 45 degrees Celsius. The

thermomechanical properties of the material were characterized by

rheometry. Both the storage and loss moduli were found to decrease

with increased temperature due to decreasing crosslink density, a result

of the retro-Diels-Alder reaction. The gel point, as determined by

the Chambon-Winters criterion, occurs at 92 degrees Celsius,

corresponding to a 71% conversion of functional groups and consistent

with the Flory-Stockmeyer equation for a stoichiometric mixture of A3

and B2 monomers.