Recyclable Epoxy Resin via Simultaneous Dual Permanent/Reversible Crosslinking Based on Diels–Alder Chemistry

Abstract

Taking advantage of the reversible Diels-Alder (DA) reaction, a simple strategy to obtain recyclable epoxy resins is presented. For this purpose, blends of furan-functionalized and nonfunctionalized epoxy resin are prepared. After the addition of diamine and bismaleimide, blends are heated at 150°C for 5 min, where the permanent amine/epoxy reaction has taken place and upon cooling to room temperature the reversible DA reaction has happened, giving rise to a dual permanent/nonpermanent network. Both reactions are confirmed by Fourier-transform infrared (FTIR) and 13 C-crosspolarization, magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR). Modulated differential scanning calorimetry (MDSC)shows that the epoxy/amine and bismaleimide/amine curing reaction take place, after the DA reaction, simultaneously with the retroDA reaction and before the bismaleimide homopolymerization. Therefore, under the appropriate curing conditions, the Michael's addition and the bismaleimide homopolymerization do not avoid the formation of a hybrid network, as stated in other reports. The reversibility of the DA reaction in three consecutive cycles is confirmed by DSC. Finally, the dual-cured sample is reprocessed three times without significant loss of mechanical properties.

Furan Polymers: State of the Art and Perspectives

“…The fundamental issue in all these materials is of course their thermally reversible deconstruction, leading to such prized properties as self-mending and recyclability, which have been applied in such diverse technologies as coatings (including epoxy resin [55] ), reversible crosslinking of renewable materials [56] (including hydrogels), hot melt adhesives, [57] and the biomedical area, [58] among others.…”

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

“…[ 18–21 ] In the field of composite and nanocomposite materials, thermally reversible matrices may enhance filler recovery (reinforced fibers) and of the matrix itself. [ 22–25 ]…”

“…[18][19][20][21] In the field of composite and nanocomposite materials, thermally reversible matrices may enhance filler recovery (reinforced fibers) and of the matrix itself. [22][23][24][25] Self-healing study of crosslinked polymer: a) Optimal microscopy of a sample cut with a razorblade (left) and the sample after one day of healing at 50 °C (right). b) Scanning electron microscope images at the healing site of i) the original scratch, ii) the scratch after one day at 50 °C, and iii) scratch after heating at 100 °C for 1 h followed by one day heating at 50 °C.…”

Mechanical properties and reprocessability ofDiels‐Alder‐based reversible networks from furan‐modified resins

“…8 As an example, this has been achieved by synthesizing DA-epoxy copolymers, in which the crosslinked network is made of both reversible DA and irreversible epoxy-amine bonds. [9][10][11] Alternatively, Zolghadr et al, proposed a semi-interpenetrated polymer network, in which an epoxy network made of DGEBA crosslinked with DDM is blended with a Diels-Alder poly-adduct obtained from a furan-functionalized resin reacted with bismaleimide. 12 Recently, to improve thermal, mechanical, and healing properties of their resin, Shibata and co-workers combined the DA reaction between a furan-functionalized precursor and a bismaleimide crosslinker with the Michael addition reaction between bismaleimide and melamine.…”