Cross-Linking of Sago Starch with Furan and Bismaleimide via the Diels-Alder Reaction

Abstract

This research paper describes the synthesis of thermo-reversible cross-linking of sago starch by grafting a furan pendant group (methyl 2-furoate) onto the starch backbone, followed by a Diels-Alder (DA) reaction of the furan functional group with 1,1′-(methylenedi-4,1-phenylene) bismaleimide (BM). The proof of principles was provided by FTIR and 1 H-NMR analyses. The relevant FTIR peaks are the carbonyl peak (υ C=O sym) at 1721 cm −1 ; the two peaks appeared after DA cross-linking, i.e., at 1510 cm −1 (corresponding to υ CH=CH BM aromatic rings, stretching vibrations), and at 1173 cm −1 (assigned to cycloadduct (C-O-C, δ DA ring)) while the 1 H-NMR result shows evidence for the presence of a furan ring in the starch matrices (in the range of δ 6.3-7.5 ppm). The crosslinked starch product is indeed thermally reversible, as is evident from the appearance of exothermal (DA, temperature range of 50°C-70°C) and endothermal (retro DA, temperature range of 125°C-150°C) transitions in the DSC thermograms. This paper not only proves the thermal reversibility but also demonstrates that the final product properties (chemical, morphology, and thermal stability) can be tuned by varying the annealing temperature, BM intake, and reaction time.