Epoxy Homopolymerization as a Tool to Tune the Thermo-Mechanical Properties and Fracture Toughness of Vitrimers

Abstract

Epoxy/dicarboxylic acid vitrimer was prepared by the solvent-free reaction of diglycidyl ether of bisphenol A (DGEBA) and 1,4-cyclohexane dicarboxylic acid (CHDA) with the addition of monobutyltin oxide (Sn) as a catalyst. By tailoring the catalyst content (≥5 mol %), an effective conversion of functional groups during cure demonstrated the network polymerization mechanisms and a sequence of the side reactions. Indeed, the manufactured vitrimers exhibit creep and full stress relaxation thanks to catalytic transesterifications. By changing the epoxy/diacid ratio, the thermo-mechanical properties and mechanical behavior of the epoxy/acid vitrimers can be tuned while keeping self-healing ability. At high epoxy excess, both glass-transition temperature (T g) and solid–liquid viscoelastic transition temperature (T v) shift to a higher temperature. At vitrimer formulations 1:0.6 and 1:0.5 (epoxy/acyl), a remarkable improvement of fracture toughness (K Ic) is observed, indicating the transition from stiff to relatively ductile materials at 1:0.6. This is attributed to the altered network structures due to etherification and epoxy homopolymerization. The rough fracture surface suggests more energy dissipation during crack propagation in vitrimer with a high excess epoxy. After healing, welded vitrimers still exhibit good fracture toughness with only a slight reduction (<10%) in K Ic. We believe that these vitrimer formulations are promising as matrices in the composite fields.

VOC-free tricomponent reaction platform for epoxy network formation mediated by a recyclable ionic liquid

“…These hydroxyl groups are capable of further reacting (i) with SA via condensation forming ester linkages or (ii) with epoxides promoting epoxy ring opening and formation of ether linkages or (iii) with ester bonds via transesterification. 44,54,55…”

Itaconic acid-based hyperbranched polymer toughened epoxy resins with rapid stress relaxation, superb solvent resistance and closed-loop recyclability

“…The stress relaxation and topology rearrangement of epoxy vitrimers can be induced by transesterification reactions of β-hydroxyl ester linkages when the samples were restrained under constant strain at an elevated temperature. [62][63][64][65] To compare the effect of TBD and IAHBP, temperature-dependent stress relaxation measurements were conducted on DGEBA/IA, DGEBA/IA/TBD and DGEBA/IAHBP (Fig. 2a).…”

“…Water and solvent resistance Solvent resistance is a great challenge for mendable and recyclable epoxy resins. [73][74][75] The swelling ratios of DGEBA/IAHBP were compared with the previously-reported epoxy vitrimers 10,12,20,28,30,31,36,42,43,48,61,62,65,[74][75][76] with detailed results in Fig. 2d.…”

Exploring of the property of epoxy resins based on diselenide and disulfide dynamic linkers

“…All of the samples, as shown in Figure 3 , were able to relax stress and flow at temperatures above 90°C, and the normalized stress-relaxation curves at different temperatures (90°C, 100°C, 110°C, and 120 °C). The relaxation time was defined by the Maxwells model as the time it took for the modulus to relax to 1/e of its initial value, or G (t) /G 0 = 0.37 ( Tangthana-umrung et al, 2021 ; Lin et al, 2022 ; Sun et al, 2022 ). The relaxation times of BED4DSe and BED2DSe were 22 s and 34 s at 120°C, respectively, which were much shorter than the disulfide epoxy resin networks (BED4DS and BED2DS).…”