Maleimide Self-Reaction in Furan/Maleimide-Based Reversibly Crosslinked Polyketones: Processing Limitation or Potential Advantage?

Abstract

Polymers crosslinked via furan/maleimide thermo-reversible chemistry have been extensively explored as reprocessable and self-healing thermosets and elastomers. For such applications, it is important that the thermo-reversible features are reproducible after many reprocessing and healing cycles. Therefore, side reactions are undesirable. However, we have noticed irreversible changes in the mechanical properties of such materials when exposing them to temperatures around 150 °C. In this work, we study whether these changes are due to the self-reaction of maleimide moieties that may take place at this rather low temperature. In order to do so, we prepared a furan-grafted polyketone crosslinked with the commonly used aromatic bismaleimide (1,1′-(methylenedi-4,1-phenylene)bismaleimide), and exposed it to isothermal treatments at 150 °C. The changes in the chemistry and thermo-mechanical properties were mainly studied by infrared spectroscopy, 1H-NMR, and rheology. Our results indicate that maleimide self-reaction does take place in the studied polymer system. This finding comes along with limitations over the reprocessing and self-healing procedures for furan/maleimide-based reversibly crosslinked polymers that present their softening (decrosslinking) point at relatively high temperatures. On the other hand, the side reaction can also be used to tune the properties of such polymer products via in situ thermal treatments.

Chitosan Hydrogels Based on the Diels–Alder Click Reaction: Rheological and Kinetic Study

“…The FTIR spectra of the N -furfuryl chitosan, PEG-bismaleimide, and the Diels–Alder adduct hydrogel are presented in Figure S3 . The bismaleimide compound exhibits the characteristic bands of poly(ethylene glycol)s and maleimide groups, particularly the bands at 1707 cm −1 (C=O stretching), 1466 cm −1 (C=C stretching), 1341 cm −1 (C–N stretching), 1150 cm −1 (C–N–C bending), 840 cm −1 (C–H wagging vibration), and 695 cm −1 (=C–H out-of-plane bending) [ 20 , 21 , 22 ]. The chitosan derivative, among others, displays the signals corresponding to the furan ring: 1374 cm −1 (C=C furan ring stretching vibration), 895 cm −1 (out-of-plane deformation vibration), and 660 cm −1 (furan ring deformation).…”

Designing End‐of‐Life Recyclable Polymers via Diels–Alder Chemistry: A Review on the Kinetics of Reversible Reactions

“…Ultrasound can still be used to ease the reverse DA reaction and to prevent elevated temperatures causing extra irreversible side reactions, such as maleimide homo‐polymerization. [ 42 ]…”

“…They are different when nonstoichiometric amounts are added, or when making allowances for possible side reactions. [42] By combining the equations we obtain Equation (4), a relation for the change of maleimide conversion over time.…”

“…Ultrasound can still be used to ease the reverse DA reaction and to prevent elevated temperatures causing extra irreversible side reactions, such as maleimide homopolymerization. [42] Some researchers took the approach of applying UV irradiation. They demonstrated this using anthracene as diene instead of furan.…”

“…They are different when nonstoichiometric amounts are added, or when making allowances for possible side reactions. [ 42 ] By combining the equations we obtain Equation (), a relation for the change of maleimide conversion over time. $$\begin{eqnarray}{\frac{{{\rm{d}}x}}{{{\rm{d}}t}}} = {{k_{{\rm{da}}}}{[ M ]_0}( {1 - x} )\left( {\frac{1}{r} - x} \right) - {k_{{\rm{rda}}}}x} \end{eqnarray}$$…”